The laser in an audio compact disc uses light of wavelength $7.8 \times 10^2 \mathrm{~nm}$. What is the…

The laser in an audio compact disc uses light of wavelength $7.8 \times 10^2 \mathrm{~nm}$. What is the frequency of light emitted by laser?
  1. $1.8 \times 10^{14} \mathrm{~s}^{-1}$
  2. $2.6 \times 10^{14} \mathrm{~s}^{-1}$
  3. $5.4 \times 10^{14} \mathrm{~s}^{-1}$
  4. $3.8 \times 10^{14} \mathrm{~s}^{-1}$

Solution

$\lambda=7.8 \times 10^2 \mathrm{~nm}=7.8 \times 10^2 \times 10^{-9} \mathrm{~m}$ $\begin{aligned} & =7.8 \times 10^{-7} \mathrm{~m} \\ & \Rightarrow \quad \mathrm{v}=\frac{\mathrm{c}}{\lambda}=\frac{3 \times 10^8 \mathrm{~ms}^{-1}}{7.8 \times 10^{-7} \mathrm{~m}}=3.8 \times 10^{14} \mathrm{~s}^{-1}\end{aligned}$

Asked in: AP EAMCET 2023 (16 May Shift 2)

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