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Science 9

Science 9 · Worksheets

Electrical principles and technologies

Ten questions of mixed difficulty, covering Electricity. Print it, or work through it on screen — the answer key starts on its own page.

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Electrical principles and technologies

Science 9 · maddyhelps.com

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Circle the best answer for each question. Show your work in the space provided.

  1. To measure the voltage across a lamp, a voltmeter must be connected

    1. a) in series, next to the lamp
    2. b) between the switch and the lamp
    3. c) in parallel, across the lamp
    4. d) in series with the battery

  2. In a dry cell, such as an AA battery, the electrolyte is

    1. a) a solid metal
    2. b) distilled water
    3. c) a liquid acid
    4. d) a moist paste

  3. Two bulbs are connected in series to a battery. An ammeter placed before the first bulb reads 0.4 A. An ammeter placed after the second bulb will read

    1. a) 0.8 A
    2. b) 0.4 A
    3. c) 0 A
    4. d) 0.2 A

  4. In a natural gas power plant, the order of energy changes from the fuel to the power line is

    1. a) thermal → chemical → mechanical → electrical
    2. b) chemical → electrical → mechanical → thermal
    3. c) chemical → thermal → mechanical → electrical
    4. d) chemical → mechanical → thermal → electrical

  5. A remote northern community makes its electricity with diesel generators and is deciding whether to add a solar farm. Which fact most strongly supports building it?

    1. a) It would cut the diesel that must be trucked or flown in
    2. b) Diesel generators have powered the town reliably for many years
    3. c) Solar panels make electricity only in daylight
    4. d) Solar panels are a newer kind of technology

  6. A generator at a hydroelectric dam converts

    1. a) mechanical energy into electrical energy
    2. b) electrical energy into thermal energy
    3. c) chemical energy into electrical energy
    4. d) electrical energy into mechanical energy

  7. Kettle A uses 200 kJ of electrical energy to put 150 kJ of thermal energy into the water. Kettle B uses 180 kJ to put 144 kJ into the water. Which is more efficient?

    1. a) Kettle A, because it delivers more energy
    2. b) Kettle B, at 80%
    3. c) Kettle A, at 75%
    4. d) They are equal, as both waste some energy

  8. A hair dryer draws 10 A from a 120 V outlet. Its power is

    1. a) 1200 W
    2. b) 12 W
    3. c) 130 W
    4. d) 0.083 W

  9. A student's model generator, a coil turned by hand between two magnets, lights a small bulb only dimly. Which change would most likely make the bulb brighter?

    1. a) Turning the coil more slowly
    2. b) Using weaker magnets
    3. c) Using fewer turns of wire
    4. d) Turning the coil faster

  10. A 1.5 kW space heater runs 4 h a day for 30 days. Electricity costs 15¢ per kWh. What does it cost to run for the month?

    1. a) $2700.00
    2. b) $0.90
    3. c) $27.00
    4. d) $180.00

Answer key · Electrical principles and technologies

Science 9 · maddyhelps.com

  1. c) in parallel, across the lamp — A voltmeter compares the energy carried by the charge on either side of the lamp, so its two leads go on either side of it, in parallel. It is the ammeter that goes in series, because it has to count the current flowing through.
  2. d) a moist paste — A dry cell is not really dry: its electrolyte is a paste, so it cannot spill. A wet cell, such as a traditional car battery, uses a liquid electrolyte, which is where the liquid acid answer comes from.
  3. b) 0.4 A — Current is the flow of charge, and in a series circuit the same charge passes through every part, so the current is the same everywhere. The bulbs take energy from the charge, not the charge itself: current is not used up.
  4. c) chemical → thermal → mechanical → electrical — Burning the gas releases its chemical energy as heat, the heat drives a spinning turbine, and the turbine turns a generator. Every step wastes some energy as heat, which is why the plant as a whole is less efficient than any one of its steps.
  5. a) It would cut the diesel that must be trucked or flown in — Less fuel to buy and haul is a real saving in cost and pollution, so it is evidence for the solar farm. Daylight-only output is true but argues against it, and being newer is not a benefit by itself.
  6. a) mechanical energy into electrical energy — Falling water spins a turbine, which turns the generator, where magnets and coils of wire move past each other to produce electricity. A motor does the reverse, turning electrical energy into motion.
  7. b) Kettle B, at 80% — Efficiency is useful output ÷ input × 100%: A is 150 ÷ 200 = 75% and B is 144 ÷ 180 = 80%. Kettle A delivers more energy only because it uses more; what matters is how much of each joule ends up in the water.
  8. a) 1200 W — P = IV = 10 × 120 = 1200 W, or 1.2 kW. Dividing instead gives 12 W, far too little to heat air; checking that the answer is sensible for a heating appliance catches the slip.
  9. d) Turning the coil faster — A generator makes current by moving wire through a magnetic field, and the faster the motion, the greater the voltage. More turns of wire and stronger magnets also help; fewer turns and weaker magnets do the opposite.
  10. c) $27.00 — Energy = power × time = 1.5 kW × 120 h = 180 kWh, and 180 × $0.15 = $27.00. $180 comes from stopping at the kilowatt-hours, and $2700 from treating 15 cents as 15 dollars.