Question

An electric lamp and a screen which are 1m apart are pluced on the table fin a line at what distance form the screen should 4 convex lens of trocal length 21cm be kept in order to get 9 sharp imuge clf the lemp?​

Answer 1

Explanation:

The following steps are to be taken to solve the query:

1) Using the distances in the diagram above we get u=−x and v=d−x.

2) Now, apply the lens formula and find the relation between the distances.

f1= x1+ d−x1

You will get a quadratic relation between x,

f and d as x

2 - xd + fd = 0 -------(1)

3) Substitute the value of d=100 cm

and f=21 cm to find the value of x.

so when we put f=21 and d=100

finally

Substituting these values in equation 1,

we get x

1 =70 cm and x 2

=30 cm

Answer 2

Explanation:

following steps are to be taken to solve the query:

1) Using the distances in the diagram above we get u=−x and v=d−x.

2) Now, apply the lens formula and find the relation between the distances.

f

1

=

x

1

+

d−x

1

You will get a quadratic relation between x,

f and d as x

2

- xd + fd = 0 -------(1)

3) Substitute the value of d=100 cm

and f=21 cm to find the value of x.

so when we put f=21 and d=100

finally

Substituting these values in equation 1,

we get x

1

=70 cm and x

2

=30 cm