Question

An object of height 4 cm is placed at a distance of 20
cm from a convex lens of focal length
10 cm. Use lens formula to determine the position of
the image formed

Answer 1

Explanation:

Given that oblect size(h) =4cm

Object distance (u) =20 cm

Focal length (f) =10cm

1/f=1/v+1/u

1/v=1/f-1/u

=1/10-1/20

=1/20=1/v

-V=-20

The screen should be placed at 20cm from the mirror and the image is real.... The image is also Inverted and enlarged...

Answer 2

The image distance from the mirror is -20 cm

Since the image distance is negative. The image is virtual and located at the object side of the lens.

GIVEN

Object height = 4 cm

distance of the object from the mirror = 20 cm

The focal length of the mirror = 10 cm

TO FIND

The position of the image formed

SOLUTION

We can simply solve the above problem as follows -

We are given,

Object height, h0 = 4 cm

Object distance, u = 20 cm

focal length, f = 10 cm

To calculate the image distance from the mirror,

we will apply the mirror formula, which is as follows -

$\frac{1}{f} = \frac{1}{u} + \frac{1}{v}$

putting the values in the formula, we get -

$\frac{1}{10} = \frac{1}{20} + \frac{1}{v}$

$\frac{1}{v} = \frac{1}{10} - \frac{1}{20}$

$\frac{1}{v} = - \frac{1}{20}$

v = -20 cm

Hence the image distance from the mirror is -20 cm

Since the image distance is negative. The image is virtual and located at the object side of the lens.

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