Confusing q


1. Key K is connected in turn to each of the contacts over short identical time intervals so that change in charge on capacitor is small. Final charge on cap is:

1)2.5 C
2)5 C
3)0.5 C

2. There is a dielectric rod b/w charges q1 and q2 and now the rod is removed. Net force on q1 now:

Increases
decreases
Remains same
Both 1 and 2 depending on nature of charges

4 Answers

62
Lokesh Verma ·

The first question is a very good question..

Think of a charge q there.. on the capacitor...

In the time dt, the charge on the capacitor will be given by

3=dq/dt+q/c

3dt = dq + qdt/c

In the next time dt, the charge dq should flow out.. so here, the dq should be -ve of the dq in the first loop.

2=dq/dt+q/c
2dt=dq+qdt/c

so,

3dt+2dt=2qdt/c

so q=5/2C

62
Lokesh Verma ·

If we ignore the end effect, the electric field outside the dielectric does not change due to the introduction of a dielectric..

So outside the dielectric, there is no change in the electric field..

So there will be no change in the force on the two rods.

62
Lokesh Verma ·

btw what is the source of the 1st question?

1
cipher1729 ·

thanks for the answers bhaiya..
both the qs are from the 'success magnet' question bank of Aaakash Institute.

First one is correct
But ans to q2 is given as d)

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