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  • Light with an energy flux of 20 wb cm2 falls on a non-reflecting surface at normal incidence If the surface has an area of 30 cm2 the total momentum delivered for 30 minutes is

Light with an energy flux of 20 wb/cm2 falls on a non-reflecting surface at normal incidence. If the surface has an area of 30 cm2, the total momentum delivered for 30 minutes is

A.    108 × 104 kg m/s

B.    36 × 10-5 kg m/s

C.    1.08 × 107 kg m/s

C.    36 × 10-4 kg m/s

Answers (1)

Answer: The answer is the option (d) 36 \times 10^{-4} kg m/s

Solution: \phi = energy\; flux = 20 \;wb/ cm^{2}

\\A = Surface \;area = 30 cm^{2}\\\\t = time = 30 \times 60 seconds = 1800 seconds

U = Energy falls on the surface in that time = \phi At = 20 \times 30 \times 1800 J = 1080000 J

Momentum of the incident light = \frac{U}{c} = 1080000/3 \times 10^{8} = 36 \times 10^{-4} kg m/s

As the momentum of the reflected light is zero, then momentum of the delivered light is 36 \times 10^{-4} kg \;m/s

Posted by

infoexpert21

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