OCR Physics Module P4 RADIATION FOR LIFE
P4a Sparks
Static electric charge
Charge types
Electrostatic forces
Nuisance of static electricity
Dangers of static electricity
Discharge prevention
Reducing electric shock
Reducing static charge
P4b Uses of Electrostatics
Uses of static electricity
Defibrillator
Dust precipitator
Paint spraying
P4c Safe Electricals
Electric circuit
insulating materials can become charged when rubbed with another insulating material; charging caused by the
transfer of electrons
positive = lack of electrons; negative = excess of electrons
like charges repel and unlike charges attract; dust etc attracted; caused by the transfer of electrons
dirt and dust attracted to insulators (plastic containers, TV monitors etc); causing clothing to “cling”
ignition of explosive atmospheres e.g. inflammable gases/vapours or with high concentrations of oxygen;
in situations where large quantities of charge could flow through the body to earth
earth lorries containing inflammable gases and liquids and powders before unloading
chance reduced by: correct earthing; use of insulating mats; using shoes with insulating soles
anti-static sprays, liquids and cloths
restarting a heart when it has stopped (defibrillator); photocopiers/laser printers (detailed structural knowledge
not required); removing dust from smoke in chimneys; paint spraying
paddles charged; good electrical contact with patient’s chest; charge passed through patient to make heart
contract; care taken not to shock operator
to remove smoke particles etc from chimneys: metal plates/grids put into chimneys; connected to a high PD;
dust particles attracted to plate/grid; dust particles are attracted together to form larger particles; dust falls back
down chimney when particles are heavy enough
spray gun charged; paint particles charged; repel giving fine spray; object charged oppositely to paint; attracts
paint; even coat, less waste, shadows painted
Re-settable fuses
Protection
“Double insulated” appliances
Explain the behaviour of simple circuits in terms of the flow of electric charge; a complete loop is required for a
circuit to work; an earthed conductor cannot become live
used to change the current in a circuit; fixed or variable (rheostat)
relationships between current, potential difference (pd) and resistance; for a given resistor, current increases as
Pd increases and vice versa; for a fixed pd, current decreases as resistance increases and vice versa
resistance (Ω) = voltage (V) ÷ current (A)
live (carries the high voltage); neutral (the second wire to complete the circuit); earth (a safety wire to stop the
Appliance becoming live)
protects an appliance if the appliance develops a fault; too large a current causes the fuse melt; preventing flow
of current; prevents flex overheating and causing fire; prevents further damage to appliance
fuses/circuit breakers
wire fuse and earthing protects people; prevents electric shock; appliance casing not become live
not need earthing: case of appliance is a non-conductor and cannot become live
P4d Ultrasound
Ultrasound
Longitudinal wave
Transverse wave
Longitudinal wave properties
Frequency of ultrasound
Uses of ultrasound
Ultrasound or x-rays
example of longitudinal wave
wave disturbances (oscillations) go in the direction of the wave motion
wave disturbances (oscillations) go across/perpendicular to the direction of the wave motion
amplitude; wavelength; frequency; compression; rarefaction
higher than the upper threshold of human hearing
body scans (reflections from different layers); breaking down kidney and other stones
ultrasound is able to produce images of soft tissue; ultrasound does not damage living cells
Resistors
Resistance
Resistance equation
Wiring
Fuse
P4e Treatment
Nuclear radiation
Radiographer
X-rays and gamma rays
Gamma rays
X-rays
Gamma rays
Penetration
Cancer treatment
Tracers
P4f What is radioactivity?
Radioactivity
Radioactive substance
Half-life
4
Alpha (α) He 2
Beta (β)
Gamma (γ)
Atomic (proton) number
Mass number
Alpha (α) emitter
Beta (β) emitter
Equations
used in medicine
person in hospitals who takes x-rays and uses radiation
electromagnetic waves; very high frequency; very short wavelength
given out from the nucleus of certain radioactive materials
made by firing high speed electrons at metal targets; easy to switch on/off so easier to control than gamma rays
treat cancer; sterilize hospital equipment
alpha radiation cannot pass through skin; beta and gamma radiation can pass through skin
gamma rays focused on tumour; wide beam used; rotated round the patient with tumour at centre; limiting
damage to non-cancerous tissue
beta or gamma emitter; drunk/eaten/ingested/injected into the body; allowed to spread through the body;
followed on the outside by a radiation detector
measured by the number of nuclear decays emitted per second; decreases with time; comes from the nucleus
of an atom that is unstable
decays naturally and dives out nuclear radiation in the form of alpha (α), beta (β) and gamma (γ)
time taken for radioactivity to halve
alpha particle is a helium nucleus;
beta particle is a fast moving electron
gamma ray is an electromagnetic wave
number of protons in the nucleus
number of protons and neutrons in the nucleus
mass number decreases by 4; nucleus has two less neutrons; nucleus has two less protons; atomic number
decreases by 2; new element formed
mass number is unchanged; nucleus has one less neutron; nucleus has one more proton; atomic number
increases by one
construct and balance simple equations in terms of mass numbers and atomic numbers to represent alpha and
beta decay
example:
P4g Use of radioisotopes
Background radiation
Background radiation – causes
Tracers – uses
Tracers – how used in industry
Smoke detector
Dating rocks
Carbon-14 dating
Carbon-14 dating – measurements
P4h Fission
Nuclear power stations
Electricity production
Fission of uranium
Chain reaction
Chain reaction – of uranium
Chain reaction – control
Nuclear waste from fission
background radiation is in the environment which is always present
radioactive substances in rocks and soil; cosmic rays; nuclear testing; waste products – industry; hospitals
track dispersal of waste; find leaks/blockages in underground pipes; find the route of underground pipes
radioactive material put into pipe; gamma source used so that it can penetrate to the surface; progress tracked
with detector above ground; leak/blockage shown by reduction/no radioactivity after this point
α particle source; α particles cause ionisation; detected by sensor; smoke particles block α particles; sensor
detects lack of ionisation; sets off alarm
radioactive dating of rocks depends on the calculation of the uranium/lead ratio
measurements from radioactive carbon can be used to find the date of old materials
the amount of Carbon 14 in the air has not changed for thousands of years; when an object dies (e.g. wood)
gas exchange with the air stops; as the Carbon 14 in the wood decays the activity of the sample decreases;
the ratio of current activity from living matter to the activity of the sample leads to a reasonably accurate date
use uranium as a fuel
nuclear reaction (source of thermal energy); boiler (water to steam); pressure of steam (turns the turbine);
production of electricity (turbine turns generator)
uranium nucleus hit by neutron; nucleus splits [fission]; matter converted to energy; E=mc2; energy released
decay of uranium can be a chain reaction; controlled in nuclear reactor (uranium); uncontrolled in nuclear bomb
(uranium/plutonium)
when a uranium nucleus splits, more than one neutron is given out; these neutrons can cause further uranium
nuclei to split
scientists stop nuclear reactions going out of control; rods (carbon/boron) placed in the reactor; absorb some of
the neutrons; allow enough neutrons to remain to keep the process operating
spent nuclear fuel; materials made radioactive by putting them into a nuclear reactor (absorb extra neutrons)