PhysicsCBSE Class 12 · Board exam 2026, set 55/1/1 · 2 marks · Very short answer

CBSE Class 12 Physics 2026: question 17

Set in the CBSE Class 12 board exam of 2026, paper 55/1/1, section B, question 17, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q17 · 2 marks · Very short answerDual Nature of Radiation and Matter

In a photoelectric experiment, the emitter plate is irradiated with radiation of 200 nm. The photocurrent becomes zero when the collector plate potential is $- 0.80$ V. Calculate the work function (in eV) of the emitter.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 55/1/1.

Hints

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

Hint 1

The collector potential at which the current becomes zero is the stopping potential.

Hint 2

Use $\frac{h c}{λ} = ϕ_{0} + e V_{0}$ , with $h c \approx 1240$ eV nm.

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.

Photon energy: $E = \frac{h c}{λ} = \frac{1240 eV nm}{200 nm} = 6.2 eV$
1 mark
The photocurrent stops at a collector potential of $- 0.80$ V, so the stopping potential is $V_{0} = 0.80$ V. Hence $K_{ma x} = e V_{0} = 0.80$ eV.
½ mark
Einstein's photoelectric equation gives $ϕ_{0} = \frac{h c}{λ} - e V_{0} = 6.2 - 0.80 = 5.4 eV$
½ mark

Answer: Work function ≈ 5.4 eV

Where the marks are

Calculates photon energy of about 6.2 eV (1 mark)
Identifies the stopping potential as 0.80 V and uses Einstein's equation (½ mark)
Obtains a work function of 5.4 eV (½ mark)

Revise the chapter

Chapter: Dual Nature of Radiation and Matter (notes, formulas, where marks are lost and every past question)

Practise this chapterBoard-style questions from Dual Nature of Radiation and Matter, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 55/1/1: every question, by section.

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CBSE Class 12 Physics 2026: question 17

Hints

Step-by-step solution

Revise the chapter

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