Question

Q4. An object is places at a distance of 50 cm from a concave lens of focal length 20 cm. Find the nature
and position of image.

Answer 1

Given :-

▪ An object is placed at a distance of 50 cm from a concave lens of focal length 20 cm.

To Find :-

▪ Nature of image.

▪ Position of image.

Solution :-

We are given,

• Object distance, u = -50 cm
• Focal length, f = - 20 cm

Using the mirror formula, Let us find the position of the image using the lens formula,

⇒ 1/v - 1/u = 1/f

⇒ 1/v - 1/(-50) = -1/20

⇒ 1/v = 1/50 - 1/20

⇒ 1/v = (2 - 5)/100

⇒ 1/v = -3/100

⇒ v = - 100/3

⇒ v = -33.33 cm

Now, Let us find the nature of the image which can be found out by looking at the magnification, which can be calculated as,

⇒ m = v / u

⇒ m = (-33.33) / (-50)

⇒ m = 33.33 / 50

⇒ m = 0.67

Since, The magnification is positive so the image is vertical & erect and smaller in size as compared to object.

Answer 2

Answer:

Given :-

▪ An object is placed at a distance of 50 cm from a concave lens of focal length 20 cm.

To Find :-

▪ Nature of image.

▪ Position of image.

Solution :-

We are given,

Object distance, u = -50 cm

Focal length, f = - 20 cm

Using the mirror formula, Let us find the position of the image using the lens formula,

⇒ 1/v - 1/u = 1/f

⇒ 1/v - 1/(-50) = -1/20

⇒ 1/v = 1/50 - 1/20

⇒ 1/v = (2 - 5)/100

⇒ 1/v = -3/100

⇒ v = - 100/3

⇒ v = -33.33 cm

Now, Let us find the nature of the image which can be found out by looking at the magnification, which can be calculated as,

⇒ m = v / u

⇒ m = (-33.33) / (-50)

⇒ m = 33.33 / 50

⇒ m = 0.67

Since, The magnification is positive so the image is vertical & erect and smaller in size as compared to object.

Explanation:

Hope this answer will help you.✌️