Name: Sign Convention for Spherical Lenses
Uploaded: 2019-07-19
Duration: 3 min 25 s
Description: Do you know on which side of the lens we should keep the object? There are some conventions that specify things like this. Watch the video to find out what t...

Question

An object of height

5 cm

is placed at a distance of

15 cm

in front of a concave lens of focal length

10 cm

. Use an appropriate scale and draw a ray diagram to obtain the image of the object. What is the size of the image?

Accepted Answer

Given:

Distance of object from lens, $u = - 15 cm$ .

Object height, $h_{o} = 5 cm$ .

Focal length of the concave lens, $f = - 10 cm$ .

Let, $v$ be the image distance from the lens.

We know:

$\frac{1}{f} = \frac{1}{v} - \frac{1}{u} \Rightarrow \frac{1}{- 10} = \frac{1}{v} - \frac{1}{- 15} \Rightarrow \frac{1}{v} = \frac{1}{- 10} - \frac{1}{15} \Rightarrow \frac{1}{v} = - \frac{1}{6} .$

The image distance, $v = - 6 cm$ . The negative sign shows that the virtual image is formed in front of the lens.

Let, $h_{i}$ be the height of the image formed.

We know that,

$m = \frac{v}{u} = \frac{h_{i}}{h_{o}} \Rightarrow \frac{- 6}{- 15} = \frac{h_{i}}{5} \Rightarrow h_{i} = 2 cm .$

The ray diagram is as follows:

Thus, a virtual and erect image is formed at a distance of $6 cm$ in front of the lens and the size of the image is $h_{i} = 2 cm$ .

An object of height $5 cm$ is placed at a distance of $15 cm$ in front of a concave lens of focal length $10 cm$ . Use an appropriate scale and draw a ray diagram to obtain the image of the object. What is the size of the image?

Important Questions on Refraction Through a Lens

Learn and Prepare for any exam you want !

An object of height 5 cm is placed at a distance of 15 cm in front of a concave lens of focal length 10 cm. Use an appropriate scale and draw a ray diagram to obtain the image of the object. What is the size of the image?

Important Questions on Refraction Through a Lens

Learn and Prepare for any exam you want !

An object of height $5 cm$ is placed at a distance of $15 cm$ in front of a concave lens of focal length $10 cm$ . Use an appropriate scale and draw a ray diagram to obtain the image of the object. What is the size of the image?