Question

an object 3cm high is placed at a distance of 20cm in front of convex lense of focal lenght 12cm. find the position nature and size of the image formed​

Answer 1

Explanation:

You just need to be careful on sign convention object distance u is negative in case of lens Please follow me

Answer 2

An object 3 cm high is placed at a distance of 20cm in front of convex lense of focal lenght 12cm.

We have to find the position nature and size of the image formed.

From above data we have; image distance from convex lens (u) is -20 cm, focal length (f) is 12 cm and height of object (h) is 3 cm.

Using lens formula:

1/f = 1/v - 1/u

Substitute the known values,

1/12 = 1/v - 1/(-20)

1/12 = 1/v + 1/20

1/12 - 1/20 = 1/v

1/4(1/3 - 1/5) = 1/v

1/4 [(5 - 3)/15] = 1/v

1/4 (2/15) = 1/v

1/2 (1/15) = 1/v

1/30 = 1/v

On comparing we get,

v = 30 cm

Therefore, the image distance (v) from the lens is 30 cm.

Using magnification formula:

m = v/u = h'/h

(h' = height of image)

Substitute the values,

30/(-20) = h'/3

-3/2 = h'/3

Cross-multiply them

2h' = -9

h' = -9/2

h' = -4.5

Therefore, the height of the image (h') is 4.5 cm.

Nature of the image:

Real, inverted and larger than object. As the image distance from lens is in positive value, means the image is located on the other side of the lens.