Question

An object is placed at a distance of 60 cm from a cancave lens of focal length 30cm find the distance of image ​

Answer 1

Answer:

An object is placed at a distance of 60cm from a concave lens of focal length 30cm.

(i) Use the lense formula to find the distance of the image from the lens.

(ii) List four characteristics of the image (nature , position , size , erect / inverted) formed by the lens in the case.

(iii) Draw a ray diagram to justify your answer of the part (ii).

Explanation:

Solution:

We have,

(i) Object distance, u = - 60cm Focal length

f the concave lens, f = - 30cm Using lens

formula,

1 _ 1 _ = 1

v u f

1 = - 1 _ 1

v 30 60

1 _ -3

v 60

V = 20cm

The image will be formed at a distance of 20cm infront of the lens.

(ii) Nature of the image is virtual. The position of image between F1 and optical centre 0. Size of the image is diminished. The image Erect.

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Answer 2

Answer:

Explanation:

Given :

• Object distance (u) = -60 cm
• Focal length (f) = -30 cm

To Find :

• Image distance, v

Formula to be used :

• 1/v - 1/u = 1/f

Solution :

★Image distance,

1/v - 1/u = 1/f

⇒ 1/v - 1/(-60) = 1/(-30)

⇒ 1/v + 1/60 = 1/-30

⇒ 1/v = 1/-30 - 1/60

⇒ 1/v = 1/-20

⇒ v = -20 cm

Hence, Object distance is -20 cm.