CUET · PHYSICS · PYQ PAPER 2025
Light with an energy flux of \( 18 \text{ W/cm}^2 \) falls at normal incidence on a non-reflecting surface of area \( 20 \text{ cm}^2 \). If the light falls for 30 minutes on the surface, find the total momentum delivered to the surface.
- A \(10^{-3} Kg m s ^{-1}\)
- B \(2.16 Kg m s ^{-1}\)
- C \(4.32 \times 10^{-3} Kg m s ^{-1}\)
- D \(2.16 \times 10^{-3} Kg m s ^{-1}\)
Answer & Solution
Correct Answer
(D) \(2.16 \times 10^{-3} Kg m s ^{-1}\)
Step-by-step Solution
Detailed explanation
\( U = IAt \) \( U = (18 \text{ W/cm}^2)(20 \text{ cm}^2)(30 \times 60 \text{ s}) = 648000 \text{ J} \) \( \Delta p = \frac{U}{c} \) \( \Delta p = \frac{648000 \text{ J}}{3 \times 10^8 \text{ m/s}} = 2.16 \times 10^{-3} \text{ Kg m s}^{-1} \)
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