No Longer On Exam

Question 1

What is electric current?

Answer 1

The flow of electrical charge/electrons.

Question 2

State the equation linking charge, current and time. Give the units for the quantities involved

Answer 2

Q = I t

Charge (coulombs), current (amps), time (seconds).

Question 3

What can be said about the value of current at any point in a single closed loop?

Answer 3

Current is the same at all points in a closed loop.

Question 4

What 2 factors does the current in a circuit depend on?

Answer 4

• Potential difference (V).

- Resistance (R).

Question 5

What equation should be used to calculate potential difference if current and resistance are known? State the units for all 3 quantities

Answer 5

V = I R
Potential difference (V), current (A), resistance (Ω).

Question 6

What is an ‘ohmic conductor’. State the conditions required

Answer 6

• An ohmic conductor for which current and potential difference are directly proportional.
• Resistance remains constant as current changes.
• Temperature must be constant.

Question 7

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

Answer 7

• Bulbs/lamps.
• Diodes.
• Thermistors.
• Light dependent resistors.

Question 8

What happens to the resistance of a filament lamp as temperature increases? Why?

Answer 8

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

Question 9

What is different about current flow through a diode?

Answer 9

• The current only flows in one direction.

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

Question 10

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

Answer 10

The thermistor’s resistance decreases.

Question 11

Give 2 examples of when a thermistor may be used

Answer 11

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

Question 12

State what happens to the resistance of a LDR as light intensity decreases

Answer 12

The LDR’s resistance increases.

Question 13

Give an application for a LDR

Answer 13

• Street lights often use LDRs.

- When light levels become too low, the light gains sufficient current to turn on.