CBSE Class 12 Physics 2024: question 20

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Step-by-step solution

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1. (a) The photon energy equals the energy gap: $E_2-E_1=\frac{hc}{\lambda }$.

   $E_2-E_1=2.55\times 1.6\times 10^{-19}$ J.

   ½ mark

2. $\lambda =\frac{6.63\times 10^{-34}\times 3\times 10^8}{2.55\times 1.6\times 10^{-19}}=4.875\times 10^{-7}\text{m}=487.5\text{nm}$

   1 mark

3. (b) 487.5 nm lies in the visible region. It corresponds to the transition $n=4\to n=2$, since $-0.85-(-3.40)=2.55$ eV.

   So the line belongs to the Balmer series.

   ½ mark

Answer: (a) λ ≈ 487.5 nm; (b) Balmer series

Revise the chapter

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