T4.3.1 Powering advanced electrical systems Quiz: KS3 Design & Technology, Unit 4

The 20 questions

1. Which electrical component stores energy chemically and supplies a steady direct current?

   • A resistor, which limits the flow of current through a circuit path
   • A capacitor, which can only store energy for a very short moment
   • A transformer, which changes the voltage of alternating current in the mains
   • A battery, made from one or more electrochemical cells

2. What is the effect of connecting two identical 1.5 V cells in series?

   • The total voltage stays 1.5 V, but the current capacity doubles
   • The total voltage becomes 0.75 V, because the cells share the load
   • The total voltage becomes 3 V, and the cells last only half as long
   • The total voltage becomes 3 V, while the current capacity stays the same

3. In a parallel circuit with two identical lamps, what happens to the voltage across each lamp?

   • Each lamp has twice the voltage of the supply, because the lamps are added
   • Each lamp has half the voltage of the supply, shared between the two lamps
   • Each lamp has zero voltage, because one of the lamps blocks the other
   • Each lamp has the same voltage as the supply

4. Which is the best description of a light-dependent resistor, or LDR?

   • A component that resists changes in temperature by storing charge in its plates
   • A component whose resistance rises when the light falling on it becomes brighter
   • A component that emits light when a current flows through it in one direction
   • A component whose resistance falls when the light falling on it becomes brighter

5. What does a light-emitting diode, or LED, do in a circuit?

   • It lets current flow in one direction only and emits light when it conducts
   • It converts light falling on it into a steady direct current for the supply
   • It stops current flowing in either direction once the voltage has reached three volts
   • It stores charge and releases it slowly to keep the circuit lit after the power is off

6. What is a thermistor used for in a circuit?

   • Producing sound, because it vibrates when a current is passed through its structure
   • Storing charge for a short time, so that the circuit keeps working during a power cut
   • Sensing temperature, because its resistance changes as its temperature changes
   • Switching the circuit on automatically when the surrounding light level is high enough

7. What is an output device in an electrical circuit?

   • A component that stores charge so that the circuit can keep running for a while
   • A component that senses a change in the environment and sends a signal into the circuit
   • A component that limits the current so that the circuit is protected from damage
   • A component that converts electrical energy into another form, such as light, sound or movement

8. Using Ohm's law, what is the current through a 300 ohm resistor connected across a 9 V supply?

   • 2700 A, which would overheat the resistor very quickly
   • 0.03 A, or 30 mA
   • 33.3 A, which is too large for a resistor of this size
   • 0.3 A, or 300 mA

9. A circuit has two identical resistors in series. What is the total resistance if each one is 100 ohms?

   • 200 ohms
   • 10000 ohms
   • 50 ohms
   • 100 ohms

10. Two identical resistors are connected in parallel. What is the total resistance if each is 100 ohms?

    • 100 ohms, because parallel branches do not change the resistance
    • 50 ohms, because the current has two paths to take
    • 200 ohms, because the resistances add together in any circuit
    • 10 ohms, because the resistance is divided by ten in every parallel branch

11. A circuit uses a transistor as a switch. What does a small current at the base allow?

    • A reduction in the current between the collector and the emitter to zero
    • A larger current to flow between the collector and the emitter, switching a device on
    • A change of the transistor into a battery that gives out a steady current
    • A large voltage to be stored in the base, so that the switch can stay on for hours

12. Which energy form does a motor convert electrical energy into?

    • Chemical energy, which is stored in the motor's coil until it is needed later
    • Light energy, which is given off when the motor's coil reaches a high temperature
    • Sound energy, which is made by the motor's casing vibrating against the case
    • Kinetic energy, which is the energy of movement

13. A designer wants a circuit that turns a fan on when a room gets hot. Which pair of components would be best?

    • An LDR as the input and a buzzer as the output, with a capacitor storing the charge
    • A thermistor as the input and a motor as the output, with a transistor switching the motor
    • A microphone as the input and a lamp as the output, with a battery supplying the power
    • A switch as the input and an LED as the output, with a resistor limiting the current

14. What is a buzzer used for in a circuit?

    • Storing charge so that the circuit keeps running after the power is cut off
    • Measuring the temperature of the water around the circuit so the user can see it
    • Producing a sound when current flows through it
    • Lighting up a room when the switch is pressed by the user of the product

15. Which component is used as a variable resistor to control a volume setting?

    • A potentiometer, which has a wiper that changes the resistance when it is turned
    • A relay, which switches a separate circuit on or off using an electromagnet
    • A thermistor, which changes its resistance only when the temperature of the air rises
    • A capacitor, which stores charge and releases it in a single short pulse

16. What is a relay used for?

    • Converting alternating current from the mains into direct current for a battery
    • Reducing the voltage of the supply so that a lamp is protected from damage
    • Switching a high-current circuit on or off using a separate low-current control circuit
    • Storing energy for a short time so that the circuit keeps working during a brief outage

17. Why are fuses fitted in the electrical circuits of many products?

    • To change direct current into alternating current so that the motor runs more smoothly
    • To break the circuit if the current becomes too high, protecting components and wiring
    • To store energy so that the product still works during a brief power cut from the mains
    • To increase the voltage of the supply to the motor so that it runs faster

18. Three lamps are connected in parallel. If one lamp breaks, what happens to the other two?

    • They stay lit, because each lamp has its own path back to the supply
    • The other two lamps become brighter, because the current is shared between them
    • All three lamps go out, because the circuit is now incomplete and cannot work
    • The other two lamps go out, because the voltage across them drops to zero volts

19. Which component is used to store electrical charge?

    • A capacitor
    • A thermistor, which changes its resistance with the temperature around it
    • A resistor, which limits the current flowing through a circuit
    • A diode, which allows current to flow through it in one direction only

20. Why is a resistor placed in series with an LED?

    • To store energy so that the LED stays lit when the battery is disconnected
    • To change the direction of current so that the LED lights up on both half cycles
    • To increase the current so that the LED shines much more brightly and clearly
    • To limit the current through the LED so that it is not damaged by too much current

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