Answer:

Explanation:
Energy density in magnetic field is given as;

where;
B is the magnetic field strength
Energy density of electric field

where;
E is electric field strength
Take the ratio of the two fields energy density


But, Electric field potential, V = E x L = IR (I is current and R is resistance)

Now replace E x L with IR

Also, B = μ₀I / 2πr, substitute this value in the above equation

cancel out the current "I" and factor out μ₀

Finally, the equation becomes;

Therefore, the correct option is (d) μ₀/ϵ₀ (L /R 2πr)²
The period of the orbit would increase as well
Explanation:
We can answer this question by applying Kepler's third law, which states that:
"The square of the orbital period of a planet around the Sun is proportional to the cube of the semi-major axis of its orbit"
Mathematically,

Where
T is the orbital period
a is the semi-major axis of the orbit
In this problem, the question asks what happens if the distance of the Earth from the Sun increases. Increasing this distance means increasing the semi-major axis of the orbit,
: but as we saw from the previous equation, the orbital period of the Earth is proportional to
, therefore as
increases, T increases as well.
Therefore, the period of the orbit would increase.
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The electrostatic force between the two ions is 
Explanation:
The electrostatic force between two charged particle is given by Coulomb's law:

where
is the Coulomb's constant
are the two charges
r is the separation between the two charges
In this problem, the ion of sodium has a charge of

while the ion of chlorine has a charge of

And the distance between the two ions is

Substituting, we find the electrostatic force between the two ions:

where the negative sign simply means that the force is attractive, since the two ions have opposite charge.
Learn more about electrostatic force:
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Explanation:
Given that,
Mass of the block, m = 12.2 kg
Initial velocity of the block, u = 6.65 m/s
The coefficient of kinetic friction, 
(a)The force of kinetic friction is given by :

mg is the normal force
So,

(b) Net force acting on the block in the horizontal direction,
f = ma
a is the acceleration of the block

(c) Let d is the distance covered by the block before coming to the rest. Using third equation of motion as follows :

Hence, this is the required solution.
Compression and rarefraction, the other guy's answer it's wrong