Answer:

Explanation:
Given:
- wavelength of light in the air,

- time taken to travel from the source to the photocell via air,

- time taken to reach the photocell via air and glass slab,

- thickness of the glass slab,

<u>Now we have the relation for time:</u>

hence,

c= speed of light in air



For the case when glass slab is inserted between the path of light:
(since light travel with the speed c only in the air)
here:
v = speed of light in the glass


Using Snell's law:



Answer:
the si unit of electric current is Ampere .the flow of charge in a close circuit is called electric current
Answer:
Option (D)
Explanation:
Terrestrial planets refers to those four planets that are nearest to the sun and that lies within the asteroid belt. These planets are mainly composed of rocks or other metal objects that have a hard and resistant surface on it. They have a metal core that is molten (liquid) in nature, and atmosphere is relatively less dense, and also various geological features are present on it like the crater, volcanoes which can be observed with the help of satellites. The average densities of these planets is about four times the density of water. For example, the density of water is 1 g/cm³, whereas the density of earth is 5.5 g/cm³.
Thus, the correct answer is option (D).
Answer:
39.240 W
Explanation:
Let's start by calculating the work done by the engine. We can assume that it is the same work done by the weight of the object to bring it from 40m to the surface: as much energy it takes to bring it up, the same ammount it takes to bring it down. Said work is 
At this point we can simply apply the definition of power, that is
, to get the power of the engine is 