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 in the same.

Question 2

What is a parallel circuit?

Answer 2

A circuit in which the charges is split between branches.

Question 3

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

Answer 3

• Potential Difference (V)

- Resistance (Ω)

Question 4

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

Answer 4

V (V) = I (A) R (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

• Lamps
• Diodes
• Thermistors
• LDRs

Question 7

What happens to the resistance of a filament lamp as 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 temperatute increases.

Answer 9

The thermistor’s resistance decreases

Question 10

Give two examples of why a thermistor may be used.

Answer 10

• Thermostat

- Freezer

Question 11

What happens to the resistance of an LDR when Light intensity decreases?

Answer 11

The LDR’s resistance increases

Question 12

Give an application for a LDR

Answer 12

• Street Lamps

- Night Lights

Question 13

What are the two ways that a component can be connected in a circuit?

Answer 13

• Series

- Parallel

Question 14

How does PD across two components vary when connected in series and parallel?

Answer 14

• Series: Total PD is shared between each component

- Parallel: PD across each component is the same

Question 15

If two resistors are connected in parallel, what can be said about their total resistance?

Answer 15

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

Question 16

If two resistors are connected in parallel, what can be said about their combined total resistance?

Answer 16

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

Question 17

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

Answer 17

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

Power (W) = Current^2 (A) x Resistance (Ω)

Question 18

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

Answer 18

Energy (J) = Power (W) x Time (s)

Question 19

How should a Voltmeter be connected in a circuit?

Answer 19

In parallel to the desired component

Question 20

how should an ammeter be connected in a circuit?

Answer 20

In series in the direction of current flow