Q.
Light with energy flux of 18 W/cm2 falls on a non reflecting surface of area 20 cm2 at normal incidence. The momentum delivered in 30 minutes is
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a
1.2 × 10–6 kgms–1
b
2.16 × 10–3 kgms–1
c
1.8 × 10–3 kgms–1
d
3.2 × 10–3 kgms–1
answer is B.
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Detailed Solution
Energy flux = 18 Wcm–2 = 18 x104 Wm-2Total energy incidentU = flux x Area x time = 18 x104 x 20 x 10-4 x 30 x 60 = 18 x 36 x 103Momentum deliveredP=UC=18 x 36 x 1033 x 108=2.16 x 10-3 kg ms-1
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