Resistance in Series and Parallel · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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One path or many paths

Science · Energy · ages 14-16
Name ______________________   Date ____________

  1. In series, the same current flows through every resistor.

    Circle one:   True   False

  2. Two 10 ohm resistors sit in series. What is the total?

    • 20 ohms
    • 10 ohms
    • 5 ohms

  3. Two fixed 12 ohm resistors are rewired from series into parallel. Which change in total resistance is correct?

    • From 24 ohms to 48 ohms
    • From 24 ohms to 24 ohms
    • From 24 ohms to 6 ohms

  4. A working lamp is added in parallel across a supply that keeps the same voltage. After temperatures settle, what happens to supply current?

    • It falls because each lamp gets half the voltage
    • It rises because both branches now draw current
    • It stays unchanged because the supply sets current

  5. Fixed resistors of 4 ohms, 6 ohms and 10 ohms are in series across a 10 V supply. Ignore wire resistance. What is the current in amperes? Type the number.

    Answer: ______________

  6. You want to measure the current through a resistor in a supervised low-voltage circuit. Where should the ammeter be connected?

    • In parallel across the resistor
    • In series with the resistor
    • In parallel across the supply terminals

  7. Two lamps form the only parallel branches across a 6 V supply. Lamp P draws 0.20 A; lamp Q draws 0.30 A. Sam calculates 0.30 - 0.20 = 0.10 A for supply current. Which correction fits?

    • 0.20 A, counting only the current through lamp P
    • 0.50 A, adding both measured branch currents
    • 0.30 A, counting only the current through lamp Q

  8. A bulb in a series string fails and breaks the only current path. There is no bypass around it. What happens to the bulbs?

    • The remaining bulbs brighten; current bypasses the gap
    • The remaining bulbs stay on; only voltage is shared
    • All bulbs go out; the only current path is broken
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Answer key

For grown-ups. Fold this page away before handing over the rest.

One path or many paths W1-mt_B29m3h5B75-s1

  1. True · One path means one current everywhere in it.
  2. 20 ohms · Add the series resistances: 10 plus 10 is 20.
  3. From 24 ohms to 6 ohms · In series, 12 + 12 = 24 ohms. Two identical parallel resistors have half one resistor's resistance: 12 / 2 = 6 ohms.
  4. It rises because both branches now draw current · The original lamp still has the same voltage. The added lamp draws extra current, which adds to the current already drawn.
  5. 0.5 · Total resistance is 4 + 6 + 10 = 20 ohms. Current = supply voltage / total resistance = 10 / 20 = 0.5 A.
  6. In series with the resistor · Connect the ammeter in series so the resistor's current passes through it. An ammeter across the supply can cause a short circuit.
  7. 0.50 A, adding both measured branch currents · Supply current includes both branch currents: 0.20 + 0.30 = 0.50 A. Subtraction gives the difference between them, not their total.
  8. All bulbs go out; the only current path is broken · The broken path makes an open circuit. With no bypass, current stops through every bulb in the string.
Worksheet · LightMySky