A) 3,000
B) 9,000
C) 18,000
D) 36,000
Correct Answer: C
Solution :
Given: Velocity of light \[c=3\times {{10}^{8}}\,m/s\] \[2\theta =48\pi \times {{10}^{-3}}\,\text{rad}\] \[\Rightarrow \] \[\theta =24\pi \times {{10}^{-3}}\,\text{rad}\] Distance of rotating mirror from concave mirror d = 6000 m Velocity of light in air is, \[c=\frac{4\pi nd}{\theta }\] or \[n=\frac{c\theta }{4\pi d}\] Putting, given values in above expression \[n=\frac{3\times {{10}^{8}}\times 24\pi \times {{10}^{-3}}}{4\pi \times 6000}=300\,\]turn/s For one minute number of turn will be = 300 x 60 = 18000 turns/min
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