Physics Quiz: P6- Electrical Circuits
Time allowed: 60 minutes Total marks: 50
Section A: Multiple Choice Questions (MCQ) [10 marks]
-
An ammeter is used to measure which electrical quantity? [1]
A) Potential difference (p.d.)
B) Current
C) Resistance
D) Power -
What is the correct circuit position for a fuse in relation to the live wire? [1]
A) In parallel with the live wire
B) In series before the appliance, on the live wire
C) In series after the appliance, on the neutral wire
D) Connected directly to earth -
If an LDR (Light Dependent Resistor) is placed in a potential divider circuit: how does its resistance change when light intensity increases? [1]
A) Increases significantly
B) Remains constant
C) Decreases significantly
D) Becomes infinite -
Which of the following circuits would remain operational if one lamp filament blows? [1]
A) Series circuit only
B) Parallel circuit only
C) Both series and parallel
D) Neither -
What is the formula for combined resistance in a parallel circuit (for two resistors)? [1]
A) $R_\text{total} = R1 + R2$
B) $\frac{1}{R_\text{total}} = \frac{R1 \times R2}{R1 + R2}$
C) $\frac{1}{R_\text{total}}= \frac{1}{R1} + \frac{1}{R2}$
D) $R_\text{total} = \frac{R1 + R2}{2}$ -
Which appliance should have the highest fuse rating? [1]
A) Lamp bulb (3 A)
B) Microwave oven (13 A)
C) Kettle (5 A)
D) Phone charger (1 A) -
In a potential divider circuit, what happens to $V_\text{out}$ if R1 is increased? [1]
A) $V_\text{out}$ increases
B) $V_\text{out}$ decreases
C) $V_\text{out}$ stays the same
D) $V_\text{out}$ becomes zero -
Why must electrical switches be connected in series with the live wire? [1]
A) To allow current to flow faster
B) To isolate the appliance from high voltage when turned off
C) To protect the neutral wire from damage
D) Both B and C -
What is the function of a circuit breaker compared to a fuse? [1]
A) Circuit breakers are always higher quality than fuses
B) Circuit breakers can be reset after tripping, unlike fuses which must be replaced
C) They work differently - they don’t trip
D) Both A and B -
When cells are connected in series helping each other, how is the total e.m.f. calculated? [1]
A) $E_\text{total} = E1 \times E2 \times …$
B) $E_\text{total} = E1 + E2 + …$
C) $E_\text{total} = \frac{E1 + E2}{2}$
D) $E_\text{total} = E1 - E2 + …$
Section B: Short Answer Questions
- Circuit Components and Symbols [6 marks]
a) Complete the table below by explaining the function of each component in a circuit. [4 marks]
| Component | Function | Mark |
|---|---|---|
| Resistor (Fixed) | [1 mark] | |
| Diode | [1 mark] | |
| Thermistor (NTC) | [1 mark] | |
| Transformer | [1 mark] |
b) Why must a voltmeter be connected in parallel rather than series with a component being measured? [2 marks]
- Series and Parallel Circuits [8 marks]
a) Three 1.5 V cells are connected in series helping each other. One resistor of 4 Ω is connected to the circuit. Calculate:
- Total e.m.f. of the supply [1 mark]
- Current flowing through the resistor (assume ideal wires) [3 marks]
- Why does this configuration give more current than just a single cell? [2 marks]
b) Two 6 Ω resistors are connected in parallel across a 12 V power supply. Calculate:
- Combined resistance of the two resistors [2 marks]
- Current through each resistor [2 marks]
- Potential Dividers and Sensors [8 marks]
a) A potential divider circuit is built using two resistors in series. The input voltage ($V_\text{in}$) is 9 V. R1 = 3 kΩ, R2 = 6 kΩ. Calculate the output voltage $V_\text{out}$ across R1. [3 marks]
b) Explain how the voltage reading on an analogue voltmeter connected to the potential divider output will behave when:
- The circuit uses an LDR and ambient light increases [2 marks]
- The circuit uses an NTC thermistor and temperature decreases [2 marks]
c) Why are variable potential dividers (potentiometers) useful in electronic devices as volume controls? [1 mark]
- Electrical Safety and Protection [8 marks]
a) List FOUR hazards associated with mains electricity that can lead to fires or electric shock. [4 marks]
b) Describe how a fuse protects an electrical appliance from fire hazard when the live wire touches the metal casing of a three-pin plug. [3 marks]
c) Why is double insulation preferred over earthing for appliances like hair dryers? [1 mark]
Section C: Extended / Essay Questions
-
Comprehensive Circuit Analysis [10 marks]
-
A potential divider uses an NTC thermistor ($R_\text{thermistor}$) and a 3 kΩ fixed resistor connected to a 9 V supply. The thermistor is placed at the bottom of the divider (connected to earth).
- Draw and label this circuit diagram [1 mark]
- When the thermistor temperature increases from 20°C to 50°C, its resistance falls from 6 kΩ to 1 kΩ. Calculate $V_\text{out}$ at each temperature [3 marks]
- Explain why this circuit is suitable for a frost alarm system [2 marks]
-
Describe the construction and operation of an LDR as used in a twilight switch that operates street lights automatically when it gets dark. Explain the potential divider configuration required to trigger a relay when $V_\text{out}$ exceeds 8 V [3 marks]
-
-
Series and Parallel Applications [10 marks]
-
Consider a domestic lighting circuit wired in parallel with 4 lamps, each rated at 120 Ω, operated at 230 V mains supply. Three of the lamps are working normally while one bulb’s filament blows.
- Calculate total resistance BEFORE the lamp fuses [1 mark]
- Calculate total current drawn from the supply [2 marks]
- Explain using circuit theory why the remaining lamps continue to glow AFTER the filament blows [3 marks]
-
Now consider these four same lamps re-wired in SERIES and operated at 230 V mains.
- Calculate combined resistance [1 mark]
- Calculate current through each lamp [2 marks]
- Explain why this would be unsuitable for standard lighting applications compared to the parallel arrangement [4 marks]
-
Attempt the quiz before checking the mark scheme
Mark Scheme P6 - Electrical Circuits Mark Scheme
Topic guide: P6 - Electrical Circuits