15 km 30 divided by 4 is 7.5 km in 30 min times that by 2 the answer is 15
Answer:
(a). The angle of refraction is 19.26°.
(b). That is proved that the rays in air on either side of the glass are parallel to each other
Explanation:
Given that,
Angle of incidence = 30.0°
Index of reflection of glass = 1.52
(a). We need to calculate the angle of refraction for the ray inside the glass
Using snell's law


Put the value into the formula



(b). We know that,
The incident ray and emerging ray is equal then the ray will be parallel.
We need to prove that the rays in air on either side of the glass are parallel to each other
Using formula for emerging ray


Put the value into the formula



So, 
This is proved.
Hence, (a). The angle of refraction is 19.26°.
(b). That is proved that the rays in air on either side of the glass are parallel to each other
Battery based heaters use electric resistance heating, which uses a lot of current (electricity) to create the heat.
There is no apparatus for it. It is either use something like ruler and table and rub together or rub our hands, and friction force will be showed.