Question

the ratio of electric potential at points 10cm and20cm from the centre of an electric dipole along its axis line is​

Answer 1

Explanation:

magnetic intensity on the axis of a magnet from its centre at a distance r

B=

4π(r

2

−L

2

)

2

μ

0

2rM

The ratio of magnetic intensity on the axis at a distance r

1

and r

2

is B

1

and B

2

⇒

B

2

B

1

=

1

12.5

⇒r

1

=10cm,r

2

=20cm

⇒

B

2

B

1

=

4π(r

2

2

−L

2

)

2

μ

0

2r

2

M

4π(r

1

2

−L

2

)

2

μ

0

2r

1

M

=

r

2

(r

1

2

−L

2

)

2

r

1

(r

2

2

−L

2

)

2

⇒

1

12.5

=

20(10

2

−L

2

)

2

10(20

2

−L

2

)

2

⇒

1

5

=

10

2

−L

2

20

2

−L

2

⇒500−5L

2

=400−L

2

⇒4L

2

=100

⇒L=5cm

Length of the magnet is 2L

⇒2L=2×5cm=10cm

Hence correct option is C.