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Explain- I. It is… (Class 12 Physics SQP 2026-27, Q23)

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PhysicsCBSE Class 12 · Sample paper, session 2026-27 · 3 marks · Short answer

CBSE Class 12 Physics sample paper 2026-27: question 23

From the official CBSE sample question paper for 2026-27, section C, question 23, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q23 · 3 marks · Short answerCompetency-basedCurrent Electricity

Explain-

I. It is easier to start a car engine on a warm day than on a chilly day.
II. The resistance of our body is so large, even then one experiences a strong shock (sometimes even fatal)) when one accidentally touches the live wire of, say 240 V supply.
III. Heat is generated continuously in an electric heater but its temperature becomes constant after some time.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2026-27.

Hints

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

Hint 1

For I, think about what limits the current a battery can deliver and how it depends on temperature.

Hint 2

For II, compute roughly V/R and think how little current the heart can tolerate.

Hint 3

For III, compare rate of heat produced with rate of heat lost to the surroundings.

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. The internal resistance of the car battery (electrolyte) decreases as temperature rises. On a warm day it is lower, so the battery can deliver the large current needed by the starter motor more easily.

    1 mark

  2. II. Even though body resistance is large, at 240 V can give a current of several milliamperes or more, and the human body (heart and nerves) is extremely sensitive to such small currents, so the shock is strong or even fatal.

    1 mark

  3. III. As the heater gets hotter than its surroundings, it loses heat at a rate that increases with temperature. When the rate of heat loss equals the rate of heat production (), a steady state is reached and the temperature stays constant.

    1 mark

Answer: I. Battery's internal resistance falls with temperature; II. body is sensitive to even a few mA; III. heat produced = heat lost at steady state.

Where the marks are

  • Internal resistance decreases on warm day → larger current (1 mark)
  • Body sensitive to currents of a few mA (1 mark)
  • Steady state when rate of heat produced equals rate of heat lost (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Current Electricity, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2026-27: 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.