OCR Additional Science

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OCR Additional Science
Radiation for Life
W Richards The Weald School
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Static Electricity
Static 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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Static Electricity
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Van de Graaf generators
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Use of static - Photocopiers
Photocopiers 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
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Uses of Static Smoke Precipitators
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Positively charged grid



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Uses and dangers of Static Electricity
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 plug
Earth wire
Live wire
Fuse
Neutral wire
Cable grip
Insulation
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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Fuses
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 wires
Earth 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
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Circuit breakers
Residual Current Circuit Breakers (RCCBs) are
often used with fuses. They have some advantages
over fuses

1. They are safer they dont 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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Resistance
The resistance of a component can be calculated
using Ohms Law
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An example question

1. What is the resistance across this bulb?
2. Assuming all the bulbs are the same what is the
   total resistance in this circuit?

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More examples
6V
12V
What is the resistance of these bulbs?
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Resistance
Resistance is anything that opposes an electric
current.

• What is the resistance of the following
• A bulb with a voltage of 3V and a current of 1A.
• A resistor with a voltage of 12V and a current of
  3A
• A diode with a voltage of 240V and a current of
  40A
• A thermistor with a current of 0.5A and a voltage
  of 10V

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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)
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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
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Ultrasound
Ultrasound is the region of sound above 20,000Hz
it cant be heard by humans. It can be used in
pre-natal scanning
How does it work?
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
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Other uses of ultrasound
1) Echo sounding
The ultrasound is reflected from the sea floor.
2) Breaking down kidney stones
Ultrasonic 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 atom
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The structure of the atom
Particle Relative Mass Relative Charge
Proton 1 1
Neutron 1 0
Electron 0 -1
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Introduction to Radioactivity
Some 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 radiation
1) Alpha (?) an atom decays into a new atom
and emits an alpha particle (2 protons and 2
______ the nucleus of a ______ atom)
Unstable nucleus
New nucleus
Alpha particle
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.
Beta particle
Unstable nucleus
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.
Words frequency, proton, energy, neutrons,
helium, beta
Unstable nucleus
New nucleus
Gamma radiation
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Changes in Mass and Proton Number
Alpha decay
Beta decay
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Uses 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 2
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Uses of radioactivity 3
Smoke detectors
Alarm
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Uses of Radioactivity 4 - Treating Cancer
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 life
The decay of radioisotopes can be used to measure
the materials age. The HALF-LIFE of an atom is
the time taken for HALF of the radioisotopes in a
sample to decay
After 3 half lives another 2 have decayed (14
altogether)
After 2 half lives another half have decayed (12
altogether)
After 1 half life half have decayed (thats 8)
At start there are 16 radioisotopes
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A radioactive decay graph
Count




Time
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Dating materials using half-lives
Question 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.
Answer The sample was originally completely
uranium
of the sample was uranium
Now 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 lead
So 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.
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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 Radiation
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Uses of radioisotopes - tracers
A tracer is a small amount of radioactive
material used to detect things, e.g. a leak in a
pipe
The radiation from the radioactive source is
picked up above the ground, enabling the leak in
the pipe to be detected.
Tracers can also be used to develop better plant
fertilisers and in medicine to detect tumours
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Nuclear power stations
These work by using nuclear fission reactions
using uranium
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Nuclear fission
New nuclei (e.g. barium and krypton)
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Chain reactions
Each fission reaction releases neutrons that are
used in further reactions.