Option (b) is correct.The index of refraction for the glass is 1.52
Explanation:
velocity of light in vacuum= C= 2.99 x 10⁸m/s
Velocity of light in glass = V= 1.97 x 10⁸m/s
The refractive index is given by n=
n= 2.99 x 10⁸/1.97 x 10⁸m/s
n= 1.52
Thus the refractive index of glass is 1.52
Answer:
the required electrical power when the room air and surroundings are at 30°C.= 52.51822 Watt
Explanation:
Power required to maintain the surface temperature at 150°C from 20°C
P= εσA(T^4-t^4)
P= power in watt
ε= emissivity
A= area of surface
T= 150°C= 423 K
t= 20°C= 303K
/sigma= 5.67×10^{-8} watt/m^2K^4
putting vales we get

P=52.51822 Watt
the required electrical power when the room air and surroundings are at 30°C.= 52.51822 Watt
40% the formula is work output/work input*100 so
200/500=.4*100=40