In the 25 ft Space Simulator facility at NASA\'s Jet Propulsion Laboratory, a ba

Question

In the 25 ft Space Simulator facility at NASA's Jet Propulsion Laboratory, a bank of overhead arc lamps can produce light of intensity 2500 W/m2 at the floor of the facility. (This simulates the intensity of sunlight near the planet Venus.) Assume that the actual intensity is 2330 W/m2 for this problem (a) Find the average radiation pressure (in pascals and in atmospheres) on a totally absorbing section of the floor. Pa atm (b) Repeat for a totally reflecting section of the floor. Pa atm (c) Find the average momentum density (momentum per unit volume) in the light at the floor. kg/m2

Explanation / Answer

a)

For totally absorbing surface

P = I/c

P = 2330 W/m^2 / (3 x 10^8 m/s)

P = 7.7667 x 10^-6 Pa

1 atm = 1.01 x 10^5 pa

p =  7.7667 x 10^-6 Pa / 1.01 x 10^5 pa

p = 7.69 x 10^-11 atm

b)

for totally reflecting surface :

P = 2I/c

P = 2 x  7.7667 x 10^-6 Pa

P = 15.5334 x 10^-6 Pa

P = 15.5334 x 10^-6 Pa / 1.01 x 10^5 pa

P = 15.3796 x 10^-11 atm

c)

momentum density = I/c^2

= 2330 / (3 x 10^8)^2

= 2.5889 x 10^-14 kg.m^2 .s

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