Physics

Moment of a force:

Moment of a force = force x perpendicular distance of the line if action if the force from fulcrum

Law of moments:

When a body is in equilibrium the sum of the clockwise moments about any point equals the sum of the anticlockwise moments about the same point.

Centre of mass:

I. Centre of mass is the point where whole mass of the body assumes to be concentrated.

II. If the vertical line through the centre of mass is outside the base it will be a topples but if it’s passed

through the base it will be stable.

The stability of the body is increased by:

1. Lowering its centre of mass.

2. Increasing the area of the base.

Energy measurement:

Work is set to be done when a force is applied at an object and the object is moved in the direction of the

force.

work=force ×distance moved∈the direction of force

Kinetic energy:

All moving objects have kinetic energy.

K .E=12

×mass× (velocity )2

Potential energy:

The energy due to change in position, shape, or state.

P .E=mass×gravity ×height

Power:

It’s the rate at which it transfers energy from one form to another.

power=work donetime taken

= energy transfertime taken

Efficiency:

efficiency=useful energy transfered by devicetotal energy applied¿

device ¿×100%

Pressure:

pressure= forcear ea

=pa

pressure=depth×density× gravity=pa

pressure∈gas=atmosphericpressure+excess pressure=pascals

Speed

average speed=distance movedtime taken

Velocity

velocity=distance moved∈stated directiontime taken

velocity=displacementtimetaken

Acceleration

acceleration= changeof velocitytime taken for change

Uniform acceleration

v=u+at

s=(u+v )2

t

s=ut+ 12

a t 2

v2=u2+2as

The heat equation

heat recieved∨given out=mass× temperaturechange ×specific heat capacity

Vsecond speed

Ufirst speed

Sdistance

Specific heat capacity:

The specific heat capacity of a substance is the heat required to produce a 1℃ rise in 1 Kg

Specific heat capacity of water

specific heat capacityof water=heat recevied by water (J )mass ( Kg ) ×temp . rise(℃)

Thermal capacity:

It’s the quantity of heat needed to raise the temperature of the whole body by1℃.

Thermal capacity=mass×specific heat capacity

Specific latent heat of fusion:

The specific latent heat of fusion of a substance is the quantity of heat needed to change unit mass from solid to

liquid without temperature change.

Specific latent heat of fusion

Q=m×l f

Specific latent heat of vaporization:

The specific latent heat of vaporization of a substance is the quantity of heat needed to change unit mass from

liquid to vapor without change of temperature.

Specific latent heat of vaporization

Q=m×l v

Heat supplied by a heater:

Q=P× t=ItV

Speed of wave

speed=frequency×wavelength

Circular motion:

F=mv2

r

The Ampere and the Coulomb

The unit of current is the Ampere (A) which is defined using the magnetic effect.

The unit of charge, the Coulomb (C)

The Coulomb is the charge passing any point in a circuit when a steady current of 1 ampere flows for 1 second,

coulombs (Q)=amperes(I )×time(t)

Series and parallel circuit

The current is the same at all points in a series circuit

The current is different in the branches of a parallel circuit

Direct and alternating current

In a Direct current (d.c) the electrons flow in one direction only.

In an Alternating current (a.c) the direction of flow reverses regularly.

Voltages round a circuit

In series: The voltages at the terminals of a battery equal the sum of the voltages across the devices in the external

circuit from one battery terminal to the other.

In parallel: the voltages across devices in parallel in a circuit are equals.

V= EQ

E=I ×t ×V

Resistance

The opposition if a conductor to a current is called its resistance.

The resistance of a wire of a certain material:

V

i) Increases as its length increases

ii) Increases as its cross-section area decreases

iii) Depends on the material

The Ohm

The ohm is the resistance of a conductor in which the current is 1 ampere when a voltage of 1 volt is applied

across it.

Resistors in series:

V 1=IR1,V 2=IR2 ,V 3=IR3. Also, if R is the combined resistance,v=IR and so IR=IR1+ IR2+ IR3

Dividing both sides by I, R=R1+R2+R3

Resistors in parallel

I 1=VR1

, I 2=VR2

, I 3=VR3

.Also, if R is the combined resistance,

V=IR and so VR

= VR1

+ VR2

+ VR3

Dividing both sides by V,1R

= 1R1

+ 1R2

+ 1R3

For simpler case of two resistors in parallel

1R

= 1R1

+ 1R2

=R2

R1 R2+

R1R1R2

1R

=R2+R1

R1R2

Inverting both sides,

R=R1R2

R1+R2= Product of resistnaces

∑ of resistances

Capacitor

It stores electric charge and is useful in many electronic circuits.

Effects of capacitors in d.c and a.c circuits

The capacitor block d.c

The capacitor passes a.c

Electric power

power=work donetime taken

= energy transfertime taken

E=I ×t ×V

P=IV

Electronic system

Any electronic system consists of three parts:

i) An input sensor or transducerii) A processor

iii) An output transducer

A transducer is a device to convert a non-electrical input into an electrical signal or vice versa.

The processor decides on what action to take on the electrical signal receives from the input sensor;

The output transducer converts the electrical energy supplied by the processor into another form.

Light dependent resistor (LDR)

It’s a type if variable resistor where resistance depends in the amount of light falling on it. It is used in circuits to

detect the level of light

Dark high resistance less current

Light low resistance more current

Thermistor

It’s a type of variable resistor where resistance depends on the temperature.

Cold high resistance less current

Hot low resistance more current

Relays

It’s a type of switch that works using an electromagnet.

Diode

It’s a component that allows the electric current to flow in one direction only. It’s also known as Rectifier. It changes

alternative current to direct current.

Magnetization of iron and steel

Magnetic materials like IRON which magnetize easily but readily lose their magnetism (are easily demagnetized)

are said to be SOFT.

But those like STEEL which are harder to magnetize than iron but stay magnetized are HARD.

Simple d.c electric motor

A direct current (DC) motor is a fairly simple electric motor that uses electricity and

a magnetic field to produce torque, which turns the motor.

Parts of the Motor

DC power supply of some sort Armature or rotor

Commutator Brushes

Lenz’s law

An induced current is always in such a direction as to oppose the motion or change causing it

Sensitivity of a thermometer

It is the length of increase of the liquid per degree rise in temperature. More sensitive means more noticeable

expansion.

Linear scale

When the fixed points of the thermometer have been marked, the distance between them is divided into equal

degrees which are the range of the thermometer.

Range of thermometer

The temperature limits of the thermometer. The lower limit and the upper limit.

Linear expansivity

The expansion can be calculated if:

i) The length of the bridge,ii) The range of temperature it will experience, and

iii) The linear expansivity of the material to be used, Are all known

expansion=linear expansi vity ×original length×temperature rise

Weight

The weight of a body is the force of gravity on it.

Mass

Mass is the amount of matter in an object and is measured in Kg.

Hooke’s law:

Within elastic limit, the force is directly proportional to the extension produced.

Plastic

If a force is applied to an abject, the object changes its shape, and it stays the same shape when the force if

removed.

Elastic

If you put a force on an object making the object change shape and it returns to its original shape after removing

the force. We say the object is Elastic.

Conditions of equilibrium:

I. The sum of the forced in one direction equals the sum of the forces in the opposite directionII. The law of moments must apply.

Stable equilibrium

The body is in stable equilibrium when it slightly displaced and then released, it returns to its previous

position.

Unstable equilibrium

A body is in unstable equilibrium if moves farther away from its previous position when slightly displaced and

then released.

Neutral equilibrium

A body is in neutral equilibrium if it stays in its new position when displayed.

The gas laws

Boyle’s law:

The pressure of fixed mass of gas is inversely proportional to its volume if its temperature is kept

constant.

p= kv

P1V 1=P2V 2

Charles’ law:

The volume of a fixed mass of a gas is directly proportional to its absolute temperature if the pressure is

kept constant.

V 1

T 1

=V 2

T2

Pressure law:

The pressure of a fixed mass of a gas is directly proportional to its absolute temperature if the volume is

kept constant.

p1T1

=p2T2

Combining laws:

P1V 1

T 1

=P2V 2

T 2