# P4-6

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• Created by: xxemilyxx
• Created on: 17-06-14 11:11
How are explosions of static charged objects be prevented?
Earthing the charged objects - connecting it to the ground by a conductor.
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How does anti static spray work?
It makes the surface of a charged object conductive do there's an easy route for static charges to go to the ground.
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How does a precipitator work?
A metal grid makes the dust particles negatively charged so they repel electrons on earthed metal plates which makes them positively charged so the dust is attracted to them and stick there where they can be knocked off.
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What is a current?
Flow of electrons (amps)
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What is voltage?
The driving force that pushes the current round the circuit. (volts)
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If the voltage increases
More current will flow
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If the resistance increase
Less current will flow
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What is the live wire?
It's brown and carries the voltage, alternating between - and + of about 230V
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What is the neutral wire?
It's blue and completes the circuit, the electricity goes out of the plug through it, always at 0V
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What is the earth wire?
It's green/yellow and works with a fuse for safety. If the live wire touches the metal case the current flows through the case and out through the earth wire.
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What's a rheostat?
A variable resistor
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Resistance+
Voltage/current
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Where is a voltmeter placed?
Parallel around the component.
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Where is an ammeter placed?
In series with the component.
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What are longitudinal waves?
Vibrations in the same direction that the wave is travelling.
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What are compressions?
Parts of a longitudinal wave where it is under high pressure (lots of particles)
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What are rarefactions?
Parts under low pressure (fewer particles)
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What are transverse waves?
Vibrations are at 90 degrees to the direction of travel.
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How does ultrasound get rid of kidney stones?
Ultrasound beam concentrates high energy waves at the kidney stone, turning it into sand like particles that can pass out of the body in urine.
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How are ultrasound waves used for body scanning?
They can pass through the body but when they meet a boundary between two different media some of the wave is reflected back. The timing and distribution of these 'echos' are processed by a computer
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Why is ultrasound better than x-rays?
Ultrasound is good at imaging soft tissue whereas x-rays pass easily through skin and soft tissue so are only used to make images of hard things. X-rays are ionising radiation that can damage living cells and cause cancer is too high a dose is used.
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When atoms with unstable nuclei decay at random and give out either alpha, beta or gamma then change into a new element. Gamma is given out after alpha or beta if there is some extra energy. Gamma has no mass or charge.
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What is an alpha particle?
A helium nucleus with a mass of 4 and a charge of +2. so it has 2 protons and 2 neutrons.
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What is a beta particle?
A fast moving electron with no mass and a charge of -1. When a nucleus emits a beta particle the atomic number increases by 1.
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What is half life?
The time it takes for half of the radioactive nuclei to decay.
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X-rays + Gamma transfer energy to electrons so they have enough energy to escape from the atom, ionising it, leaving it positively charged. Beta and alpha particles remove electrons from atoms they collide with, Beta can also stick making it negative
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What do low doses of this do?
Cause minor damage to the cell that can cause mutant cells that divide uncontrollably causing cancer.
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What do high doses do?
Kill cells, if a lot of cells get blasted at once it causes radiation sickness.
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Which radiation is the most dangerous outside of the body?
Beta and Gamma as they can pass through the skin and get inside delicate organs, whereas alpha can't.
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Which is most dangerous inside the body?
Alpha as they do all their damage in a localised area, whereas beta and gamma are less ionising and mostly pass straight out of the body without much damage.
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From firing high speed electrons at a heavy metal (tungsten). The thicker or denser the matter the more x-ray that's absorbed , this varying amount of radiation absorbed makes the image.
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Gamma rays are focused on the tumour using a wide beam and is rotated around the patient to minimises exposure of normal cells and damage on the rest of the body.
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How do smoke detectors work?
A weak alpha source is placed between two electrodes which causes ionisation of the air particles below that allow a current to flow between the electrodes. Smoke particles are hit by the alpha which causes less ionisation so the current is reduced.
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Measuring the amount of radioactive isotope left in a sample and comparing it to the half life to see how long it has been around.
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When things die gas exchange stops and so carbon-14 is trapped inside and gradually decays with a half-life of 5730 years.By measuring the proportion of carbon-14 left you can calculate how long ago it was living material.
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What is nuclear fission?
Splitting up uranium atoms so energy is released to heat water.
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How does a nuclear reactor work?
Free neutrons make the uranium unstable and split causing the temperature in the reactor to rise.
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How do control rods control the reaction?
They are made of boron and limit the rate of fission by absorbing excess neutrons.
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What is nuclear fusion?
In stars. The joining of small atomic nuclei to create a larger nucleus, releasing lots of energy. little radioactive waste and uses hydrogen. Only at high pressures and temperatures.
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What are scalar quantities?
Don't have direction, only a number. Speed, mass, temp, time, length
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What are vector quantities?
They have a direction. Velocity, force, displacement, acceleration, momentum.
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How do you work out resultant velocity?
If they are opposite, add. if no use p
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What is Newton's third law of motion?
If object A exerts a force on object B, then B exerts and equal and opposite force on A.
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In (m1 X u1) +(m2 X u2) = (m1 + m2) X V what do the letters stand for?
M= mass, U=velocity, V= velocity of combined objects
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Change in momentum =
mass X change in velocity
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What force causes orbits?
Centripetal
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If you multiply the distance from a planet by x ....
The gravitational force will decrease by x^2
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What satellites are geostationary?
Communication - they stay over the same point on Earth.
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What do weather and spying satellites do?
They have low orbits and pass over both poles whilst Earth rotates beneath it.
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What waves are reflected off the ionosphere?
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What happens to radio and microwaves between 30MHz and 30GHz?
Pass straight through the ionosphere
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What happens to waves above 30GHz?
Rain and dust absorb and scatter the waves, making them weaker.
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The smaller the gap..
the more diffraction
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What does polarising do?
You can polarise transverse waves like light. A polarising filter only lets through vibrations in one direction. When light is reflected from water it is partly polarised.
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What is refraction?
When waves change direction, due to change in speed as they enter a different medium .
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When the speed decreaces it...
bends towards the normal.
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Which light slows down the least?
Red light so it is refracted the least.
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TIR only happens when...
The light travels into a more dense medium with a higher refractive index.
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If the angle of incidence is less that the critical angle...
Most of the light passes out into air but some is internally reflected.
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If it is equal...
The ray travels along the surface and there's a bit of internal reflection.
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If the angle of incidence is greater than the critical angle...
Total internal reflection.
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The higher the refractive index...
the lower the critical angle.
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What is a real image?
When light from an object forms an image on a 'screen'
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What is a converging lense?
Convex, it focuses the light onto a point.
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In a LDR, the higher the light intensity shining on it...
the lower the resistance.
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In a Thermistor, the higher the temperature...
the lower the resistance.
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What are the parts of a transistor?
Base- if no current is applied to the base it stops current flowing through the rest of the transistor. Collector- Current flows into the transistor through it. Emitter- current flows out of it.
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What shape is a 'Not' gate?
A triangle with a circle on the tip
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What shape is an 'Or' gate?
A curved arrow.
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What shape is an 'And' gate?
Like a 'D'
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Where is a LED placed?
In series with a resister to prevent the current from being too large.
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What is a relay switch?
The low current circuit turns on the electromagnet, closing the iron contact which is on a pivot making the high current circuit complete.
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What is a solenoid?
A coil of wire.
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What is electromagnetic induction?
The creation of a voltage in a wire which is experiencing a change in magnetic field.
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What are isolating transformers?
They have the same number of turns in both primary and secondary coils. They minimise the risk of getting electrocuted, as you can't touch the live parts that are connected to the Earth.
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What are diodes?
They only allow current to flow in one direction. They are made from semiconductors such as silicon.
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What are the semiconductor diodes made of?
Silicon diodes has an n-type semiconductor which has extra free electrons and a p-type semiconductor which has fewer free electrons than normal so contains empty spaces called 'holes'
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How do they work?
When there is no voltage the holes and electrons recombine to create no holes or free electrons which act as an electrical insulator. When voltage flows in the right direction the holes and electrons have enough energy to cross the insulating region.
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What is full-wave rectification?
Using a bridge circuit of 4 diodes.
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What is a capacitor?
It stores charge and smooths circuits.
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## Other cards in this set

### Card 2

#### Front

How does anti static spray work?

#### Back

It makes the surface of a charged object conductive do there's an easy route for static charges to go to the ground.

### Card 3

#### Front

How does a precipitator work?

### Card 4

#### Front

What is a current?

What is voltage?