# OCR Gateway P4 revision

• Created by: charlotte
• Created on: 15-06-13 13:25
describe the movement of electrons in static electricity
a positive/negative charge is caused by lack/excess of electrons
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like charges...
repel
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unlike charges...
attract
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how can static electricity be dangerous?
explosions could occur due to inflammable gases/vapours with high concentrations of oxygen. large quantities of charge could flow through the body to the earth
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how to reduce the chance of getting an electric shock
correct earthing, use of insulating mats, shoes with insulating soles
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why do lorries containing inflammable gases/liquids need earthing?
if an object (likely to become charged) is connected to earth, any build up of it immediately flows down the earth wire, reducing risk of a shock
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how do anti-static sprays. liquids & cloths reduce static electricity problems?
made from conducting materials which carry away charge, preventing a build up
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how to restart the heart using a defibrillator
paddles are charged, good electrical contact with patients chest, charge is passed through to make the heart contract & care is taken not to shock operator
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how can static electricity be used by electrostatic dust precipitators to remove smoke particles
metal plates put into chimneys, connected to high voltage supply, dust particles are attracted and form larger particles, when heavy enough they fall back down chimney
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how is static electricity used for paint spraying?
spray gun and paint particles are charged, paint particles repel each other giving it a fine spray, object charged oppositely to paint, attracts paint, even coat, less waste
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explain simple circuits
electric current is a flow of charge carried by negatively charged electrons, they flow in the opposite direction to the conventional current
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how do variable resistors change current in a circuit?
change the resistance
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relationships between current, potential difference & resistance
for a given resistor, current increases as pd increases. for a fixed pd, current decreases as resistance increases
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equation for resistance
voltage / current
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functions of each wire in a plug
live - carries high voltage. neutral - 2nd wire to complete the circuit. earth- safety wire to stop appliance becoming live
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how does a wire fuse work?
if current becomes to large, wire fuse melts, breaking the circuit
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why do double insulated appliances not need earthing?
case of appliance is a non conductor and cannot become live
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features of longitudinal waves
compression, rarefaction, amplitude, wavelength, frequency
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applications of ultrasound
body scans & breaking down kidney stones
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how does ultrasound break down things such as kidney stones?
high powered beam is directed at stones, the energy breaks the stones into smaller pieces, which are then excreted
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how does ultrasound work in body scans?
at each boundary between different tissues some ultrasound is reflected and the rest is transmitted, the returning echos are recorded and used to build up an image of the internal structure
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adv of ultrasounds over x rays
able to produce images of soft tissue, no damage to living cells
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firing high speed electrons at metal targets
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what are and how are they used as tracers in the body?
beta or gamma emmiters are drunk/eaten/injected into body, allowed to spread through. followed on the outside by radiation dectector
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how are radioactive sources used to treat cancer?
gamma rays focused on tumor, wide beam used, rotated round the patient, limiting damage to non cancerous tissue
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similarity/difference between gamma and x rays
similar wavelengths, produced in different ways
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substances which are decaying naturally and releasing nuclear radiation in the form of alpha, beta & gamma
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what is half life of a radioisotope?
the average time taken for half the nuclei to decay
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what happens to a nucleus when an alpha particle is emitted?
mass no. decreases by 4, nucleus has 2 less protons/neutrons, atomic no. decreases by 2, new element is formed
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what happens to a nucleus when an beta particle is emitted?
mass no. unchanged, nucleus has one less neutron/more proton, atomic no. decreases by 1
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what is background radiation & what is it caused by?
ionising radiation that is always present in the enviroment caused by radioactive substances & cosmic rays from space
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uses of tracers
track dispersal of waste, find blockages in and the routes of underground pipes
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how are tracers used
radioactive material put into pipe, gamma source used to penetrate surface, progress tracked by an above ground detector & blockage shown by reduction after this point
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how is domestic electricity generated at nuclear power station?
nuclear reaction, produces heat & steam, turns a turbine and then a generator
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what happens to allow uranium to release energy
uranium nucleus hit by electron, causes nucleus to split
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## Other cards in this set

like charges...

repel

### Card 3

#### Front

unlike charges...

### Card 4

#### Front

how can static electricity be dangerous?

### Card 5

#### Front

how to reduce the chance of getting an electric shock