Manipal Entrance Test 2017 Physics Paper

Let capacitance of each capacitor is C. Then equivalent capacitance in series is

1

C′

=

1

C

+

1

C

=

2

C

⇒C′=

C

2

Charge Q=C′V=

C

2

×15 ..(i)
When filled with dielectric
C1=4C,C2=C

1

C′

=

1

4C

+

1

C

=

5

4C

⇒C′=

4C

5

Since, charge is conserved
Q=C′V′=

4C

5

V′ ...(ii)
From Eqs. (i) and (ii), we get

C

2

×15=

4C

5

V′
⇒V′=

15×5

4×2

=9.4V=10V