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32 Cards in this Set

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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
What charge is given when two insulating materials are rubbed together?
Positive on one that has lost electrons/due to lack of electrons
Negatie charge on the one that has gained electrons/excess of electrons
What does the direction of the electrons transferred depend on?
The two materials
What can happen if enough static charge builds up?
It can suddenly move which can cause sparks or shocks that can be dangerous
Give 3 examples of when electricity can be a nuisance
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
Give 2 ways that electricity can be dangerous
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
How can dangerous sparks be prevented?
Connecting a charged object to the ground using a conductor = earthing
How do anti-static sprays work?
By making the surface of a charged object conductive = provides an easy path for the charges to move away
How do paint-sprayers work?
- 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
How do dust-precipitators work?
- 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
How do defibrillators work?
- 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
What is the current?
The flow of electrical charge around a circuit (flow of electrons)
- Measure in amps (A)
What is the voltage?
The driving force that pushes the current round
- Measure in voltage (V)
What is resistance?
Anything that slows the flow down
- Measured in ohms
What happens to the current if you increase the voltage?
The more current will flow
What happens to the current if you increase the resistance?
The less current will flow
What colour is the live wire? What does it carry?
Carries the voltage
What colour is the neutral wire? What does it do?
Completes the circuit - electricity flows in through live wire, and out of neutral
What colour is the earth wire? What is its purpose?
Green and yellow
For safety
What is meant when an appliance is double insulated?
It has a casing that's non-conductive (eg. plastic)
Why does a double insulated appliance not need an earth wire?
It cannot become live
What could happen if there is an electrical surge?
It could damage the appliances connected to the main supply
Name two ways devices are protected from electrical surges
1. Fuses
2. Circuit breaker
What is a fuse?
A fuse is used to protect appliances from a current which is too high
How does a fuse work?
- 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
How does a fuse reduce the risk of a fire?
- Too large current = melts
- Prevents large current from flowing
- Stops cable over-heating and causing fire
What is a circuit breaker?
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
What does a variable resistor consist of?
Wire and a marker
How is the resistance changed in a circuit using a variable resistor?
The length of the wire is changed by moving the marker
Longer wire = higher resistance = lower current
Shorter wire = lower resistance = higher current
What other thing can the amount of resistance depend on?
The thickness of the wire
Thicker wire = less resistance = higher current
Thinner wire = high resistance = lower current
How do you calculate resistance?
Resistance = Voltage / Current
What is potential difference?
The difference in voltage between two points in a circuit