National 5PhysicsSQAExam QuestionsElectricityPractical Electrical & Electronic Circuits

Practical Electrical & Electronic Circuits (SQA National 5 Physics): Exam Questions

Exam code: X857 75

39 mins16 questions
11 mark

A circuit containing an LDR switches on a motor when the light level drops below a certain value.

The resistance of the LDR increases as the light level decreases.

Which of the following shows this circuit?

  • Circuit diagram with an LDR and variable resistor in series, connected to a transistor controlling a motor, powered by +Vs and 0V.
  • Circuit diagram showing a motor connected to a transistor, with a photodiode and a variable resistor between positive supply and ground.
  • Electronic circuit diagram showing a motor, variable resistor, fixed resistor, and a voltage source with connections to positive and ground terminals.
  • Circuit diagram showing a motor connected to a transistor, with variable resistors labelled 't' and connected to +Vs and 0V terminals.
  • Electronic circuit diagram with variable resistors, transistor, and motor connected to a power source labelled +Vs and 0V at the bottom.

Choose your answer

2a
Sme Calculator4 marks

A student sets up the following circuit.

Circuit diagram with a 12V battery, switch S1, two 36Ω parallel resistors, switch S2 in series, a 24Ω resistor, and an ammeter.

Initially, both switch S1 and switch S2 are open

The student closes switch S1.

Determine the reading on the ammeter.

How did you do?

2b
Sme Calculator6 marks

The student now also closes switch S2.

(i) Determine the total resistance of this circuit.

[4]

(ii) State whether the reading on the ammeter will now be less than, equal to or greater than the value determined in (a).

You must justify your answer.

[2]

How did you do?

3a4 marks

A capacitor consisting of two parallel metal plates, X and Y, is connected in a circuit as shown.

Circuit diagram with a battery, switch, plates X and Y separated by distance d, and a coulomb meter connected in parallel.

The distance d between plate X and plate Y can be adjusted.

The capacitor is initially uncharged.

The switch is moved to position A and charge is transferred to the capacitor.

The switch is now moved to position B and the charge Q stored on the capacitor is measured by the coulombmeter.

This process is repeated for a range of different distances d between plate X and plate Y.

The charge Q stored on the capacitor for a range of different distances d between plate X and plate Y is shown in the table.

d (mm)

Q (×10−12 C)

10

178

20

90

30

62

40

47

50

37

(i) Using the graph paper, draw a graph of these results.

[3]

Graph paper with a dense grid of small squares, marked with bold lines every five squares. Edged with numbered axes for plotting data.

(ii) Use your graph to determine the charge stored on the capacitor when the distance between plate X and plate Y is 25 mm.

[1]

How did you do?

3b2 marks

Suggest two ways in which the experimental procedure could be improved.

How did you do?

41 mark

A circuit is set up as shown.

A circuit diagram with a 12V battery, two resistors, two ammeters labelled A1 and A2, and a voltmeter. Ammeter A1 is after the battery.

The resistors are identical.

Which row in the table shows the reading on the voltmeter and possible readings on ammeters A1 and A2?

Reading on voltmeter (V)

Reading on ammeter A1​ (A)

Reading on ammeter A2​ (A)

A

6

0.3

0.3

B

6

0.6

0.3

C

12

0.3

0.3

D

12

0.3

0.6

E

12

0.6

0.3

    Choose your answer

    51 mark

    Which of the following symbols represents a thermistor?

    • Outline drawing of a speaker icon, featuring a simple shape with two lines indicating sound waves, set against a plain white background.
    • Symbol for a variable resistor with a diagonal line through a rectangle, indicating adjustability, used in electrical circuit diagrams.
    • Electrical circuit symbol for a lamp or light bulb, featuring a circle with a cross inside, connected by straight lines on either side.
    • Horizontal rectangle with thin lines extending from each side, resembling a resistor symbol often used in electronic circuit diagrams.
    • Symbol of a mechanical fluid damper with a rectangular shape, two diagonal arrows indicate direction, and lines extend horizontally on either side.

    Choose your answer

    6
    Sme Calculator    5 marks

    Two resistors are connected in a circuit as shown.

    Circuit diagram with a 6V battery, an ammeter, and two parallel resistors labelled 4Ω and 16Ω.

    (i) Calculate the total resistance of the circuit.

    [3]

    (ii) Another ceramic power resistor is now connected in parallel with the two resistors in the circuit.

    State the effect this change has on the reading on the ammeter.

    Justify your answer.

    [2]

    How did you do?

    74 marks

    A dehumidifier is an appliance that extracts water from the air around it.

    Illustration of a portable air conditioning unit with control buttons on top, air vents on the front and side, and small wheels on the bottom.

    One particular dehumidifier operates at 230 V a.c. and has a power rating of 0.35 kW.

    The dehumidifier switches on automatically when the moisture in the air increases above a certain level. This causes an LED to light and a fan to turn on.

    Part of the circuit diagram for the circuit is shown.

    Circuit diagram featuring a moisture sensor and variable resistor connected to control a fan circuit, with labeled points X and Y for electrical reference.

    (i) Complete the circuit diagram to show the LED connected correctly between X and Y.

    [1]

    (ii) The voltage across the moisture sensor decreases as the moisture in the air increases.

    Explain how the circuit operates to turn on the LED when the moisture in the air increases above a certain level.

    [2]

    (iii) Explain the purpose of the variable resistor in this circuit.

    [1]

    How did you do?

    81 mark

    A student sets up the circuits shown.

    In which circuit will both LEDs be lit?

    • Electrical circuit diagram with a battery, two resistors, an LED, and a diode in series. Arrows indicate LED light emission direction.
    • Electrical circuit diagram with battery, two light-emitting diodes (LEDs), and a resistor connected in series, illustrating current flow through the components.
    • Simple electrical circuit diagram featuring two diodes, a power source, and a resistor, arranged in a rectangular layout with directional arrows.
    • Electrical circuit diagram featuring a battery, two LEDs, and a resistor connected in series, forming a closed loop with current flow direction indicated.
    • Simple electric circuit diagram showing a battery, two LEDs facing opposite directions, and a resistor connected in a loop.

    Choose your answer

    91 mark

    A circuit is set up as shown.

    Circuit diagram with a 6V battery, variable resistor marked R, fixed resistor, LDR, and a bulb in a series-parallel configuration.

    The room temperature is 20 °C.

    The lamp is off.

    The lamp will light when

    • the light level is decreased below a certain value

    • the light level is increased above a certain value

    • the resistance of R is increased above a certain value

    • the battery voltage is reduced to 5 V

    • the temperature is increased above a certain value

    Choose your answer

    101 mark

    A circuit is set up as shown.

    Electrical circuit diagram with three resistors, R1, R2, and R3, two voltage sources, V1 and V2, and one battery, Vs, connected in a network.

    A student makes the following statements about the readings on the voltmeters.

    I V subscript 1 equals V subscript 2

    II V subscript 2 equals V subscript 3

    III V subscript S equals V subscript 1 plus V subscript 2

    Which of these statements must always be true?

    • II only

    • I and II only

    • I and III only

    • II and III only

    • I, II and III

    Choose your answer

    11
    Sme Calculator    1 mark

    A circuit is set up as shown.

    Circuit diagram showing a battery, two resistors (16Ω and 24Ω) in parallel with voltmeters V1 and V2 measuring voltage across each resistor.

    The reading on voltmeter V1 is 3.6 V.

    The reading on voltmeter V2 is

    • 0.4 V

    • 2.2 V

    • 2.4 V

    • 3.6 V

    • 5.4 V

    Choose your answer

    121 mark

    A circuit is set up as shown.

    Electrical circuit diagram with a battery, three resistors, three ammeters labelled A1, A2, A3, and an adjustable resistor with directional arrows.

    The resistance of the LDR increases as the light level decreases.

    The light level incident on the LDR decreases.

    Which row in the table describes the effect of this change on the readings on the ammeters?

    Reading on ammeter A1​

    Reading on ammeter A2​

    Reading on ammeter A3​

    A

    decreases

    decreases

    decreases

    B

    decreases

    stays the same

    stays the same

    C

    stays the same

    stays the same

    stays the same

    D

    increases

    stays the same

    stays the same

    E

    increases

    increases

    increases

      Choose your answer

      13
      Sme Calculator      1 mark

      Three resistors are connected as shown.

      Parallel circuit diagram with three resistors: 12 ohms at the top, 6 ohms in the middle, and 4 ohms at the bottom, connected between points X and Y.

      The total resistance between X and Y is

      • 0.5 Ω

      • 2.0 Ω

      • 4.0 Ω

      • 6.0 Ω

      • 22 Ω

      Choose your answer

      143 marks

      A wireless charger uses radio waves to charge the battery of a mobile phone.

      Diagram showing a mobile phone on a wireless charger stand with a power flex. Labels indicate parts: mobile phone, wireless charger, and flex.

      The charger is connected to a direct current (d.c.) supply via a flex.

      During use the charger heats up.

      The charger contains a fan that switches on automatically when the temperature of the charger increases above a certain level.

      Part of the circuit containing the fan is shown.

      Circuit diagram showing a transistor, a fan motor labelled 'M', a switch, and two resistors connected to a 5V power supply.

      As the temperature of the charger increases, the resistance of the thermistor decreases.

      Explain how the circuit operates to switch on the fan when the temperature of the charger increases above a certain level.

      How did you do?

      151 mark

      A transistor switching circuit is set up as shown.

      Electronic circuit diagram featuring a potentiometer, resistors, an NPN transistor, and an LED, connected between a positive voltage supply and ground.

      The variable resistor is adjusted until the LED switches off.

      The temperature of the thermistor is now increased.

      The resistance of the thermistor decreases as the temperature increases.

      Which row in the table describes the effect of this change on the voltage across the thermistor, the voltage across the variable resistor, and whether the LED stays off or switches on?

      Voltage across the thermistor

      Voltage across the variable resistor

      LED

      A

      decreases

      increases

      switches on

      B

      decreases

      decreases

      switches on

      C

      decreases

      decreases

      stays off

      D

      increases

      decreases

      stays off

      E

      increases

      increases

      switches on

        Choose your answer

        16
        Sme Calculator        1 mark

        Three resistors are connected as shown.

        Circuit diagram with three 12-ohm resistors. One is in series with points X and Y, and the other two are in parallel between them.

        The resistance between X and Y is

        • 4 Ω

        • 6 Ω

        • 18 Ω

        • 24 Ω

        • 36 Ω

        Choose your answer