HANDOUT OF PHYSICS IGCSE2nd Semester

SECONDARY 5 / YEAR 2012-2013TOPIC: Refers to All Chapters

MEASUREMENT

Quantity and UnitQuantity Unit Symbol

Length Metre m Mass Kilogram kg Time Second s Electric Current Ampere AThermodynamics Temperature

Kelvin K

Luminous Intensity Candela cd Amount of Substance

Mole mol

Scalar and VectorScalar has magnitude only, example: mass, time, speed, distance.Vector has magnitude and direction, example: forces, displacement, velocity, acceleration.

Metre RuleFunction: to measure length up to one metrePrecision: 1 mm or 0.1 cm

CalipersFunction: to measure the diameter of cylinders or circular object

Vernier CalliperFunction: to measure internal dan external diameterPrecision: 0.1 mm or 0.01 cmVernier calipers have two scales, the main scale and the vernier scale.How to use the vernier calipers?

Firstly, grip the object gently using the jaws of the calipers. Then, read the main scale directly opposite the zero mark on the vernier scale. Find the vernier mark coincides with marking on the main scale.

Micrometer Screw GaugeFunction: to measure lengths or thickness in the small scalePrecision: 0.01 mm or 0.001 cmMicrometer screw gauge has two scales, the main scale and fractional scale.How to use micrometer screw gauge?

Turn the thimble until the anvil and the spindle gently grip the object. Then turn the ratchet until it starts to click. Read the main scale reading at the edge of the the thimble. The thimble scale has 50 divisions, each of which is 0.01 mm. Take the timble reading opposite the datum line of the main scale.

Parralax Error: misreading because of the position of the eye to the object. The eyes must be perpendicular to the object.

Instrument Error = uncertainty Zero Error if the position of main scale and vernier scale are not coincides.

Positive zero error zero mark on vernier slightly to the rightNegative zero error zero mark on vernier slightly to the left

Measuring Volume displacement methodSteps:

Select measuring cylinder that is somewhat larger than the object. Partially fill it with water, enough to cover the object. Note the volume of the water. Immerse the object in the water in the cylinder. The increase in its volume is equal to the volume of the object.

Measuring TimeTime can be measured by observing events that repeat at angular period.Each complete to-and-fro motion is one oscillation. The period of the simple pendulum is the time taken for one complete oscillation.

T= tn

Where T is period (s), t is time (t), and n is number of oscillation.

Mass the amount of matter it is made of Density a property of material. It tells us how concentrated its mass is.

Density=mass (kg /g)

volume (m3/cm3)The volume depends on the object given. If the object is in regular shape, volume can be calculated by the formula of the volume. If the object is in irregular shape, volume can be calculated by using displacement method.

DESCRIBING MOTION

Distance, time, speed

speed=distancetime

Average Speed

Average speed= total distancetravelledtotal time taken

Distance – Time GraphsIf the graph slope up gently, showing it was travelling at a slow speedIf the graph becomes steeper, it shows that it moves fasterIf the graph is flat (horizontal), it shows that the speed is constant

Acceleration

acceleration= change∈speedtime taken

Speed – Time GraphsThe steeper the slope, the greater the accelerationA negative slope means a deceleration A horizontal graph (slope = 0) means a constant speedSloping upwards speed increasing (accelerating)Horizontal speed constant (steady speed)Sloping downwards speed decreasing (decelerating)Horizontal speed has decreased to zero (stationary)

Finding Distance Moved by Graphdistance=areaunder speed against time graph

Acceleration from Speed Against Time graphacceleration=gradient of speed against time graph

Acceleration of Free FallIn the absence of air resistance, all objects fall under gravity with constant acceleration (g = 10 m/s2).When there is air resistance, an object falling under gravity experiences decreasing acceleration until terminal velocity is reached. This occurs when the air resistance is equal to the weight of the object.

Air ResistanceAir resistance is a frictional force and it has characteristics: always opposes the motion of moving object, increases with the speed of the object, increases with the surface area of the object, increases with the density of air.

Measuring SpeedIn the laboratory, the speed of a moving trolley can be measured using a light gate connected to an electronic timer. A piece of card, called an interrupt card, is mounted on the trolley. The light gate has a beam of (invisible) infrared radiation. As the trolley passes through the gate, the beam is no longer broken and the timer stops. The faster the trolley is moving, the shorter the time for which the beam is broken. Given the length of the card, the trolley’s speed can be calculated

FORCES AND MOTION

A force is a push or pull that one object exerts on another. It produces or tends to produce motion, and stops or tends to stop motion. The unit of forces states in Newton.

Type of forces: contact force, weight, friction, tension, resistance, electric force, magnetic force.

Adding ForcesParallelogram method using an appropriate scale, represent the two forces using arrows. Complete the parallelogram by draw the image of both vector with the same size and same direction. The resultant force is represented by the diagonal of parallelogram.

Tip to tail method draw the arrow that represent the first force (including the direction), draw another force, which the tail of the second force is in the tip of the first vector. The resultant force is start from the tail of first vector to the tip of second vector.

Force, Mass, AccelerationThe greater the mass of an object, the smaller the acceleration it is given by a particular force, mathematically

F=m .a

Mass, Weight, and GravityMass of an object measured in kilograms, weight of an object measured in Newtons.

W=m. g

Falling through the Air (The Case of Parachute)Parachutist make use of air resistance. A free-fall parachutist jumps out of an aircraft and accelerates downwards. The forces on a parachutist is different in any point of his fall. At first, air resistance hasl little effect. However, air resistance increases as he falls a nd eventually this forces balances his weight. Then the parachutist stips accelerating – he falls at a steady rate known as the terminal velocity. Opening the parachute greatly increases the area and hence the air resitance. Now there is a much bigger force upwards. The forces on the parachutist are again unbalanced, and slows down.

TURNING EFFECT OF FORCES

Moment of ForceThe moment of a force is the product of the force and the perpendicular distance from the pivot to the line of action of the force, mathematically

W=F×dThe moment of a force is bigger if the force is biggerThe moment of a force is bigger if it acts further from the pivotThe moment of a force is greatest if it acts at 90o to the object it acts on

EquilibriumThe conditions that must be met if an object is to be in equilibrium:the forces on it must be balanced (total clockwise = total anticlockwise)the turning effects of the forces on it must also be balanced (no resultant turning effect)

Center of Mass always be in the center of the object (for regular object)

Stability the ability of an object to return to its original position after it has been tilten slightly. To increase the stability of an object, we should ensure that: its center of gravity is low as possible, the area of its base is as wide as possible.

FORCES AND MATTERS

Forces can change the size and shape of an object.

SpringsTo investigate how objects deform, it is simplest to start with a spring. Springs are designed to stretch a long way when a small force is applied, so it is easy to measure how their length increases.

Extension of a SpringAs the force stretching the spring increases, it gets longer. It is important to consider the increase in length of the spring. This quantity is known as the extension.

lengthof streched spring=original length+extension

Hooke’s LawExtension depends on the load. At a certain point, it will reach the elastic limit. The extension of a spring is proportional to the load applied to it, provided the limit of proportionally is not exceeded.

F=kxIn this equation, F is the load (force) stretching the spring, k is the stiffness of the spring, and x is the extension of the spring.

PRESSURE

Pressure in SolidsA large force pressing on a small area gives a high pressure.

pressure= forcearea

The unit of pressure is N/m2 or Pascal (Pa)

Pressure in Liquidspressure=density ×gravity×height

Hydraulic SystemF1A1

=F2A2

or F1×d1=F2×d2

Manometer simple instrument for showing the difference in pressure between two gases or liquids.

Barometer can be used to measure athmospheric pressure

ENERGY TRANSFORMATIONS AND ENERGY TRANSFER

Energy Stores, Energy TransfersEnergy Stores kinetic energy, gravitational potential energy, chemical energy, nuclear energy, nuclear energy, strain energy, internal energyEnergy Transfers electrical energy, thermal energy, light energy, sound energy

Ways of Energy Transfer by a force, by heating, by radiation, by electricity

Energy Conversions when energy changes from one form to another.

Conservation of EnergyIn any energy conversion, the total amount of energy before and after the conversion is constant.

Efficiency

Efficiency=usefulenergy outputenergy input

×100%

Potential EnergyPotential energy is the energy stored on hanging object. An object’s gravitational potential energy depends on the object’s weight (the greater its weight, the greater its potential energy), the object’s height (the greater its height, the greater its potential energy.

PE=mgh

Kinetic EnergyKinetic energy is the energy stored on moving object. Kinetic energy of an object depends on the object’s mass (the greater mass, the greater its kinetic energy) and the object’s speed (the greater the speed, the greater its kinetic energy)

KE=12mv2

Work DoneW=F×d

Power

Power=work done∨energy transferredtime taken

THE KINETIC MODEL OF MATTER

States of MatterState Size Shape

Solid Fixed volume Has a fixed shapeLiquid Fixed volume Takes the shape of

its container

Gas Expands to fill its container

Takes the shape of its container

Change of StateSolid – Liquid meltingSolid – Gas sublimationLiquid – Solid freezingLiquid – Gas evaporationGas – Solid desublimation/deposition/crystallizationGas – Liquid condensationEnergy must be supplied to change a solid into liquid. At the same time, its temperature remains constant as it melts. Similarly, when liquid becomes a gas, its temperature remains constant even though energy is being supplied to it.

Arrangement of ParticlesState Arrangement of Particles Movement of Particles

Solid Packed closely together Vibrate in a fixed position. The hotter the solid, the more they vibrate

Liquid Packed slightly less closely together

Moving in a short distance

Gas Widely separated from one another

Moving freely, bouncing off one another and off the walls of the container

Brownian Motion smoke particles vs. air moleculesThe air molecules are much smaller than the smoke and they can cause the smoke moves around. The air molecules can only do this if they are moving around very fast. It may the air molecules colide with the smoke particles and the wall of the container.

Liquids take up the shape of of their container because their particles are free to move about within the bulk of the liquid.

Gases fill their container, because their particles can move freely about.

Solids retain their shape, because the particles are packed tightly together.

Gases diffuse (spread out) from place to place, so that, for example, we can smell parfume across the room. The parfume particles spread about because they are freely mobile.

Dissolved substances diffuse throughout a liquid. Sugar crystals in a drink dissolve and molecules spread throughout the liquid, carried by the mobile particles. In a hotter drink, the particles are moving faster and the sugear diffuses more quickly.

Most solids expand when they melt. The particles are slightly further apart in a liquid than in a solid.

Liquids expand a lot when they boil. The particles of a gas are much farther apart than in a liquid. We can think about this the other way round. Gases contract a lot when they condense. If all of the air in the room you are now in was cooled enough, it would condense to form a thin layer of liquid, two or three millimetres dep, on the floor.

Why does evaporation make things cooler?The particles that are escaping from the water are the fastest-moving ones. They are the particles with the most energy. This means that the particles that remain are those with less energy, and so the water is colder.

Why do the particles that make up a solid or a liquid stick together?It is because of attractive forces or bonds between the particles. Each particle of a solid is strongly bonded to its neightbours. This is because the forces between particles are strongest when the particles are closed together. In a liquid, the particles are slightly further apart and so the forces between them are slightly weaker. In gas, the particles are far apart, so that the particles do not attract each other and can move freely about.

What happens to the attractive forces as a solid is heated?The particles start to vibrate more and more strongly. Eventually, the particles vibrate sufficiently for some of the bonds to be broken, and a liquid is formed. Heat the material more eventually the particles have suffiecient energy for all the attractive forces between particles to be overcome. The material become a gas. in a gas, the particles are so far apart and moving so fast that they do not stick together. If you cool down a gas, the particles move more slowly. As they collide with one another, there is more chance that they will stick together. Keep cooling the gas and eventually all of the particles stick together to form a liquid.

Evaporation vs BoilingEvaporation is different from boiling. A liquid boils at its boiling point – all of the liquid reaches this temperature and it gradually turns into a gas. evaporation happens at a lower temperature, below the boiling point.

Evaporation – Observation and ExplanationObservation Explanation

A liqui evaporates more rapidly when it is hotter

At higher temperature, more of the particles of the liquid are moving fast enough to escape from the surface

A liquid evaporates more quickly when it is spread out, so that it has a greater surface area

With a greater surface are, more of the particles are close to the surface, and so they can escape more easily

A liquid evaporates more quickly when a draught blows across its surface

A draught is moving air. When particles escape from the water, they are blown away so that they cannot fall back in to the water

Boyle’s Lawp1 .V 1=p2 .V 2

THERMAL PROPERTIES OF MATTER

Expansion in solids, liquids, and gasesMost substances expand when they are heated. This is called as thermal expansion.

Which expands most for a given rise in temperature?Solids expand most slowly when they are heatedLiquids expand faster than solidsGases expand fasterExceptions: liquid paraffin expands very rapidly on heating. Petrol (gasoline) also expands rapidly when it is heated. If, on a hot day a motorist fills up with petrol from cool underground tanks, the fuel may expand and overflow as it warms up.

Specific Heat Capacity – Change the TemperatureSpecific heat capacity of a substance is the energy required to rais the temperature of 1 kg of the substance by 1oC.

Q=mc∆T

Latent Heat – Change the StateEnergy must be supplied to a substance to melt it or to boil it (to change the state). This energy does not increase the substance’s temperature, and for this reason it is known as latent heat. The energy needed to change a liquid into gas is called the latent heat of vaporisation. The energy needed to change a solid into a liquid is called the latent heat of fusion.

The specific latent heat of vaporation is the energy required to cause 1 kg of a substance to change state from liquid to gas at its boiling point. The specific latent heat of fusion is the energy required to cause 1 kg of a substance to change state from solid to liquid at its melting point.

Q=mL

THERMAL ENERGY TRANSFERS

Metals are better conductors of heat than non-metals

ConductionEnergy conducts through solid when neighboring particles collide and share energy, or when electrons transfer energy through the material

ConvectionConvection currents hapen when a fluid expands and rises, because of its lower density. Convectioin current is a movement of a fluid that carried energy from a warmer place to a cooler one.

RadiationInfrared radiation is part of the electromagnetic spectrum

Conduction vs ConvectionIn conduction, energy is transferred through a material from a warmer place to a cooler place without the material itself moving. In convection, energy is transferrred through a material from a warmer place to a cooler place by the movement of the material itself.

Good Absorbers, Good Emitters

Shiny or white surfaces are the best reflectors (the worst absorbers). Matt black surfaces are the best absorbers (the worst reflectors). Matt black surfaces are the best emitters.

SOUND

Sounds are vibrations that travel through a material, produced by a vibrating source

An echo is produced when a sound is reflected off a hard surface

Sound travels through solids (fastest), liquids, and gases (slowest).

The frequency of a sound the number of vibrations per second, measured in Hz.

f= nT

The greater the amplitude of a sound, the louder it is.

The vibrations of a sound travel through a material in the form of compressions and rarefactions of the particles that make up the material

LIGHT

The image formed in a plane mirror: same size, same distance, left-right reversed (laterally inverted), upright, and virtual

RefractionRefraction occurs when a ray of light travels from one material into another. Light travels fastest in a vacuum and almost as fast in air. It travels more slowly in glass, water and other transparent substances.

n= sin isin r

= cv

Total Internal Reflection (the ray is reflected and refracted) - Obey the law of reflectionIf the angle of incidence is greater then a particular value, known as the critical angle, the light is entirely reflected inside the glass. This phenomenon is known as total internal reflection. For total internal reflection to happen, the angle of incidence of the ray must be greater than the critical angle. The critical angle depends on the material being used.

Ray DiagramTo construct ray diagram, draw two rays starting from the top of the object:Ray 1 undeflected through the centre of the lensRay 2 parallel to the axis and then deflected through the principal focus

Magnifying GlassesThe object viewed by a magnifying glass is closer to the lens that the principal focus.Ray 1 undeflected, as it passes through the centre of the lensRay 2 starts off parallel to the axis and is deflected by the lens so that it passes through the principal focus.

The image resulted by magnifying glass: upright, magnified, further from the lens than the object, virtual

PROPERTIES OF WAVES

Wavelength and AmplitudeWavelength of a wave is the distance from one crest of the wave to the next (or from one trough to the next). Since the wavelength is a distance, it is measured in metres, m. Its symbol is λ.

The amplitude of a wave is the maximum distance that the surface of the water is displaced from its undisturbed level – in other workds, the height of a crest. For ripples on the surface of water, the amplitude is a distance, measured in metres, m. It’s symbol is A.

Frequency and PeriodThe frequency of a wave is the number of waves sent out each second. Frequency is measured in herts, Hz. One hertz (1 Hz) is one complete wave or ripple per second.The period of a wave is the time taken for one complete wave to pass a point. The period is measured in seconds, s.

f= 1T

atau T=1f

Transverse and Longitudinal WavesTransverse waves, in which the particles carrying the wave move from side to side, at right angles to the direction in which the wave is moving. Example: ripples on water, light and all other electromagnetic waves.

Longitudinal waves, in which the particles carrying the wave move back and forth, along the direction in which the wave is moving. Example: sound.

Speed, Frequency, and Wavelengthv=λf

Changing Material, Changing SpeedWaves change their wavelength when their speed changes. Their frequency remains constant. Here, light waves slow down when they enter glass and speed up when they return to the air.

Reflection and Refraction of WavesThe law of reflection of light describes how a ray of light behaves when it strikes a flat surface. However, it does not explain how light is reflected. We need the wave theory of light to provide an explanation. Waves are reflected when they strike a surface. If we picture light as a form of wave, then we can predict that it will be reflected in the same way that ripples on the surface of the water are reflected.

Ripples are refracted when their speed changes. We know thet the speed of light changes as light passes from one material to another. So the wave theory of light allows us to predict that light will be refracted.

Diffraction of WavesWaves change their wavelength when their speed changes. Their frequency remains constant. Here, light waves slow down when they enter glass and speed up when they return to the air.

As the ripples arrive the gap in the barrier, the water at the edge of the gap moves up and down. This sets off new circular ripples, which spread out behind the barrier. If you look a the diffracted ripples, you will see that the central part of the ripple remains straight after it has passed through the gap. At the edges, the ripples have the shape of an arc of a circle.

ELECTROMAGNETIC WAVES

The diagram below shows the range of wavelengths and frequencies of the components of the electromagnetic spectrum, and the comparison with common items to give an idea of the sizes.

The uses of the different electromagnetic radiation are shown in the table below:Electromagnetic

radiationDescription Uses

Radio waves Lowest frequencies and longest wavelengths

Used for transmission of signals and data. An antenna is used to receive these signals

Radio broadcasting Transmitting television

programmes Telecommunication Wireles networking

Microwaves Easy to control and direct In a microwave oven, absorbed

microwaves cause water molecules in the food to vibrate rapidly, which then heats up the food

Satellite communication

For cooking food Remote sensing (radar)

Infrared Produced by hot objects Some animals can see in infrared red

light to enable them to detect warm-blooded animals

Night vision binoculars Thermal imaging Remote controls Motion detectors

Visible light Produced by luminous objects (e.g. burning items and stars such as the Sun)

Crucial for normal human sight Used in data transfer in

telecommunications and by electronic devices such as television sets and computer monitor

Optical fibres for data transmission

Endoscopy (visual inspection of internal organs)

Photography

Ultraviolet rays The human skin produces vitamin D naturally when exposed to ultraviolet rays.

Also causes tanning by stimulating

Sunbeds In “black lights” for

medicine , forensics, lighting effects, poly

the production of the skin pigment known as melanin. Can cause sunburn.

Some chemicals absorb ultraviolet radiation and then appear to be gwowing. This fluorescence effect is used to create markings on bank notes, paints and dyes.

merisaion and insect attraction

Fluorescence effect

X – rays High frequencies Able to penetrate many materials Used in the medical field to obtrain

images of the internal parts of our bodies

In scanners in airports to check the contents of luggage bags

Detecting cracks in pipes and buildings

Radiography (diagnostic X-ray images in medicine)

Gamma rays Waves with the highest frequency and most energy

Dangerous rays coming from nuclear explosions and atomic bombs, they can cause cell and tissue injury

As they can cause damage to living cells, they are used in the medical field to kill cancer cells

Sterilisation of medical equipment

Radiotherapy

Dispersion of Light

What happens in a prism to produce a spectrum?As the white light enters the prism, it slows down. We say that it is refracted and, as we have seen, its direction changes. Dispersion occurs because each colour is refracted by a different amount. Violet light slows down the most, and so it is refracted the most. Red light is least affected.

Laser light is not dispersed by a prism. It is refracted so that it changes direction, but it is not split up into a spectrum. This is because it is light of single colour, and is described as monochromatic (one colour)

All types of electromagnetic wave have one thing in common: they travel at the same speed in a vacuum.

MAGNETISM

Magnetic PolesNorth – South attractNort – North or South – South repel

Magnetisation Methodsa. Stroking a piece of the material be stroked with a permanent magnet. By stroking

it consistently from one end to the other (never going in the reverse direction), it becomes magnetised.

b. Electrical Place the material in a strong magnetic field, as produced by an electromagnet. It becomes magnetized.

c. Heating place a long thin piece of the material so that it lies north-south in the Earth’s magnetic field. Heat it. When it cools, it will have been magnetised by the Earth’s field.

d. Hammering alternatively, hammer a piece of the material placed in a north-south direction and it will pick up the Earth’s field. When steel ships are made, they are hammered as the metal plates are riveted together. The whole ship ends up magnetised, so that any compass on board will point the wrong way. The ship has to be demagnetised before it can set sail.

Demagnetisation Methoda. Hammering When a magnet is placed in an east-west direction and hammered, it

loses its magnetism. This explains why the magnets used in school labs gradually lose their magnetism if they are repeatedly dropped and bashed about.

b. Heating if its temperature goes above a certain temperature, it will lose it magnetism.

c. Place the magnet in the field of an elactromagnet that is connected to an alternating current supply. The magnetic field will vary back and forth. Gradually reduce the current to zero. The magnet will be demagnetised.

Magnetic InductionMagnetic induction is the process where ferromagnetic materials such as iron become magnetised when they are near or in contact with a permanent magnet.

Magnetic FieldsDirection come out of north poles and go into south polesStrength lines close together indicate a strong field

Electromagnets - Solenoid

When a current flows through the wire, a magnetic field is produced. The field is similar in the shape to that of a bar magnet. Note that the field lines go all the way through the centre of the coil. There are three ways to increase the strength of and electromagnet:

a. Increase the current flowing through it – the greater the current, the greater the strength of the field

b. Increase the number of turns of wire one the coil – this does not mean making the coil longer, but packing more turns into the same space to concentrate the field

c. Add soft iron coreElectromagnets have great advantage that they can be switched on and off. Simply switch off the current and the field around the coil disappears. This is the basis of a number of applications – for example, the electromagnetic cranes that move large pieces of metal and piles of scrap around in a scrapyard. Electromagnet are also used in electric doorbells, loudspeakers, electric motors, relays and transformers.

The Field Around a SolenoidWhen an electric current flows through a solenoid, a magnetic field is produced inside and outside the coil. This field is similar to that around a bar magnet:a. One end of the solenoid is the north pole and the other end is the south pole. Field

lines emerge from the north pole and go into the south pole.b. The field lines are closest together at the poles, showing that this is where the

magnetic field is strongest.c. The lines spread out from the poles, showing that the field is waker in these regions.The strength of the field can be increased by increaseing the current. The field can be reversed by reversing the diretion of the current.

STATIC ELECTRICITY

When one object is rubbed against another, they may gain opposite electrostatic charges.

Charged objects exert forces on each other: like charges repel; unlike charges attract

An electric field exists anywhere where a charged object experinces a force.

Objects gain an electrostatic charge when they gain or lose electrons.

Electrons have a negative charge, so an object that gains electrons becomes negatively charged. The object that loses electrons becomes positively charged.

A charged object may attract an uncharged object. Electrons in the uncharged object move slightly, so that the object becomes charged by induction.

ELECTRICAL QUANTITIES

Conductors and InsulatorsGood conductors: most metals e.g., copper, silver, gold, steel

Good insulators: polymers, minerals, glass

Electric CurrentA current is a flow of electric charge. Current flows from the positive terminal of the supply, around the circuit, and back to the negative terminal. Electric current flows from positive to negative (conventional current). Electron moves from negative to positive.

I=Qt

AmmeterTo measure electric current, we use an ammeter. There are two types of ammeter, analogue meter and digital meter. An ammeter must be connected into a circuit in series. If the meter is connected the wrong way round, it will give negative readings.

Potential Difference vs Electromotive ForceThe electromotive force of an electrical energy source is defined as the work done by the source in driving a unit charge round a complete circuit. (measuring voltage in the whole circuit)

ϵ=WQ

Potential difference between two points in an elactric circuit is defined as the amount of electrical energy converted to other forms of energy when one coulom of positive charge passes between two points. (measuring voltage between two points)

V=WQ

VoltmeterA voltmeter is always connected across the relevant component, because it measuring the potential difference betwen two ends of the component. Voltmeter are connected across a component, to measure the p.d. across the component.

ResistanceResistance is a measure of how difficult it is for an electric current to pass through a material. How much current can a cell push through a resistor? This depends on the resistance of the resistor. The greater its resistance, the smaller current that will flow through it, the resistance of componen is measured in Ω.

R=VI

Changing CurrentThe greater the resistance in the circuit, the smaller the current that flows. The greater the p.d. in a circuit, the greater the current that flows.

ResistivityThe resistance of a metallic conductor is a constant if the temperature and other physical conditions remain the same. In general, for metallic wires, the higher the temperature, the larger the resistance. Wires carrying a large current may be heated by the current after some time, hence affecting the overall resistance of a circuit. To ensure we get accurate readings when conducting experiments, it is good practice to use low current.

Besides temperature, the resistance of a conductor also depends on its length, its cross-sectional area or thickness of the wire, and the type of the material, the details as follows:

a. The longer a wire, the greater is its resistanceb. The greater the diameter of a wire, the less is its resistancec. The resistance of awire is proportional to its lengthd. The resistance of a wire inversely proportional to its cross-sectional area.

ρ=RAl

Electrical Power

P= Et=Wt

∨P=IV

ELECTRIC CIRCUITS

Electric Symbols

ResistorsA resistor can be used to control the amount of current flowing around a circuit. A variable resistor (rheostat/potentiometer) can be used to alter the current flowing in a circuit.

TransducersWe use many different electric circuits to make things happen automatically. For example, if the temperature falls, we may want a heater to come on automatically. If someone is moving around inside a bank at night, the burglar alarm must sound. Electronic systems like these depend on devices described as transducers.

Light-dependent resistor (LDR)LDR is a type of variable resistor whose resistance depends on the amount of light falling on it. An LDR is made of a material that does not normally conduct well. In the dark, an LDR has a high resistance, but it has lower resistance in brighter light. LDRs are used in circuits to detect the level of light, for example in security lights that switch on automatically at night.

ThermistorA thermistor is another type of resistor whose resistance depends on its environment. In this case, its resistance depends on its temperature. The resistance changes by large amount over a narrow range of temperature.

CapacitorsA capacitor is a component used in circuits to store energy. You can think of it as being similar to a rechargeable battery. Connect it to a power supply and it will gradually charge up, storing energy until the p.d. across it is equal to the e.m.f. of the supply.

RelaysA relay is a type of switch that works using an electromagnet. A relay is used to link two circuits together. The relay is composed of a coil and a switch.

DiodeA diode is a component that allows electric current to flow in one direction only. Diodes are useful for converting alternating current (A.C.) into direct current (D.C.). This process is known as rectification and the diode acts as a rectifier.

Current, Voltage, and Resistance in Series and ParallelType of circuit Resistors in series Resistors in parallel

Total current I T=I 1=I 2=…=I n I T=I 1+ I 2+…+ I nTotal p.d. V T=V 1+V 2+…+V n V T=V 1=V 2=…=V n

Total resistance RT=R1+R2+…+Rn 1RT

= 1R1

+ 1R2

+…+ 1Rn

Potential Divider

Often, a power supply or a battery provides a fixed potential difference. To obtain a smaller p.d., or a variabble p.d., this fixed p.d. must be split p using a circuit called a potential divider.

V out=( R2R1+R2 )×V

TransistorsA transistor is an electronic component with three terminals or connections. The three terminals are called athe collector (c), base (b), and emitter (e). In the circuits in which we are interested, a transistor acts as a device for controlling the flow of the currents.

base+collertor current=emitter current

Logic GatesA logic gate is device that receives one or more electrical input signals, and produces an output signal that depends on those input signals. These signals are voltages: a high voltage is referred to as ON, and is represented by the symbol 1; a low voltage is reffered to as OFF, and is represented by the symbol 0.

It is easiest to understand this by looking at three specific examples: the AND, OR, and NOT gates, whose circuit symbols are shown as follow:

a. An AND gate functions like this: its output is ON if both input 1 and input 2 are ON, look at this following truth table:

Input 1 Input 2 Output0 0 01 0 00 1 01 1 1

b. An OR gate functions like this: its output is ON if either input 1 or input 2 or both is ON, look at this following truth table:

Input 1 Input 2 Output0 0 01 0 10 1 11 1 1

c. A NOT gate functions like this: its output is ON if its input is not ON, look at this following truth table:

Input 1 Input 20 11 0

d. A NAND gate functions like this: its output is ON if both input 1 and input 2 are not ON, look at this following truth table:

Input 1 Input 2 Output0 0 1

1 0 10 1 11 1 0

e. A NOR gate functions like this: its output is ON if neither input 1 not input 2 is ON, look at this following truth table:

Input 1 Input 2 Output0 0 11 0 00 1 01 1 0

ELECTRICAL SAFETY

Electrical CableThe wires in each cable are insulated from one another, and the whole cable has more protective insulation around the outside. If this insulation is damaged, there is a chance that the user will touch the bare wire and get an electric shock. There is also chance that current will flow between two bare wires, or form one bare wire and any piece of metal it comes into contact with. Often, the metal case of an electrical appliance is earthed by connecting it to the earth wire to reduce the chances of a fatal electric shock. Another hazard can arise if an excessive current flows in the wires. They will heat up and the insulation may melt, causeing it to emit poisonous fumes or even catch fire. Thus it is vital to avoid using appliances that draw too much current from to supply. When using electricity, it is important to avoid damp or wet condition.

Fuses Fuses are included in circuits to stop excessive currents from flowing. If the current gets too high cables can burn out and fires can start. A fuse contains a thin section of wire, designed to meld and break if the current gets above a certain value. Usually, fuses are contained in catridges , which make it easy to replace them, but some fuses use fuse wire. The ticker the wire, the higher the current that is needed to make it ‘blow’. A fuse represents a weak link in the electricity supply chain. Replaceing a fuse is preferable to having to rewire a whole house. It is important to choose a fuse of the correct value in order to protect an appliance. The current rating of the fuse should be just above the value of the current that flows when the appliance is operating normally.

Circuit BrakersThere are two types of circuit breaker used in electrical safety. Both work using electromagnets. The first one is trip switch. It can replace a fuse. When the current flowing through the trip switch exceeds a certain value, the switch ‘trips’, breaking the circuit. If too much current starts to flow, the supply itself might overheat and be damaged. The second one is residual-current device (RCD). It protects the user rather than an appliance or cable.

ELECTROMAGNETIC FORCES

Corkscrew Rule

The rule that the direction of the current and that of the resulting magnetic field are related to each other as the forward travel of a corkscrew and the direction in which it is rotated.

Electric Bells

When the switch is on, the circuit is completed and current flows. The electromagnet becomes magnetised and hence attracts the soft-iron armature and at the same time pull the hammer to strike the gong. This enables the hammer to strike the gong. As soon as the hammer moves towards the gong, the circuit is broken. The current stops flowing and the electromagnet loses its magnetism. This causes the spring to pull back the armature and reconnect the circuit again. When the circuit is connected, the electromagnet regain its magnetism and pull the armature and hence the hammer to strike the gong again. This cycle repeats and the bell rings continuously.

Relays

A relay is an electrical switch that opens and closes under the control of another electric circuit. The switch is operated by an electromagnet to open or close one or many sets of contacts. A relay has at least two circuit. One circuit can be used to control another

circuit. The first circuit (input circuit) supplies current to the electromagnet. The electromagnet is magnetised and attracts one end of the iron armature. The armature is then closes the contacts (second switc) and allows current flows in the second circuit. When the first circuit is open again, the current ot the electromagnet is cut, the electromagnet loses its magnetism and the second switch is opened. Thus current stip to flow in the second circuit.

D.C. Generator

A simple D.C. generator essentially the converse of a D.C. motor with its battery removed. Initially the armature is vertical. No cutting of magnetic flux occurs and hence induced current does not exist. When the armature rotates, the change in flux increases and the induced current correspondingly increases in magnitude. After rotating by 90o, the armature is in the horizontal position. The change in magnetic flux is maximum and hence the maximum induced e.m.f. is produced. Maximum induced current flows though the galvanometer. When the armature continues to rotate, the change in flux decreases. At the 180o position, there is no change in flux hence no iduced current exists. The induced current is achieves its maximum value again when the armature is at 270o. After rotating 360o, the armature returns to its original position. The direction of the induced current can be determined from Fleming’s Right-Hand Rule. Even though the magnitude of the induced current or d.g.e. is dependent on the orientation of the coil, the current in the external circuit always flows in one direction. This uni-directional current is known as direct current.

Fleming’s Left-Hand RuleFleming's right hand rule (for generators) tells us that if we take our right hand and extend the thumb, and also the index and the middle finger such that they are all at right angles to each other, we can discover the direction of the current induced in the wire of the generator. We'll have to know the direction of the motion of the conductor, and the direction of the magnetic field to do this. There are three things with direction.

Cathode Rays OscilloscopeCathode rays are electrons which are emitted from gases trapped inside a cathode ray tube. A cathode ray tube is a glass tube from which most of the air has been evacuated.

The tube has electrodes placed at each end and a high-voltage current is passed through the electrodes. A ray is produced at the cathode (negative pole) and travels to the anode (positive pole). The ray is called "cathode ray" because it comes from the cathode. JJ Thomson used cathode ray tubes to demonstrate that the cathode ray responds to both magnetic and electric fields. Since the ray was attracted to a positive electric plate placed over the cathode ray tube (beam deflected toward the positive plate) he determined that the ray must be composed of negatively charged particles. He called these negative particles "electrons."

The cathode ray oscilloscope is an extremely useful and versatile laboratory instrument used for studying wave shapes of alternating currents and voltages as well as for measurement of voltage, current, power and frequency, in fact, almost any quantity that involves amplitude and waveform. It allows the user to see the amplitude of electrical signals as a function of time on the screen. It is widely used for trouble shooting radio and TV receivers as well as laboratory work involving research and” design. It can also be employed for studying the wave shape of a signal with respect to amplitude distortion and deviation from the normal. In true sense the cathode ray oscilloscope has been one of the most important tools in the design and development of modern electronic circuits.

ELECTROMAGNETIC INDUCTION

Electromagnetic InductionThe process of generating electricity from motion is called electromagnetic induction. A coil of wire and magnet moving relatively to each other are needed to induce voltage accross the ends of a wire. In fact, you dont need to use a coil, a single wire is enough to induce an e.m.f. The wire is connected to a sensitive meter t slow when a current is flowinga. Move one pole of the magnet downwards past the wire, and a current flows.b. Move the magnet back upwards, and a current flows in the opposite direction.c. Reverse the magnet to use the opposite pole, and the current flows in the opposite

directiond. Hold the magnet stationary next to the wire or coil, and no current flows. They must

move reltive to each other, or nothing will happen.

A.C. Generator

Generator can be modified to an A.C. generator by replacing its commutators with two (separate) slip ring. The two slip rings rotate in tandem with the armature. Carbon brushes connect the armature to the external circuit. The armature is initially at the vertical position. No magnetic flux is cut and hence no induced current exists. When the armature rotates, the change in magnetic flux increases and the induced current increases untuil its maximum value at the horizontal position. The direction of the induced current can be determined from Fleming’s Right Hand rule. As the armature rotates, the change in magnetic flux increases and the induced current increases until its maximum value at the horizontal position. The direction of the induced current can be determined from Fleming’s Right Hand rule. As the armature continues on its rotation, the change in magnetic flux decreases until at the vertical position, no induced current exists. Subsequently upon reaching the horizontal position again, the induced current is maximum, but the direction of the induced current flowing through the external circuit is reversed. The direction of the induced current (which flows through the external circuit) keeps changing depending on the orientation of the armature. This induced current is also known as alternating current. The current is positive (+) in one direction and negative in the other (-). The smooth rings play a critical role in the generation of alternating current.

Induction and Field LinesThe factors that affect the magitude and direction of the induced e.m.f.a. If the magnet is tationary, there is no cutting of field lines and so no e.m.f. is

induced.b. If the magnet is further from the wire, the field lines are further apart and so fewer

are cut, giving a smaller e.m.f.c. If the magnet is moved quickly, the lines are cut move quickly and a bigger e.m.f. is

induced.d. A coil gives a bigger effect than a single wire, becaus each turn of wire cuts the

magnetic field lines and each therefore contributes to the induced e.m.f.There are four ways of increasing the voltage generated by an a.c. generator:a. Turn the coil more rapidlyb. Use a coil with more turns of wirec. Use a coul with a bigger aread. Use stronger magnets

THE NUCLEAR ATOM

Alpha particles are positively charged. If they are repelled back from the gold foil, it must be by another positive charge. If only a few were repelled, it was because the positive charge of the gold atoms was concentrated in a tiny space within each atom. Most alpha particles passed straight through because they never went near this concentration of charge. This speck of concentrated positive charge, at the heart of every atom, is what we now call the atom’s nucleus.

Atoms and ElementsThe nucleus of an atom of element X is written as XZ

A

Elements and IsotopesZ+N=A

The isotopes of an element have the same number of protons but different numbers of neutrons in their nuclei.

Isotopes at Work for most chemical elements, at least one isotope is stable; however, other isotopes may be unstable. By this we mean that they undergo radioactive decay, emitting radiation as they change from one element to another.

RADIOACTIVITY

Types of RadiationName Symbol Made of Mass Charge Speed/m/sAlpha α or He2

4 2 protons + 2 neutrons

Approx. (mass of

proton) x 4

+2 ~3 x 107

Beta β or e−10 an electron Approx.

(mass of proton)/184

0

-1 ~2.9 x 108

Gamma γ photon of electromagntic

0 0 3 x 108

Deflecting RadiationAlpha and beta particles are charged, so, when they move, they constitute an electric current. Becausse their opposite signs, the forces on them in a magnetic field are in opposite directions. The direction which the particles are deflected can be predicted using Fleming’s left-hand rule. as in an electric field, gamma rays are not deflected because they are uncharged.

Energy ReleasedRadioactive substances release energy when they decay. Before they decay, this energy is stored in the nucleus of the atom. When it is released, it is in two forms:a. An alpha or beta particle is fast-moving. The nucleus that has emitted it recoils. Both

particles have kinetic energy.b. A gamma ray transfers energy as electromagnetic radiation

Penetrating PowerRadiation can pass through solid materials. Different types of radiation can penetrate different thicknesses of the materials.

a. Alpha particle are the most easily absorbed. They can travel about 5 cm in air before they are absorbed. They are absorbed by athin sheet of paper.

b. Beta particles can travel fairly easily through air or paper. But they are absorbed by a few millimetres of metal.

c. Gamma radiation is the most penetrating. It takes several centmetres of a dense metal like lead, or several metres of concrete, to absorb most of the gamma radiation.

Ionisation and Absorptiona. Alpha particles are the most strongly ionising, so it is the most easily absorbed and

the least penetratingb. Gamma radiation is the least strongly ionising, so it is the least easily absorbed and

the most penetrating

Radioactive Decay (Half-Life)The half-life of a radioactive substance is the average time taken for a half of the atoms in a sample to decay.