Charge and Current

Question 1

Current is…

Answer 1

The flow of charge round a circuit.

Question 2

Voltage acts like a …. that pushes the current round the circuit.

Answer 2

Force.

Question 3

Resistance…

Answer 3

Restricts the flow of current round the circuit.

Question 4

Current is measured in…
Voltage is measured in…
Resistance is measured in…

Answer 4

Amperes, volts, ohms.

Question 5

The wires in an electric circuit are full of … that are free to move.

Answer 5

Charges

Question 6

Describe energy changes in a circuit.

Answer 6

The battery transfers chemical energy into electricity which is transferred to the charges travelling around the circuit. These charges transfer the energy to the components. Potential difference describes the energy transferred to or from each unit charge between two places. During this process, work is done. Work done on the charge equals work done by the charge.

Question 7

Why does no current flow when a switch is open?

Answer 7

The circuit is not complete so the current cannot flow.

Question 8

Energy is transferred to an appliance when ….. ….. flows through it. The …. at which an appliance transfers …. from the charge is the power rating.

Answer 8

Electric charge, rate, energy.

Question 9

How can the current be increased or decreased with a constant voltage?

Answer 9

To increase the current, reduce the resistance. To reduce current, increase the resistance.

Question 10

What is the formula for power?

Answer 10

Power (W) = Voltage (V) x current (A)

Question 11

An object has a high power when…

Answer 11

It transfers lots of energy in a small amount of time. Ie - a power of 1kW describes 1kW of energy being transferred each second.

Question 12

What does a cell do?

Answer 12

Provide the charge with a ‘push.’

Question 13

What does a variable resistor do?

Answer 13

Alter the current by changing resistance. This is shown by a rectangle with an arrow pointing to the upper right across it.

Question 14

What does a component do?

Answer 14

This is tested in a standard circuit.

Question 15

What do the voltmeter and ammeter do?

Answer 15

The voltmeter measures the potential difference across a component, and the ammeter measures the current in a series circuit.

Question 16

Voltage, (or …..), measures how much …. is transferred to or from the charge as it moves between two points. The …. transfers …. to the charge and ….. transfer it away from the charge. A voltmeter must be connected in…..

Answer 16

Potential difference, energy, battery, energy, components, parallel.

Question 17

What is the formula for charge, (coulombs)?

Answer 17

Charge (C) = Current (A) x time (s)

Question 18

When a current of 1A flows, what does this mean?

Answer 18

A charge of 1C is travelling at one point of the circuit per second.

Question 19

What is the charge of one electron?

Answer 19

1.6 x 10^-19

Question 20

Why are metals good conductors?

Answer 20

They have lots of free electrons outside the electron shells of the metal ions. These are free to move around the circuit, allowing for charge to flow when a voltage is supplied and energy is transferred from the battery to each unit charge.

Question 21

What are semi-conductors?

Answer 21

These are materials which contain some free electrons. The amount depends on the temperature of the material, but these are less effective than normal conductors.

Question 22

What are insulators?

Answer 22

These are materials with no free electrons, which means that charge, and so current, cannot flow in the circuit when a voltage is supplied.