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OCR Additional ScienceOCR Additional Science

Radiation for LifeRadiation for Life

Revision PowerPoint!Revision PowerPoint!

VV

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Static ElectricityStatic ElectricityStatic electricity is when charge “builds up” on an object and then stays “static”. How the charge builds up depends on what materials are used:

+ -

+-

+

+-

-

-+

+

+

-

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+

+

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Static ElectricityStatic Electricity

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+ --

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Van de Graaf generatorsVan de Graaf generators

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Use of static - PhotocopiersUse of static - PhotocopiersPhotocopiers use static electricity. They work by: 1) Copying an ______ of the page onto a ______ plate, 2) Light then causes the charge to ____ away, leaving an “electrostatic impression” of the page, 3) The charges left on the plate ______ small drops of black powder, 4) The powder is transferred from the plate onto the _____, 5) The paper is _____ to “fix” the powder.

Words – heated, leak, paper, image, charged, attract

P

++

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1)

+++++2)

3+4) +

++++

21/04/23Uses of Static – Smoke Uses of Static – Smoke PrecipitatorsPrecipitators

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+ ++

Chimney

Negatively charged

plates

Positively charged

grid

21/04/23Uses and dangers of Static Uses and dangers of Static ElectricityElectricity

Find out how static electricity is used in the following:

1) Laser printers

2) Paint sprayer

3) Defibrillators

Find out how static electricity is dangerous in the following situations:

1) Fuel pipes

2) Hospitals

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Wiring a plugWiring a plug

Earth wire

Neutral wire

Insulation

Live wire

Fuse

1.

2.

3.

4.

5.

6. Cable grip

The live wire of a plug alternates between positive and

negative potential relative to the Earth

The neutral wire of a plug stays at a potential close to zero

relative to the Earth

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FusesFuses

Fuses are _______ devices. If there is a fault in an appliance which causes the ____ and neutral (or earth) wire to cross then a ______ current will flow through the _____ and cause it to _____. This will break the _______ and protect the appliance and user from further _____.

Words – large, harm, safety, melt, live, circuit, fuse

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Earth wiresEarth wiresEarth wires are always used if an appliance has a _____ case. If there is a _____ in the appliance, causing the live wire to ______ the case, the current “_______” down the earth wire and the ______ blows.

Words – fuse, fault, metal, surges, touch

21/04/23Circuit breakersCircuit breakers

Residual Current Circuit Breakers (RCCBs) are often used with fuses. They have some advantages over fuses:

1) They are safer – they don’t get hot

2) They react more quickly

3) They can be switched off for repairs

4) They are easy to reset

5) Each RCCB is attached to a certain circuit, so if one switches off you can see which circuit has a fault

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Georg Simon Ohm 1789-1854

ResistanceResistance

Resistance is anything that will RESIST a current. It is

measured in Ohms, a unit named after me.

The resistance of a component can be calculated using Ohm’s Law:

Resistance = Voltage (in V)

(in ) Current (in A)

V

RI

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An example question:An example question:

V

A

1) What is the resistance across this bulb?

2) Assuming all the bulbs are the same what is the total resistance in this circuit?

Voltmeter reads 10V

Ammeter reads 2A

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ResistanceResistance

Resistance is anything that opposes an electric current.Resistance (Ohms, ) = Potential Difference (volts, V)

Current (amps, A)

What is the resistance of the following:

1) A bulb with a voltage of 3V and a current of 1A.

2) A resistor with a voltage of 12V and a current of 3A

3) A diode with a voltage of 240V and a current of 40A

4) A thermistor with a current of 0.5A and a voltage of 10V

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Waves- Some definitions…Waves- Some definitions…

1) Amplitude – this is “how high” the wave is:

2) Wavelength () – this is the distance between two corresponding points on the wave and is measured in metres:

3) Frequency – this is how many waves pass by every second and is measured in Hertz (Hz)

21/04/23Some definitions…Some definitions…Transverse waves are when the displacement is at right angles to the direction of the wave…

Longitudinal waves are when the displacement is parallel to the direction of the wave…

21/04/23UltrasoundUltrasound

Ultrasonic waves are partly _________ at the boundary as they pass from one _______ to another. The time taken for these reflections can be used to measure the _______ of the reflecting surface and this information is used to build up a __________ of the object.

Words – depth, reflected, picture, medium

Ultrasound is the region of sound above 20,000Hz – it can’t be heard by humans. It can be used in pre-natal scanning:How does it work?

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Other uses of ultrasoundOther uses of ultrasound

1) Echo sounding

The ultrasound is reflected from the sea floor.

2) Breaking down kidney stonesUltrasonic waves break kidney stones into much smaller pieces

3) Cleaning (including teeth)

Ultrasound causes dirt to vibrate dirt off without damaging the object

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The structure of the atomThe structure of the atom

ELECTRON – negative,

mass nearly nothing

PROTON – positive,

same mass as neutron

(“1”)

NEUTRON – neutral,

same mass as proton

(“1”)

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The structure of the atomThe structure of the atom

Particle Relative Mass Relative Charge

Proton 1 +1

Neutron 1 0

Electron 0 -1

MASS NUMBER = number of protons + number of neutrons

SYMBOL

PROTON NUMBER = number of protons (obviously)

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Introduction to RadioactivityIntroduction to RadioactivitySome substances are classed as “radioactive” – this means that they are unstable and continuously give out radiation:

Radiation

The nucleus is more stable after emitting some radiation – this is called “radioactice decay” and the activity is measured in “Becquerels (Bq)”.

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Types of radiationTypes of radiation

1) Alpha () – an atom decays into a new atom and emits an alpha particle (2 protons and 2 ______ – the nucleus of a ______ atom)

2) Beta () – an atom decays into a new atom by changing a neutron into a _______ and electron. The fast moving, high energy electron is called a _____ particle.

3) Gamma – after or decay surplus ______ is sometimes emitted. This is called gamma radiation and has a very high ______ with short wavelength. The atom is not changed.

Unstable nucleus

Unstable nucleus

Unstable nucleus

New nucleus

New nucleus

New nucleus

Alpha particle

Beta particle

Gamma radiation

Words – frequency, proton, energy, neutrons, helium, beta

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Changes in Mass and Proton NumberChanges in Mass and Proton Number

Alpha decay:

Am241

95Np

237

93α

4

2+

90

39Sr

90

38Y β

0

-1+

Beta decay:

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Uses of radioactivity 1Uses of radioactivity 1

Sterilising medical instruments

Gamma rays can be used to kill and sterilise germs without the need for heating.

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Uses of radioactivity 2Uses of radioactivity 2

Rollers

Beta emitter

Beta detector

Paper

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Uses of radioactivity 3Uses of radioactivity 3

Smoke detectors

Alarm

+ve electrode -ve

electrode

Alpha emitter

Ionised air particlesIf smoke enters here a current no longer flows

21/04/23Uses of Radioactivity 4 - Treating Uses of Radioactivity 4 - Treating CancerCancer

High energy gamma radiation can be used to kill cancerous cells. However, care must be taken in order to enure that the gamma radiation does not affect normal tissue as well.

Radioactive iodine can be used to treat thyroid cancer. Iodine is needed by the thyroid so it naturally collects there. Radioactive iodine will then give out beta radiation and kill cancerous cells.

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Half lifeHalf life

The decay of radioisotopes can be used to measure the material’s age. The HALF-LIFE of an atom is the time taken for HALF of the radioisotopes in a sample to decay…

At start there are 16 radioisotope

s

After 1 half life half have

decayed (that’s 8)

After 3 half lives another

2 have decayed (14 altogether)

After 2 half lives another

half have decayed (12 altogether)

= radioisotope = new atom formed

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A radioactive decay graphA radioactive decay graph

Time

Count

1 half life

1 half life

1 half life

21/04/23Dating materials using half-livesDating materials using half-livesQuestion: Uranium decays into lead. The half life of uranium is 4,000,000,000 years. A sample of radioactive rock contains 7 times as much lead as it does uranium. Calculate the age of the sample.

8

8

Answer: The sample was originally completely uranium…

…of the sample

was uranium

4

8

2

8

1

8Now only 4/8 of

the uranium remains – the

other 4/8 is lead

Now only 2/8 of uranium

remains – the other 6/8 is

lead

Now only 1/8 of uranium

remains – the other 7/8 is

leadSo it must have taken 3 half lives for the sample to decay until only 1/8 remained (which means that there is 7 times as much lead). Each half life is 4,000,000,000 years so the sample is 12,000,000,000 years old.

1 half life later…

1 half life later…

1 half life later…

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An exam question…An exam question…

Potassium decays into argon. The half life of potassium is 1.3 billion years. A sample of rock from Mars is found to contain three argon atoms for every atom of potassium. How old is the rock?

(3 marks)

The rock must be 2 half lives old – 2.6 billion years

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Background RadiationBackground Radiation

Radon gas

Food

Cosmic rays

Gamma rays

Medical

Nuclear power

13% are man-made

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Uses of radioisotopes - tracersUses of radioisotopes - tracersA tracer is a small amount of radioactive material used to detect things, e.g. a leak in a pipe:

Gamma source

Tracers can also be used to develop better plant fertilisers and in medicine to detect tumours:

The radiation from the radioactive source is picked up above the ground, enabling the leak in the pipe to be detected.

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Nuclear power stationsNuclear power stationsThese work by using nuclear fission reactions using uranium:

Nuclear fuel is used to boil water in a “heat exchanger”

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Nuclear fissionNuclear fission

Uranium or

plutonium nucleus

Unstable

nucleus New nuclei (e.g. barium

and krypton)

More neutron

s

Neutron

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Chain reactionsChain reactions

Each fission reaction releases neutrons that are used in further reactions.