Two bodies A and B radiate maximum energy with wavelength difference $4 \mu \mathrm{m}$. The absolute…

Two bodies A and B radiate maximum energy with wavelength difference $4 \mu \mathrm{m}$. The absolute temperature of body $\mathrm{A}$ is 3 times that of $\mathrm{B}$. The wavelength at which body B radiates maximum energy is:
  1. $2 \mu m$
  2. $4 \mu m$
  3. $6 \mu m$
  4. $12 \mu m$

Solution

Concept: According to the Wiens displacement law: $\lambda_m T=\text { Constant, }$ Given $\left(\lambda_{m B}-\lambda_{m A}\right)=4 \mu \mathrm{m} \quad---(1)$ $T_A=3 T_B \quad---(2)$ Now, using Wiens displacement law $T_A=\lambda_{m B} T_B \quad---(3)$ $\mathrm{Eq}^{\mathrm{n}}$ (2) divided by $\mathrm{Eq}^{\mathrm{n}}$ (3) $\begin{aligned} & \frac{1}{\lambda_{m A}}=\frac{3}{\lambda_{m B}} \\ & \Rightarrow \frac{\lambda_{m B}}{\lambda_{m A}}=3 \\ & \Rightarrow \frac{\left(\lambda_{m B}-\lambda_{m A}\right)}{\lambda_{m A}}=2 \\ & \Rightarrow \lambda_{m A}=\frac{1}{2}\left(\lambda_{m B}-\lambda_{m A}\right) \end{aligned}$ Now, using eq ${ }^{\mathrm{n}} 1$ $\begin{aligned} & \lambda_{m A}=\frac{1}{2}(4 \mu \mathrm{m})=2 \mu \mathrm{m} \\ & \therefore \lambda_{m B}=4 \mu+\lambda_{m A}=6 \mu \mathrm{m} \end{aligned}$

Asked in: MHT CET 2022 (08 Aug Shift 2)

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