The refractive index is used to measure how much light bends as it goes from one medium to another the refractive index of air =1 as light doesn’t bend in it
When looking into a glass of water with a straw the straw may appear bent or morphed as the water has a different refractive index to air (and the light is passing from air to glass of water)
The efficiency of the device is 30 %
Explanation:
The efficiency of a heat engine is given by:

where
W is the work done by the engine
is the heat in input to the engine
For the device in this problem, we have:
W = 120 J is the work done
is the heat in input
Substituting, we find the efficiency:

which corresponds to an efficiency of 30%.
Learn more about work:
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<span>On the surface of the Earth, the escape velocity is about 11.2 km/s, which is approximately 33 times the speed of sound (Mach 33) and several times the muzzle velocity of a rifle bullet (up to 1.7 km/s). However, at 9,000 km altitude in "space", it is slightly less than 7.1 km/s.</span>
These two electric and magnetic forces can be related together into one electromagnetic force through the Lorentz force law. This law states that the total force acting on a charged particle due to electric and magnetic fields is equal to the sum of the electric and magnetic forces acting on it.