Answer
Given,
Periscope uses 45-45-90 prisms with total internal reflection adjacent to 45°.
refractive index of water, n_a = 1.33
refractive index of glass, n_g = 1.52
When the light enters the water, water will act as a lens and when we see the object from the periscope the object shown is farther than the usual distance.
Explanation :
Magnetic field, B = 5.2 T
Electric field, 
The directions of the two fields are perpendicular to each other. Hence the force due to each field will equate each other.
Electrostatic force, F =qE.........(1)
Magnetic force, F = qvB........(2)
From equation (1) and (2)
E = v B




Hence, the correct option is (a).
(2) A permanent magnet always has two poles as the North pole and south pole. The magnetic field lines start from north poles and terminate at the south pole of the magnet.
Hence, the correct option is (C).
The 50 W bulb would have a greater current than the 90 W bulb
Answer:

Explanation:
The question says that, "The closest star to the earth is 2 light years away. Calculate this distance in SI units".
Given that,
The distance between the closest star and the Earth is 2 light years.
The SI unit of distance is m. It means we need to convert light years to meters. We know that,

2 light-years means,

So, the required distance is equal to
.
As per the question the total distance is given as 4 km.
We are asked to calculate the average speed.
The time taken by the body to travel each kilometre are 5.9 min,6.2 min.,6.3min. and 6 min. respectively.
The average speed of a body is defined as the ratio of total distance travelled by the body to the total time.
Mathematically the average speed is written as _
V= Total distance/Total time
i.e V = S/T
Where S is the total distance travelled and T is the total time
Here total distance (S)= 4 km
The total time T= (5.9+6.2 +6.3+ 6.0 )minutes
=24.4 min.
Hence average speed V = 4 km/24.4 min
= 0.16 km/min.
Hence the correct option is A .