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Plot a graph showing the… (Class 12 Physics 2024, Q21)

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PhysicsCBSE Class 12 · Board exam 2024, set 55/1/1 · 2 marks · Very short answer

CBSE Class 12 Physics 2024: question 21

Set in the CBSE Class 12 board exam of 2024, paper 55/1/1, section B, question 21, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q21 · 2 marks · Very short answerSemiconductor Electronics: Materials, Devices and Simple Circuits

Plot a graph showing the variation of current with voltage for the material GaAs. On the graph, mark the region where :
(a) resistance is negative, and
(b) Ohm's law is obeyed.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 55/1/1.

Hints

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

Hint 1

GaAs is the NCERT example of a non-ohmic material whose I–V graph is not monotonic.

Hint 2

Resistance is negative where current decreases even though voltage increases.

Hint 3

Ohm's law holds only where the graph is a straight line through the origin.

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. Graph (described): Current I is on the y-axis and voltage V on the x-axis. Starting from the origin, I rises linearly with V up to a peak. Beyond the peak, I decreases as V increases, falling to a minimum. After the minimum, I rises again with V.

    1 mark

  2. (a) The portion between the peak and the minimum, where I decreases while V increases (), is marked as the negative resistance region.

    ½ mark

  3. (b) The initial straight-line portion through the origin, where , is marked as the region where Ohm's law is obeyed.

    ½ mark

Answer: Graph rises linearly, falls after a peak, then rises again. Falling part = negative resistance; initial linear part = Ohm's law obeyed.

Where the marks are

  • Correct shape of the I–V graph for GaAs (1 mark)
  • Marks the falling part as the negative resistance region (½ mark)
  • Marks the initial linear part as the region where Ohm's law holds (½ mark)

Revise the chapter

Practise this chapterBoard-style questions from Semiconductor Electronics: Materials, Devices and Simple Circuits, one at a time, marked against the answer key and marking points.Back to the full paper2024 board paper, set 55/1/1: 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.