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32 Cards in this Set
- Front
- Back
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What happens when two insulating materials are rubbed together? |
Electrons will be rubbed off one and put on to the other
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What charge is given when two insulating materials are rubbed together?
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Positive on one that has lost electrons/due to lack of electrons
Negatie charge on the one that has gained electrons/excess of electrons |
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What does the direction of the electrons transferred depend on?
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The two materials
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What can happen if enough static charge builds up?
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It can suddenly move which can cause sparks or shocks that can be dangerous
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Give 3 examples of when electricity can be a nuisance
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1. Attracting dust: objects that are made out of insulators eg. TV
2. Clothing clings and crackles: little sparks/shocks 3. Shocks from door handles: walk on a nylon carpet with insulating soles |
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Give 2 ways that electricity can be dangerous
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1. A lot of charge built up on clothes can cause a spark and is dangerous if near inflammable gases or fuel fumes
2. Fuel filling: as fuel flows out of a filler pipe, the static can build up, can lead to a spark and cause an explosion |
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How can dangerous sparks be prevented?
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Connecting a charged object to the ground using a conductor = earthing
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How do anti-static sprays work?
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By making the surface of a charged object conductive = provides an easy path for the charges to move away
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How do paint-sprayers work?
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- The spray gun and object are oppositely charged
- Each paint drop repels making a very fine spray - The object attracts the paint - Gives an even coat, hardly any paint is wasted and no shadows |
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How do dust-precipitators work?
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- Smoke particles meet wire grid/rods with high voltage and negative charge
- Dust gain electrons = negatively charged - Dust induces a charge on the earthed metal plates and are attracted to them where they stick together to form larger particles - When heavy enough they fall |
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How do defibrillators work?
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- Electric shock to make stopped heart, beat again
- Two paddles placed firmly on patients chest for good electrical contact and is then charged up - Everyone moves away except operator, which has insulated handles (only patient gets shock) - Charge passes through paddles to make heart contract |
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What is the current?
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The flow of electrical charge around a circuit (flow of electrons)
- Measure in amps (A) |
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What is the voltage?
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The driving force that pushes the current round
- Measure in voltage (V) |
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What is resistance?
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Anything that slows the flow down
- Measured in ohms |
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What happens to the current if you increase the voltage?
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The more current will flow
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What happens to the current if you increase the resistance?
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The less current will flow
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What colour is the live wire? What does it carry?
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Brown
Carries the voltage |
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What colour is the neutral wire? What does it do?
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Blue
Completes the circuit - electricity flows in through live wire, and out of neutral |
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What colour is the earth wire? What is its purpose?
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Green and yellow
For safety |
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What is meant when an appliance is double insulated?
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It has a casing that's non-conductive (eg. plastic)
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Why does a double insulated appliance not need an earth wire?
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It cannot become live
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What could happen if there is an electrical surge?
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It could damage the appliances connected to the main supply
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Name two ways devices are protected from electrical surges
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1. Fuses
2. Circuit breaker |
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What is a fuse?
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A fuse is used to protect appliances from a current which is too high
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How does a fuse work?
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- The friction (between electrons and atoms of conductor) causes heat, the more current the hotter the fuse gets
- Contain pieces of conductor that melt if the current is too high = breaking the circuit |
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How does a fuse reduce the risk of a fire?
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- Too large current = melts
- Prevents large current from flowing - Stops cable over-heating and causing fire |
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What is a circuit breaker?
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A resettable fuse. When the circuit breaker trips it switches off the circuit but does not require a new piece of wire to make it work again
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What does a variable resistor consist of?
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Wire and a marker
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How is the resistance changed in a circuit using a variable resistor?
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The length of the wire is changed by moving the marker
Longer wire = higher resistance = lower current Shorter wire = lower resistance = higher current |
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What other thing can the amount of resistance depend on?
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The thickness of the wire
Thicker wire = less resistance = higher current Thinner wire = high resistance = lower current |
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How do you calculate resistance?
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Resistance = Voltage / Current
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What is potential difference?
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The difference in voltage between two points in a circuit
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