Electricity

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  • Created by: RGV17
  • Created on: 26-09-16 20:09
When does an object become charged?
When negatively charged electrons are added to or removed from it.
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What happens when two electrically charged objects are brought together?
If two objects have the same charge, they will repel and if they have opposite charges, they will attract each other.
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Why do plastic charged objects lose their charge against a metal object?
Electrical charges can move easily through metals.
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What is it called when electrical charges move through a metal or other electrical conductors?
An electrical current-measure of how much charge flows every second.
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What is the equation for working out the current?
I:Current in Amps(A)= Q: Charge in coulombs(C) divided by t= Time in seconds(s).
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What is the potential difference?
The work done between two points in a circuit per coulomb of charge passing through the circuit.
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What is the equation to work out potential difference?
V:p.d. in volts(V)= W: Work done in joules(J) divided by Q: Electrical charge in coulombs(C)
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What is a switch?
Turns the current in a circuit off and on.
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What is the cell and battery?
Creates a p.d. across a circuit. A battery is two or more cells.
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What is a diode?
Allows current to flow one way but not the other.
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What is a resistor?
Helps regulate current flow in a circuit.
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What is a fuse?
Breaks current flow if current gets too large.
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What is a voltmeter?
Measures p.d.
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What is an ammeter?
Measures current.
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What is a thermistor?
A temperature-dependent resistor.
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What is a LDR?
A light-dependent resistor.
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What affects current flow?
The amount of p.d. and the resistance of the components.
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What is Ohm's law?
V:Potential difference in volts(V)=I:Current in amps(A) multiplied by R:Resistance in ohms
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How can you plot a graph of potential difference against current?
By measuring the current flow at a range of p.d. values.
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What happens when a material obeys Ohm's law?
The current through it is directly proportional to the p.d. applied to it if the temperature of the material is held constant.
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How can you find the resistance of any component in a circuit?
By measuring the current flow through it and the p.d. across it. Resistance= p.d. divided by current
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How can thermistors be used?
It can be used to activate a switch for e.g. central heating because as it gets warmer the resistance of the thermistor gets lower.
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How can LDR's be used?
They can be used in circuits that turn on automatically at night because the brighter the light the lower the LDR's resistance and vice versa.
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What are non-ohmic devices?
Devices that don't follow Ohm's law, current and p.d. are not proportional to each other.
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What is an example of a non-ohmic device?
A filament bulb- the current that flows through the filament, will make it hotter and that increases the resistance of the filament, so it's more difficult for the current to flow.
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Why does the resistance change in a filament bulb?
The current is carried by electrons and they 'do work'. Therefore, the electrical energy is transferred through heating the filament.It makes the filament vibrate and get hotter, making it harder to make electrons to pass through-resistance increased
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How are current values recorded negative?
By changing the power supply round so the current flow the opposite way.
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Why does diodes not work the same both ways?
It only works like a one-way valve for electricity- allows current to pass in one direction but not the other.
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When is the resistance of a diode low and high?
Low-In its forward direction. High-In the reverse direction.
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What is the most efficient lighting?
LED's- lasts hundered of times longer than filament, used in torches and some car lights.
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What is in a series circuit?
Only one route for electric current to flow along; there are no branches or splits.
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What happens if all cells in a series circuit are facing the same way?
The total p.d. is all the individual cell p.d.s added together.
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What happens if the circuit in a series circuit is broken?
The current stops everywhere because the current in a series circuit is the same everywhere.
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What happens when the resistance in a circuit is large?
The current flow will be smaller.
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How do you find the total resistance in a circuit?
You add together the values of the resistors.
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How do you calculate the current from the total resistance and the p.d. of the battery?
I:Current(Amps) = V:p.d. divided by R:Total resistance
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What happens to the total p.d. in a series circuit?
It's shared between the components.
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How do you work out the p.d. across each resistor?
(Total p.d. multiplied by Resistance of Resistor) divided by Total Resistance
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What does a parallel circuit contain?
At least one place where the current splits into two or more separate currents.
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What happens to the p.d. in a parallel cirucit?
The p.d. is the same across each component while the current is different in different parts of the circuit.
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What happens to the current in a parallel circuit?
The current sets off from the cell and then splits in half when it comes to a fork in the circuit. Half the current flow through the top resistor and half through the bottom one. When they pass, they join up and form a big current again.
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What happens when the current splits?
The two smaller currents always add up to the larger one. When the join again, the current will be the same as before.
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How can you determine how the current splits?
Through the resistance of each branch- The larger the resistance, the smaller the current that flow down it.
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What does changing the flow in one branch of a parallel circuit affect?
It has no effect on the other branch(es) but it does affect the main current flow.
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What happens when bulbs are put in parallel?
The p.d. is the same across the branches but the resistance is greater because there might be more bulbs on one branch so the current is reduced.
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What is direct current(d.c.)?
When the current flows in one direction only from positive to negative.
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What is the advantage of d.c.?
Low-voltage electronic circuits can use it, so electronic devices can be portable.
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What is alternating current(a.c.)?
When the direction of the current changes many times per second.
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What is the frequency of the electrical supply in the U.K.?
50 Hertz.
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What is an advantage of a.c.?
Can be easily changed using transformers, over long distances the voltage is increase to reduce energy loss.
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What is a disadvantage of a.c.?
Many electrical appliances run on d.c., if it's run on the mains, the a.c. supply has to be changed into d.c.
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What does a cathode ray oscilloscope do?
It measures the voltage of an electrical supply.
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Why do appliances use the mains?
A cell would not be powerful enough for some appliances, the supply is continuous and it can recharge batteries.
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What is the structure of an electric cable?
Stranded copper wire. Coloured inner insulation. Outer insulation.
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Explain the properties of the stranded copper wire in electrical cables?
This is the core of the cable. Copper is a very good electrical conductor. The bundle of thin copper strands can be bent and coiled without breaking.
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Explain the properties of the coloured inner insulation in electrical cables?
The colour indicates which wire is which and insulates the copper from other wires within the cable.
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Explain the properties of the outer insulation in electrical cables?
This is stiffer and harder than the inner insulation. It provides strength and extra protection.
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What are plugs made out of?
The body is made from tough insulating plastic to protect the user from any electrical contacts. Connecting pins made from a conducting metal are designed to fit into holes in an electrical socket.
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What are the three connecting pins that most modern plugs have?
Live and neutral pins which connect to complete the electrical circuit and an earth pin.
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How should a plug be wired?
The live wire(brown) is connected to fuse which in turn is connected to the live pin. The neutral wire(blue) and is connected to the neutral pin. The earth wire(green and yellow) is connected to the earth pin.
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What are the rules when wiring a plug?
Check the correct colour is attached. Assure the wires aren't stretched. Assure the screws grip the wire firmly. No copper wire should be visible.The cable grip should hold the outer insulation firmly.The fuse should match the appliance power rating.
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What type of cable should an appliance need?
It depends on the power and its type of insulation.
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What can a faulty electrical appliance cause?
It might reduce the resistance of the circuit, so a larger current than normal might flow. Then it can catch fire. It can cause an electrical wire to touch a metal part which can cause an electric shock.
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What are the safety devices used to protect against faulty electrical appliances?
Fuse, earth wires and circuit breakers.
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What does a fuse do?
It breaks the electrical connection if the current gets above the fuse rating which is the maximum current it can hold. It contains a length of wire that melts if the current in a circuit gets too high.
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What does an earth wire do?
It's a low-resistance path for electric current to flow through, it's connected to the metal parts of an appliance. If there's a fault, then a large current flows along the earth wire, causing the fuse to blow and makes it safe.
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What if appliances have a plastic casing?
They don't need an earth wire because there are no metal parts that can become electrified. This is double-insulated, it uses a two-core cable as it doesn't need an earth wire.
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What does a circuit breaker do?
They're similar to fuses but they're more sensitive and operate faster.
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What does a residual current circuit breaker do(RCCBs)?
It works by sensing any difference in current between the live and neutral wires. In a normal circuit the current in both wires are the same. But if RCCB senses a difference, it disconnects the electricity(used in lawnmowers).
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What is the equation for measuring the power of a device(measuring how much energy it transfers per second)?
P:Power in watts(W)= E:Energy in joules(J) divided by t:Time in seconds(s).
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What is the equation for measuring the power of a device(measuring the current and the potential difference)?
P:Power in watts(W)= I:Current in amps(A) multiplied by V:Potential difference in volts(V).
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What is the equation for calculating the amount of charge flowing in a given time?
Q:Charge in coulombs(C)= I:Current in amps multiplied by t:Time in seconds(s).
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What does p.d. measure?
It's a measure of the 'electrical push'. As electrons move, they transfer energy and the harder they're pushed, the more energy is transferred.
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What does the amount of energy transferred by one coulomb of charge depend on?
It depends on the p.d. that pushes it.
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How do you calculate energy transferred?
E:Energy transferred in joules= V:p.d. in volts(V) multiplied by Q:Charge in coulombs(C).
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Card 2

Front

What happens when two electrically charged objects are brought together?

Back

If two objects have the same charge, they will repel and if they have opposite charges, they will attract each other.

Card 3

Front

Why do plastic charged objects lose their charge against a metal object?

Back

Preview of the front of card 3

Card 4

Front

What is it called when electrical charges move through a metal or other electrical conductors?

Back

Preview of the front of card 4

Card 5

Front

What is the equation for working out the current?

Back

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