P3.2 Simple circuits

Question 1

What is a series circuit?

Answer 1

A series circuit is one in which the same charge passes through all components, so the current through each component is the same.

Question 2

What is a parallel circuit?

Answer 2

A circuit in which the charge is split between branches.

Question 3

What two factors does the current in a circuit depend on?

Answer 3

1. Potential Difference (V)

2. Resistance (R)

Question 4

What equation should be used to calculate potential difference if current and resistance are known?

Answer 4

V = I R
Potential Difference (V), Current (A), Resistance (Ω)

Question 5

What is an ‘Ohmic Conductor’? State the condition

required

Answer 5

● A conductor for which current and potential difference are directly proportional.
● Resistance remains constant as current changes.
● Temperature must be constant.

Question 6

List four components for which resistance is not constant as current changes.

Answer 6

1. Lamps
2. Diodes
3. Thermistors
4. Light Dependant Resistors (LDRs)

Question 7

What happens to the resistance of a filament lamp

as the temperature increases? Why?

Answer 7

● Resistance increases.
● Ions in metal have more energy, so vibrate more, causing more collisions with electrons as they flow through the metal, creating greater resistance

Question 8

What is different about current flow through a diode?

Answer 8

● The current only flows in one direction.

● Resistance is very high in the other direction, preventing current flow.

Question 9

State what happens to the resistance of a thermistor as temperature increases.

Answer 9

The thermistor’s resistance decreases.

Question 10

Give two examples of when a thermistor may be used.

Answer 10

1. In a thermostat to turn a heater on below a certain temperature.
2. In a freezer to turn on a cooler when the temperature becomes too high.

Question 11

State what happens to the resistance of a LDR as

light intensity decreases.

Answer 11

The LDR’s resistance increases.

Question 12

Give an application for a LDR.

Answer 12

● Street lamps or night lights.

● When light levels become low enough, the light gains sufficient current to turn on.

Question 13

What are the two ways that a component can be

connected in a circuit?

Answer 13

1. Series (same loop)

2. Parallel (adjacent loop)

Question 14

How does the potential difference across two
components vary when connected in series and
parallel?

Answer 14

● Series: Total P.D is shared between each component.

● Parallel: P.D across each component is the same.

Question 15

If two resistors are connected in parallel, what can

be said about their combined total resistance?

Answer 15

Their total resistance is less than the smallest of the two individual resistances.

Question 16

If two resistors are connected in series, what can be

said about their total resistance?

Answer 16

Their total combined resistance is equal to the sum of the two individual resistances.

Question 17

State two equations for the power of a circuit. Give appropriate units.

Answer 17

P = I V           P = I² R
Power (Watts), Current (Amperes)
Potential Difference (Volts), Resistance (Ohms)

Question 18

State an equation linking energy transferred, power and time. Give appropriate units.

Answer 18

E= P t

Energy (Joules), Power (Watts), Time (Seconds)

Question 19

State an equation linking energy transferred, charge flow and potential difference. Give appropriate units

Answer 19

Energy (Joules), Charge (Coulombs), Potential Difference (Volts)

Question 20

How should an ammeter be connected in a circuit?

Answer 20

In series with the branch you are measuring the current for.

Question 21

How should a voltmeter be connected in a circuit?

Answer 21

In parallel to the component that you are measuring the potential difference for.