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Answer the following. (Science 2023 31/4/1 Q36)

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ScienceCBSE Class 10 · Board exam 2023, set 31/4/1 · 5 marks · Long answer

CBSE Class 10 Science 2023: question 36

Set in the CBSE Class 10 board exam of 2023, paper 31/4/1, section D, question 36, for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q36 · 5 marks · Long answerElectricity

Answer the following.

  1. (i)

    How is electric current related to the potential difference across the terminals of a conductor ? Draw a labelled circuit diagram to verify this relationship.

    2 marks
  2. (ii)

    Why should an ammeter have low resistance ?

    1 mark
  3. (iii)

    Two V - I graphs A and B for series and parallel combinations of two resistors are as shown. Giving reason state which graph shows (a) series, (b) parallel combination of the resistors.

    2 marks

Figure in the paper: V-I graph with I on the vertical axis and V on the horizontal axis, both axes starting from origin. Two straight lines through the origin: line B is steeper (higher slope, i.e. larger I for the same V), and line A is less steep, lying below B. See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 31/4/1.

Hints

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

Hint 1

Recall the law that links V, I and R.

Hint 2

Think about how the ammeter is placed in the circuit and what extra resistance would do to the current.

Hint 3

With I on the y-axis, the slope of the graph equals 1/R. Which combination has more resistance?

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) Ohm's law: at constant temperature, the current through a conductor is directly proportional to the potential difference across its ends. So , i.e. .

    1 mark

  2. (i) Circuit diagram (described): a battery, a plug key, an ammeter (A) and a resistor R (nichrome wire XY) are all connected in series. A voltmeter (V) is connected in parallel across the resistor. The +/– terminals of the ammeter and voltmeter are marked, and arrows show the direction of current. Varying the number of cells changes V, and each time V and I are noted; V/I comes out constant.

    1 mark

  3. (ii) An ammeter is connected in series, so the whole current passes through it. If it has low resistance, it does not add to the total resistance of the circuit and does not change the current it is measuring.

    1 mark

  4. (iii) In the I–V graph, slope . So a smaller slope means a larger resistance.

  5. (a) Graph A shows the series combination: it has the smaller slope, so its resistance is larger. Series resistance is the greater value.

    1 mark

  6. (b) Graph B shows the parallel combination: it has the larger slope, so its resistance is smaller. Parallel resistance is less than the smallest individual resistance.

    1 mark

Answer: (i) I ∝ V (Ohm's law), verified with the ammeter in series and the voltmeter across the resistor; (ii) so that it does not change the current in the circuit; (iii) (a) series – A (less slope, more R); (b) parallel – B (more slope, less R)

Where the marks are

  • States that I is directly proportional to V / Ohm's law (1 mark)
  • Draws a labelled circuit with ammeter in series and voltmeter in parallel, with current direction (1 mark)
  • Gives the reason for low ammeter resistance: series connection, so it must not alter the current (1 mark)
  • Identifies graph A as series with reason (less slope, more resistance) (1 mark)
  • Identifies graph B as parallel with reason (more slope, less resistance) (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 paper2023 board paper, set 31/4/1: 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.