# OCR Gateway Science B- P4: Radiation for life

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What does the law of electric charge state?
Objects with the same charge repel and objects with opposite charges attract
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How does a polythene rod become negatively charged when rubbed with a duster?
electrons are transferred from the duster to the rod
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How does an object have a positive or negative charge?
Positive- due to lack of electrons Negative- due to an excess of electrons
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How can electric shocks be avoided?
If an object is likely to become charged connect it to earth, In factories, operators stand on an insulating mat, shoes with insulating soles are worn, fuel tankers are connected by a conducting cable.
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What does a dust precipitator do?
Removes harmful particles from chimneys of factories and power stations that pollute the atmosphere
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How do dust precipitators work?
A metal grid is placed in the chimney and given a large charge from a high-voltage supply. Plates inside the chimney are earthed and given a opposite charge to the grid. As the particles pass the grid they gain the same charge and attract the plates.
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How is static electricity used in paint spraying?
The spray gun is charged positively and the object is charged negatively. Paint particles become positively charged and spread out as they repel each other. Paint is then attracted to the object and it gets an even coat with little paint wasted.
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What does a variable resistor do?
-Changes the resistance - Longer wires have more resistance and so do thinner wires
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What happens as voltage across a fixed resistor increases?
The current increases
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What happens as the resistance increases in a fixed power supply?
The current decreases
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What is the formula for Resistance and what is it measured in?
Resistance=Voltage/current measured in Ohms
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What does a live wire do?
Carries a high voltage around a house
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What does a neutral and earth wire do?
neutral wire- completes the circuit providing a return path for the current Earth wire- is connected to the case of an appliance to prevent it becoming live.
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What does a fuse and earth wire prevent?
Stops someone receiving and electric shock if they touch a faulty appliance.
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What is the formula for power?
Power= voltage x current
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What are the features of a longitudinal sound wave?
-Cant travel through a vacuum - Higher frequency or pitch means a smaller wavelength. -The more powerful the more energy is carried and a longer amplitude is the result.
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In a longitudinal wave are the vibrations of particles parallel or at right angles to the direction of the wave?
Parallel - Transverse waves are at right angles to the direction of the wave
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Why is ultrasound preferred instead of x-rays?
- ultrasound doesn't damage living cells and is able to produce images of soft tissue
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What is a half- life?
The average time for half the nuclei present to decay.
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What are the properties of an alpha particle?
Its positively charged, has a large mass, consists of 2 protons and 2 neutrons and is a helium nucleus
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What are the properties of a beta particle?
its negatively charged with a very small mass, It travels fast and is an electron
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Radioactive substances present in rocks and soils, Cosmic rays and man made sources including radioactive waste from industry and hospitals
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When does nuclear fission occur?
When a large unstable nucleus is split up and energy is released as heat.
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## Other cards in this set

### Card 2

#### Front

How does a polythene rod become negatively charged when rubbed with a duster?

#### Back

electrons are transferred from the duster to the rod

### Card 3

#### Front

How does an object have a positive or negative charge?

### Card 4

#### Front

How can electric shocks be avoided?

### Card 5

#### Front

What does a dust precipitator do?