Electricity

Question 1

What is the current?

Answer 1

Current is the rate of movement of charge around a circuit

Question 2

In which direction does conventional current flow?

Answer 2

From the positive terminal of the power supply to the negative terminal

Question 3

What is the relationship between current, charge and time?

Answer 3

Charge = current x time
C coulombs = A amps x S seconds

Question 4

Name some items that can be used to protect the device or the user in a range of domestic electrical appliances.

Answer 4

Insulation, earthing, fuses, circuit breakers

Question 5

How does a circuit breaker work?

Answer 5

It interrupts the electrical current when it exceeds its design limitations

Question 6

How does a fuse work?

Answer 6

The fuse breaks the circuit if a fault in an appliance causes too much current to flow

Question 7

How does earthing work?

Answer 7

Earthing is used to protect you from an electric shock. It does this by providing a path (a protective conductor) for a fault current to flow to earth.

Question 8

How does electrical insulation work?

Answer 8

The atoms in insulators have tightly bound electrons that are static and do not move throughout the material. This means the current cannot easily pass through, which stops you from getting an electrical shock.

Question 9

How does double insulation work?

Answer 9

It consists of an extra layer of supplementary insulation over the basic insulation.

Question 10

Why does a current in a resistor result in the electrical transfer of energy and an increase in temperature?

Answer 10

If a current flows through a resistor, the resistor will heat up. Electrons collide with ions in the lattice of the resistor. As the electrons bump into the ions, energy is transferred causing the ions to vibrate and heat up.

Question 11

Where are resistors used in domestic contexts?

Answer 11

Heaters, toasters, microwaves etc

Question 12

What is the relationship between power current and voltage?

Answer 12

Power = current x voltage
P = I x V

Question 13

How do you know what size Fuse to use in an electrical appliance?

Answer 13

Once the current is known the next highest fuse rating is chosen.

Question 14

The relationship between current, voltage and resistance is expressed by which law?

Answer 14

Ohms law

Question 15

What is ohms law?

Answer 15

This states that the current flowing in a circuit is directly proportional to the applied voltage and inversely proportional to the resistance of the circuit,

Question 16

How do you investigate how current varies with voltage for a metal filament lamp?

Answer 16

Set up a circuit. Set up a circuit with a cell, an ammeter, variable resistor and a filament lamp in series.
Alter the current. Change the current in the circuit by moving the variable resistor.
Record values for current and voltage for a given resistance.
Repeat step 3 two more times.

Question 17

What is the effect of changing resistance on the current in a circuit?

Answer 17

If resistance increases, it becomes harder for the electricity to move through the component and therefore the rate of the flow of electricity (i.e. the current) decreases.

Question 18

Describe the variation of resistance of light dependent resistance with illumination

Answer 18

Their resistance decreases as the light intensity increases. In the dark and at low light levels, the resistance of an LDR is high, and little current can flow through it. In bright light, the resistance of an LDR is low, and more current can flow through it.

Question 19

Describe the variation of resistance of thermistors with temperature

Answer 19

Their resistance decreases as the temperature increases. At low temperatures, the resistance of a thermistor is high, and little current can flow through them. At high temperatures, the resistance of a thermistor is low, and more current can flow through them.

Question 20

What is the relationship between voltage current and resistance?

Answer 20

Voltage = current x resistance
V = I x R