Question

Find the distance of the image formed when an object placed at 10 centimeter
from the convex lens whose focal length is 4 cm.​

Answer 1

Answer :

• Image distance is 6.67 cm

Explanation :

• Object Position (u) = -10 cm
• Focal length (f) = 4 cm
• Convex Lens

Use lens formula :

1/f = 1/v - 1/u

⇒1/v = 1/f + 1/u

⇒1/v = 1/4 - 1/10

⇒1/v = 10 - 4/40

⇒1/v = 6/40

⇒v = 40/6

⇒v = 6.67

• Image is formed at 6.67 cm

$\rule{150}{0.5}$

Now, use formula for magnification

⇒m = v/u

⇒m = 6.67/-10

⇒m = -0.667

• Magnification is -0.667
• Nature of Image is Real and Inverted

Answer 2

Answer:

Given:-

• u = -10 cm (Object distance is always negative)
• f = 4 cm (The focal length for convex lens is positive)

Formula:-

• The lens formula:- 1/f = 1/v - 1/u

To find:-

• The image distance.

Solution:-

By, 1/f = 1/v - 1/u

➜ 1/4 = 1/v - 1/10

➜ 1/v = 1/4 - 1/10

➜ 1/v = (10 - 4)/40

➜ 1/v = 6/40

➜ 1/v = 3/20

➜ v = 20/3 = 6.667 cm

Let us also find the size and the nature of the image.

Magnification = v/u

➜ 0.15/-10

➜ -0.667

The object size is -0.667.

The image formed is real and inverted.