T4.3.2 Circuits with heat, light, sound and movement Quiz: KS3 Design & Technology, Unit 4

The 20 questions

1. Which component converts electrical energy into heat in a kettle?

   • A microphone, which converts sound waves into an electrical signal for the circuit
   • A heating element, a coil of high-resistance wire that gets hot when current flows through it
   • A capacitor, which stores charge and releases it in a short pulse when required
   • A diode, which allows current to flow through it in one direction only

2. Why does an ordinary filament lamp give out a lot of heat as well as light?

   • The filament has a very low resistance, so it draws much less current than an LED
   • Most of the electrical energy it uses is transferred as heat rather than light
   • The filament converts all of its energy into sound, which makes the glass hot to touch
   • The filament is made of metal that absorbs light and then gives it out as heat

3. How does a piezo buzzer produce a sound?

   • A resistor increases in size as the current is turned up, pushing the air outwards
   • A crystal changes shape rapidly when a voltage is applied, making the surrounding air vibrate
   • A light sensor flashes on and off, producing a pattern of sound for the listener
   • A magnet heats up and then cools down, which makes the air around the buzzer move

4. Which component detects sound and converts it into an electrical signal?

   • A microphone
   • A loudspeaker, which converts electrical signals into sound waves in the air
   • A piezo buzzer, which produces a fixed tone when a voltage is applied to it
   • A DC motor, which turns a shaft when a current is supplied through its coil

5. What does a solenoid do in a circuit?

   • It stores electrical charge between two metal plates separated by an insulator
   • It uses a coil to create a magnetic field that pulls a metal plunger in or out
   • It changes its resistance when the temperature of the air around it changes
   • It emits light when current flows through it in the forward direction only

6. What does a tilt switch detect?

   • Whether the switch has been stretched by an applied force, which changes its resistance
   • Whether light falls onto a cell, which then changes its resistance to match the brightness
   • Whether a magnetic field is brought close to it, which closes the contacts inside
   • Whether the device is tilted, using a small metal ball that closes the contacts when it rolls

7. A product should sound an alarm when a door is opened. Which combination of components is most suitable?

   • A reed or magnetic switch as the input and a buzzer as the output
   • An LDR as the input and a heater element as the output, with a battery supplying power
   • A microphone as the input and a capacitor as the output, with a switch to control it
   • A thermistor as the input and a lamp as the output, with a resistor to limit the current

8. A heater must switch off when the water reaches a set temperature. Which input is needed?

   • An LDR placed in the water, whose resistance changes with the brightness of the light
   • A microphone placed in the water, which detects the sound of the boiling water
   • A tilt switch placed in the water, which closes when the water is moved about
   • A thermistor placed in the water, whose resistance changes with temperature

9. A light sensor controls a garden lamp that switches on at dusk. Which resistor behaviour is needed?

   • The sensor's resistance falls in the dark, so the lamp switches off at dusk instead
   • The sensor's resistance rises only when a sound is heard close to the lamp at night
   • The sensor's resistance rises in the dark, so the transistor switches the lamp on
   • The sensor's resistance stays fixed whatever the light level, so the lamp stays on

10. A buzzer draws too much current from a microcontroller pin. What is the best fix?

    • Connect the buzzer straight to the 5 V pin with no component in between
    • Replace the buzzer with a longer length of wire to reduce the current drawn
    • Add more lamps in parallel with the buzzer so that the current is shared out
    • Drive the buzzer through a transistor, so that a small current switches a larger current

11. How can the direction of a DC motor be reversed?

    • Connect a larger resistor in series with the motor to change its direction of spin
    • Place a magnet next to the motor casing so that its rotation is stopped completely
    • Swap the connections to the motor so the current flows through it in the opposite direction
    • Increase the voltage to the motor so that it spins faster in the same direction

12. A heating element has a resistance of 12 ohms and is connected to a 12 V supply. What is its power output?

    • 144 W
    • 1 W
    • 24 W
    • 12 W

13. Which change would make a heating circuit produce more heat from the same supply voltage?

    • Using a shorter piece of the same heating wire, which lowers its resistance
    • Using a longer piece of the same heating wire, which increases its resistance
    • Connecting a resistor in series with the heating element to limit the current
    • Replacing the supply with a battery of lower voltage to keep the element cooler

14. What is the effect of a piezo buzzer's switching rate on the sound it makes?

    • The rate sets only the loudness, while the pitch stays fixed at the same level always
    • The rate sets the colour of the buzzer's casing so that it can be seen in the dark
    • The rate sets the frequency of the vibration, which determines the pitch of the note
    • The rate sets the length of the battery, so the buzzer runs for a longer time

15. Which conversion takes place inside a loudspeaker?

    • Heat is changed into movement by a strip that bends when it is warmed by the sun
    • An electrical signal drives a coil that moves a cone to push air and make sound
    • Sound is changed into an electrical signal by a magnet moving across a fixed coil
    • Light is changed into sound by a crystal that changes shape when it is illuminated

16. A light sensor is covered by a hand. What happens to its resistance and the current in the circuit?

    • Its resistance falls, so the current in the circuit rises sharply
    • Its resistance stays the same, because a hand cannot affect the light reaching it
    • Its resistance drops to zero, so the circuit has no current flowing through it at all
    • Its resistance rises, so the current in the circuit falls

17. A product gives a flashing light and a sound when a button is pressed. Which output devices are needed?

    • An LED for the flashing light and a buzzer for the sound
    • A resistor for the flashing light and a capacitor for the sound
    • A solenoid for the flashing light and an LDR for the sound
    • A microphone for the flashing light and a thermistor for the sound

18. Which statement about a heating element at a constant supply voltage is correct?

    • Its power output rises when its resistance falls
    • Its power output falls when its resistance falls, because less current flows
    • Its power output depends only on the frequency of the supply and not on resistance
    • Its power output is unaffected by its resistance at any supply voltage

19. Which output device turns most of its electrical energy directly into light?

    • An LED, which converts most of its electrical energy directly into light
    • A filament lamp, which is heated until it glows and wastes much energy as heat
    • A heating element, which converts almost all of its electrical energy into heat
    • A buzzer, which converts most of its electrical energy into sound rather than light

20. Why does a DC motor run more slowly when its supply voltage is reduced?

    • A lower voltage makes the shaft heavier, so it cannot turn at its normal full speed
    • A lower voltage makes the magnet inside the motor stronger, so the shaft turns more slowly
    • A lower voltage drives less current through the motor, which gives less turning effort and a slower speed
    • A lower voltage raises the resistance of the motor coil, which makes the shaft slow down

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