PhysicsCBSE Class 12 · Board exam 2023, set 55/1/1 · 3 marks · Short answer

CBSE Class 12 Physics 2023: question 30(a)

Set in the CBSE Class 12 board exam of 2023, paper 55/1/1, section C, question 30(a), for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q30(a) · 3 marks · Short answerAtoms

Draw the energy level diagram for hydrogen atom. Mark the transitions corresponding to the series lying in the ultraviolet region, visible region and infrared region.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 55/1/1.

Hints

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

Hint 1

Use $E_{n} = - 13.6/ n^{2}$ eV to label the levels.

Hint 2

Each series ends on a fixed lower level; the larger the energy gap, the shorter the wavelength.

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.

Energy level diagram (described): horizontal lines for $n = 1, 2, 3, 4, 5, \dots, \infty$ with energies $E_{n} = - 13.6/ n^{2}$ eV: $- 13.6$ eV ( $n = 1$ ), $- 3.4$ eV ( $n = 2$ ), $- 1.51$ eV ( $n = 3$ ), $- 0.85$ eV ( $n = 4$ ), $- 0.54$ eV ( $n = 5$ ), 0 eV ( $n = \infty$ ); levels crowd together as n increases.
1½ marks
Ultraviolet region: Lyman series — downward arrows from $n = 2, 3, 4, \dots$ to $n = 1$ .
½ mark
Visible region: Balmer series — downward arrows from $n = 3, 4, 5, \dots$ to $n = 2$ .
½ mark
Infrared region: Paschen series — arrows from $n = 4, 5, \dots$ to $n = 3$ (also Brackett to $n = 4$ and Pfund to $n = 5$ lie in infrared).
½ mark

Answer: UV: Lyman ( $\to n = 1$ ); Visible: Balmer ( $\to n = 2$ ); IR: Paschen ( $\to n = 3$ ), Brackett, Pfund.

Where the marks are

Energy level diagram with correct energies (1½ marks)
Lyman transitions marked as UV (½ mark)
Balmer transitions marked as visible (½ mark)
Paschen (or Brackett/Pfund) transitions marked as IR (½ mark)

Revise the chapter

Chapter: Atoms (notes, formulas, where marks are lost and every past question)

Practise this chapterBoard-style questions from Atoms, one at a time, marked against the answer key and marking points.Back to the full paper2023 board paper, set 55/1/1: every question, by section.

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CBSE Class 12 Physics 2023: question 30(a)

Hints

Step-by-step solution

Revise the chapter

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