electricity

Question 1

current

Answer 1

is measured in amperes (A).

Current is the rate of flow of charge. A current of 1 A means that 1 coulomb of charge flows past a point in a circuit every second. ( 1 A = 1 C s-1 )

Current is measured in a circuit using an ammeter which is placed in series with the component of interest in the circuit.

Question 2

Conventional current and electron flow

Answer 2

flows around a circuit from the positive (+) side of the cell to the negative (-). However the electrons are flowing around the circuit in the opposite direction from the negative (-) side of the cell to the positive (+).

Question 3

Circuit Symbols

Answer 3

Question 4

Charge

Answer 4

charge is measured in coulombs (C).

A single electron carries a charge of 1.6 x 10-19 C.

Question 5

Potential difference

Answer 5

Potential difference (V) – is measured in volts (V).

Potential difference is the work done per unit charge. A potential difference of 1 V means that 1 joule of work is done per coulomb of charge. ( 1 V = 1 J C-1) Potential difference in a circuit is measured using a voltmeter which is placed in parallel with the component of interest in the circuit.

Question 6

Resistance

Answer 6

Resistance (W) – is the ratio of potential difference across a component to the current flowing through it, it is measure in ohms (W

Question 7

circuit symbols for a resistor

Answer 7

Question 8

A resistor at constant temperature (ohmic conductor)

Answer 8

Current is directly proportional to potential difference. Doubling the potential difference doubles the current in the circuit. The resistance remains the same. Plotting a graph of potential difference against current gives a straight line passing through the origin (0,0).

Question 9

Ohm’s Law

Answer 9

The electrical current in a conductor is proportional to the potential difference applied to it provided the temperature remains the same.

Question 10

Measuring current and potential difference

Answer 10

Current is measure with an ammeter, ammeters are always connected in series with the component of interest.

Potential differences are measured using a voltmeter, voltmeters are connected in parallel with the component of interest.

By measuring the current and potential difference you can calculate the resistance.

Question 11

A Filament Lamp

Answer 11

Here the graph curves because as the filament heats it’s resistance goes up (the resistance of the filament is changing).