Question

an object 60 cm from lens give a virtual image at a distance of. 20cm in front of the lens . what is the length of the lens ? Is the lens converging or diverging ? Give reason for your answer​

Answer 1

Answer:

Explanation:

Correct Question :-

An object kept at a distance of 60 cm from a lens gives a virtual image at a distance of 20 cm over the same side of the lens. What is the focal length of the lens? Is the lens converging or diverging?

Answer :-

Given :-

u = - 60 cm

v = - 20 cm

To Find :-

Length of the lens and Lens is converging and diverging.

Formula to be used :-

Lens Formula, 1/v - 1/u = 1/f

Solution :-

By applying lens formula, we get

⇒ 1/v - 1/u = 1/f

⇒ 1/f = 1/- 20 - 1/- 60

⇒ 1/f = 1/60 - 1/20

⇒ 1/f = 1 - 3/60

⇒ 1/f = - 2/60

⇒ f = - 60/2

⇒ f = - 30 cm

Hence, the focal length is 30 cm.

The negative sign shows that the lens is diverging.

Answer 2

Explanation:

Correct Question -

An object kept at a distance of 60 cm from a lens give virtual image at a distance of 20 cm over the same side of the lens ? What is the focal length of the lens ? Is the lens converging or diverging ?

Given -

u = -60 cm

v = -20 cm

To Find -

• Focal length of the lens
• Lens is converging or diverging

As we know that,

• 1/f = 1/v - 1/u

here,

f = focal length

v = image distance

u = object distance

Now,

Applying lens formula :-

1/f = 1/(-20) - 1/(-60)

» 1/f = -1/20 + 1/60

» 1/f = -3+1/60

» 1/f = -2/60

» 1/f = -1/30

» f = -30 cm

Hence,

The focal length of the lens is 30 cm

and

The lens is diverging.