The speed of light in a material is given by:

where

is the speed of light in vacuum
n is the refractive index of the material
The lens in this problem has a refractive index of n=1.50, therefore the speed of light in the lens is

And the correct answer is C).
Answer:
The magnitude of force is 1.86 N and the direction of force is towards the other wire.
Explanation:
Given:
Current flowing through each power line, I = 130 A
Distance between the two power lines, d = 40 cm = 0.4 m
Length of power lines, L = 220 m
The force exerted by the power lines on each other is given by the relation:

Substitute the suitable values in the above equation.

F = 1.86 N
Since the direction of current flowing through the power lines are opposite to each other, so the force is attractive in nature. Hence, the direction of force experienced by the power lines on each other is towards the each other.
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The answer is Strontium(Sr)