Question

A force of 4N is acting between two charges in air. If the space between them
is completely filled with glass (ε= 8), then the new force will be
1) 2N
2) 5N
3) 0.2N
4) 0.5N
​

Answer 1

Given :

Force between the charges when they kept in air = 4N

∈$_{r}$ = 8

To Find :

The force when space between the charges if filled with glass

Solution :

Force (F) = $\frac{1}{4\pi E_{o} } \frac{Qq}{r^{2} }$  = 4N  (when the medium is air)

Force when space between the charges is filled with glass (F') = $\frac{1}{4\pi E_{o}E_{r} } \frac{Qq}{r^{2} }$

                                                                                                   F'  = $\frac{F}{E_{r} }$

                                                                                                   F'  = $\frac{4}{8}$

                                                                                                   F'  = $\frac{1}{2}$ = 0.5N

∴ Force when space between the charges is filled with glass (F') is 0.5N.

Option (4) is correct.

         

Answer 2

Answer:

0.5N

Explanation:

We know,

The force between two charged object in air (F) = $\frac{1}{4\pi ∈}$ $\frac{q_1{q_{2} } }{d^{2} }$

A/Q, 4N is acting between 2 objects in air

Therefore,

                 $\frac{1}{4\pi ∈}$$\frac{q_{1}q_{2} }{d^{2} }$ = 4

Now,

    We have to find the force when charges are in glass. it is given the

    (∈= 8),

    Formula when the objects are kept in other medium F' = $\frac{1}{4\pi ∈∈'}$$\frac{q_{1}q_{2} }{d^{2} }$

      => F' = $\frac{F}{∈'}$   [ Since, F = $\frac{1}{4\pi ∈}$$\frac{q_{1}q_{3} }{d^{2} }$ ]

      => $\frac{4}{8}$

      => 0.5N

Hence, The the new force is 0.5N

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