15 A laser beam takes 24 ms to travel from a rocket to the reflective surface of

Question

15 A laser beam takes 24 ms to travel from a rocket to the reflective surface of a planet and back to the rocket. How far is the rocket from this planet's surface? (c 3.0 x 108 m/s A) 2400 km B) 1200 km C) 1800 km D) 3600 km E) 4800 km 16) At a particular point and instant, the magnetic field component of an electromagnetic wave is 15.0 HT. What is the magnetic energy density of this wave at that point and instant? (c 3.00 x 108 m/s, Ho x 107 T.m/A, go 8.85 x A) 2.26 x 10-4 J/m3 B) 8.95 x 10-5 J/m3 C) 1.79 x 10-4 J/m3 D) 4.47 x 10-4 J/m3 E) 9.72 x 10-5 J/m3

Explanation / Answer

15) D)3600 km

let d is the distance between rocket and planet

Apply time taken, t = 2*d/c

d = t*c/2

= 24*10^-3*3*10^8/2

= 3.6*10^6 m

= 3600 km

16) B) 8.95 J/m^3

we know, magnetic energy desnity, u_B = B^2/(2*mue)

= (15*10^-6)^2/(2*4*pi*10^-7)

= 8.95*10^-5 J/m^3

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