Question

A 5.0 cm object is 6.0 cm from a convex lens, which has a focal length of 7.0 cm.

Answer 1

The distance of the image from the lens is -42 cm

The height of the image is 35 cm

Answer 2

Answer : The distance of the image from the lens is, -42 cm

The height of the image is, 35 cm

Solution :

First we have to calculate the image distance.

Formula used :

$\frac{1}{f}=\frac{1}{p}+\frac{1}{q}$

where,

f = focal length = 7 cm

p = object distance = 6 cm

q = image distance = ?

Now put all the given values in the above formula, we get the distance of the image from the lens.

$\frac{1}{7cm}=\frac{1}{6cm}+\frac{1}{q}$

$q=-42cm$

Therefore, the distance of the image from the lens is, 42 cm and the negative sign indicates that the image is virtual.

Now we have to calculate the height of the image.

Formula used :

$\frac{h}{h'}=\frac{p}{q}$

where,

h = height of object = 5 cm

h' = height of image = ?

Now put all the given values in this formula, we get the height of the image.

$\frac{5cm}{h'}=\frac{6cm}{-42cm}=-35cm$

Therefore, the height of the image is, 35 cm and the negative sign indicates that the image is inverted.