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Answer the following. (Science 2024 31/5/1 Q36a)

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ScienceCBSE Class 10 · Board exam 2024, set 31/5/1 · 5 marks · Long answer

CBSE Class 10 Science 2024: question 36(a)

Set in the CBSE Class 10 board exam of 2024, paper 31/5/1, section D, question 36(a), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q36(a) · 5 marks · Long answerElectricity

Answer the following.

  1. (i)

    The potential difference across the two ends of a circuit component is decreased to one-third of its initial value, while its resistance remains constant. What change will be observed in the current flowing through it? Name and state the law which helps us to answer this question.

    2 marks
  2. (ii)

    Draw a schematic diagram of a circuit consisting of a battery of four 1·5 V cells, a 5 resistor, a 10 resistor and a 15 resistor and a plug key, all connected in series. Now find (I) the electric current passing through the circuit, and (II) potential difference across the 10 resistor when the plug key is closed.

    3 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 31/5/1.

Hints

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

Hint 1

Which law links V, I and R? What happens to I if V changes while R stays fixed?

Hint 2

In series, the cell voltages add up and the resistances add up.

Hint 3

Use I = V/R for the whole circuit, then V = IR for the 10 Ω resistor alone, since the current is the same everywhere in series.

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) By Ohm's law, . With constant and , we get . So the current becomes one-third of its initial value.

    ½ mark

  2. The law used is Ohm's law.

    ½ mark

  3. Statement: The potential difference across the ends of a conductor is directly proportional to the current flowing through it, provided its temperature (and other physical conditions) remain the same. That is, , or .

    1 mark

  4. (ii) Circuit diagram (in words): Draw four cell symbols joined positive to negative to form a battery of . Connect it in one single loop with a plug key and the resistors , and , one after the other in series. Mark the direction of current from the + terminal round the loop.

    1 mark

  5. (I) Total voltage: .

    Series resistance: .

    Current: .

    1 mark

  6. (II) The same current flows through every resistor in series. So the p.d. across the resistor is .

    1 mark

Answer: (i) Current becomes one-third; Ohm's law (V ∝ I at constant temperature). (ii) (I) 0.2 A; (II) 2 V

Where the marks are

  • States that the current becomes one-third of its initial value (½ mark)
  • Names Ohm's law (½ mark)
  • States Ohm's law correctly, including the constant-temperature condition (1 mark)
  • Draws a correct series circuit with four cells, three resistors and a plug key (1 mark)
  • Finds total V = 6 V and R = 30 Ω, then I = 0.2 A (1 mark)
  • Finds p.d. across the 10 Ω resistor = 2 V (1 mark)

Revise the chapter

  • Chapter: Electricity (notes, formulas, where marks are lost and every past question)
  • Topic: Ohm's Law
Practise this chapterBoard-style questions from Electricity, one at a time, marked against the answer key and marking points.Back to the full paper2024 board paper, set 31/5/1: 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.