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In an electric circuit three… (Class 10 Science 2023, Q36b)

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ScienceCBSE Class 10 · Board exam 2023, set 31/6/1 · 5 marks · Long answer

CBSE Class 10 Science 2023: question 36(b)

Set in the CBSE Class 10 board exam of 2023, paper 31/6/1, section D, question 36(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q36(b) · 5 marks · Long answerCompetency-basedElectricity

In an electric circuit three bulbs of 100 W each are connected in series to a source. In another circuit set of three bulbs of the same wattage are connected in parallel to the same source.
(i) Will the bulb in the two circuits glow with the same brightness? Justify your answer.
(ii) Now, let one bulb in both the circuits get fused. Will the rest of the bulbs continue to glow in each circuit? Give reason for your answer.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 31/6/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Think about how voltage is shared across bulbs in series compared with parallel.

Hint 2

Brightness depends on the power consumed, . Compare the voltage across one bulb in each circuit.

Hint 3

When a bulb fuses, ask whether there is still a complete path for current through the other bulbs.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. (i) No, the bulbs in the two circuits will not glow with the same brightness.

    1 mark

  2. Series circuit: The total resistance becomes , so the current falls. The source voltage is also shared, each bulb getting only . Each bulb therefore consumes less power, becomes , and the bulbs glow dimly.

    1 mark

  3. Parallel circuit: Each bulb gets the full source voltage and hence its required current. Each bulb works at its rated 100 W and glows with normal (full) brightness. So the bulbs in parallel glow brighter than those in series.

    1 mark

  4. (ii) Series circuit: If one bulb fuses, the only path for the current is broken. The circuit becomes open, no current flows, and none of the remaining bulbs glows.

    1 mark

  5. Parallel circuit: Each bulb is on a separate branch across the source. If one bulb fuses, the other two still get the full voltage and their own current. They continue to glow with the same brightness as before.

    1 mark

Answer: (i) No – the series bulbs glow dimly (voltage shared, current reduced) and the parallel bulbs glow at full brightness (full voltage across each). (ii) Series: no bulb glows (circuit broken); parallel: the other two glow with the same brightness.

Where the marks are

  • States No (1 mark)
  • Series: increased resistance, reduced current and shared voltage, so less power and dim glow (1 mark)
  • Parallel: each bulb gets full voltage and normal current, so normal brightness (1 mark)
  • Series: one bulb fused breaks the circuit, so no bulb glows (1 mark)
  • Parallel: the remaining bulbs glow with the same brightness as they still get the same voltage (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Electricity, one at a time, marked against the answer key and marking points.Back to the full paper2023 board paper, set 31/6/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.