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Question 1

State the electricity equation involving Charge, Current and Time.

Answer 1

Charge(Q) = Current(I) x Time(t)

Question 2

Describe current?(3)

Answer 2

Current is the flow of electric charge around the circuit. In metals, current is caused by a flow of electrons. It is measured in Amperes(A).

Question 3

Describe potential difference?(2)

Answer 3

Potential difference or voltage is the driving force that pushes the charge around. It is measured in Volts(V).
The volt is a joule per coulomb.

Question 4

Describe resistance?

Answer 4

Anything that slows down the flow. Measured in Ohms.

Question 5

State resistance equation.

Answer 5

Potential difference(V) = Current(I) x Resistance(R)

Question 6

What are two things that resistance depends on?1+2

Answer 6

Thickness - The number of electrons that can pass through depends on cross section area.
Length - The longer the length of a wire the more resistance.

Question 7

What are two other things that resistance depends on?3+4

Answer 7

Material - Insulators and conductors, silver is the best conductor.
Temperature - The more temperature the more resistance because lattice vibrations make it harder for electrons to flow.

Question 8

State Kirchhoff’s 1st Law.

Answer 8

At any junction the sum of current entering = the sum of current leaving.

Question 9

State Kirchhoff’s 2nd Law.

Answer 9

Around any closed loop the sum of voltage across the components is equal to the voltage supplied by the power source.

Question 10

Describe current and voltage in a series circuit?

Answer 10

Current is the same at any point in a series circuit. Voltage is shared across the circuit.

Question 11

Describe current and voltage in a parallel circuit?

Answer 11

Current is shared across the circuit. Voltage is the same across all components.

Question 12

State the electrical energy transferred equations.(2)

Answer 12

Energy transferred(E) = charge moved(Q) x potential difference(V).
Energy transferred(E) = current(I) x volts(V) x time(t)

Question 13

Describe the I-V graph of resistors and wires?

Answer 13

Current is directly proportional to potential difference. The graph is linear because it’s a straight line.

Question 14

Describe the I-V graph of lamps?

Answer 14

The I-V graphs are curved. The graph is non-linear because it’s curved.

Question 15

Describe the I-V graph for diodes?

Answer 15

Current only flows through one direction therefore flat line on one half and a curve on the other half.

Question 16

How do LDRs change in resistance and what are they used in?

Answer 16

In bright light the resistance falls, in darkness the resistance is highest. They are used for night lights, burglar detectors and outdoor lighting.

Question 17

How do Thermistors change in resistance and what are they used for?

Answer 17

In hot conditions the resistance drops, in cool conditions the resistance goes up. Thermistors are used in car engine temperature sensors and electronic thermostats.

Question 18

State the equation linking Energy transferred, Power and Time.

Answer 18

Energy transferred(J) = Power(W) x Time(s)

Question 19

State the electrical power equation.

Answer 19

Electrical power(W) = Current(I) x Potential difference(V)

Question 20

What are the two types of electricity supply?

Answer 20

Alternating(a.c.) and direct currents(d.c.)

Question 21

What type of electricity is the UK mains supply?(2)

Answer 21

It is an a.c. supply at an average of 230V but fluctuates between -330 and 330V.
The frequency of the supply is 50Hz.

Question 22

What type of electricity are batteries?

Answer 22

Cells and batteries supply d.c.

Question 23

In an electrical appliance connected to the mains, what is the blue wire for?

Answer 23

The blue wire is the neutral wire that completes the circuit it is around 0V.

Question 24

In an electrical appliance connected to the mains, what is the brown wire for?

Answer 24

The brown wire is the live wire. This carries the voltage and is around 230V.

Question 25

In an electrical appliance connected to the mains, what is the green/yellow wire for?

Answer 25

This is the Earth wire. This carries away the current if something goes wrong and stops the appliance casing becoming live. It is 0V.

Question 26

What is the difference between fuses and circuit breakers?

Answer 26

Circuit breakers turn off a circuit quicker than a fuse and also don’t need to be replaced as often but are more expensive.

Question 27

Why does resistance increase with temperature for a resistor?

Answer 27

Electrons travelling through a conductor find it harder to travel through the conductor if the atoms are not a fixed point; heated up.

Question 28

Describe ammeters?

Answer 28

Ammeters measure current and are connected in series with the circuit. Ideally ammeters should have no resistance so that the current is not affected.

Question 29

Describe voltmeters?

Answer 29

Voltmeters measure voltage and are connected in parallel with the circuit. Ideally voltmeters should have infinite resistance so that electrons do not flow down the path of the voltmeter.

Question 30

State two advantages of the heating effect in a circuit?

Answer 30

1. Fuses rely on the heating effect so that if a circuit has too much current they melt and break the circuit so its not dangerous.
2. Toasters and bulbs use the heat of an electric circuit to function.

Question 31

State two disadvantages of the heating affect in a circuit?

Answer 31

1. Heating in a component reduces its efficiency generally because less energy is transferred to useful energy stores.
2. If the temperature is too high components can melt and break and stop working all-together.

Question 32

What is double insulation and earthing?(2)

Answer 32

Insulating an appliance with plastic coating, ie a plastic iPhone charger, is said to be double insulated. It is not earthed because even it the appliance gets charged, plastic does not conduct electricity so theoretically it is not electrically dangerous.
Earthing a component is connected the appliance to the ground, so that the fault current flows to earth rather than through the appliance.