A simple pendulum is having bob of mass m carrying a charge q and is hanging from ceiling. A uniform electric field E is applied in downward direction then time period of simple pendulum is.

### Asked by ruchiaggarwal083 | 12th May, 2021, 08:47: AM

Expert Answer:

### Period of simple pendulam in absence of electric field is given as
where l is length of simple pendulam and g is acceleration due to gravity.
When the electric field is present , in addition to gravitational force ,
we have force (qE ) due to electric field in the same direction of gravitational force.
Hence downward acceleration due to this electric field is force / mass = [ ( qE ) / m ]
where q is the charge on the bob of pendulam , E is electric field intensity and m is mass of pendulam

Hence change in period T of simple pendulam is given as
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Second question
Force F between two charges of equal magnitude q is given as
.................................(1)
Since force F is directly proportional to square of charge magniude,
charge magnitude has to be made as 2q to get force 4F .
Hence increase in charge = q
From eqn.(1), we get q as

..........................(2)
if e is charge on electron, number of electrons n is to be added is determined as
Hence we get ,

### Answered by Thiyagarajan K | 12th May, 2021, 02:19: PM

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