Question

z- An object is placed at
a distance
of 10cm from concave mirror of
Focal length 20cm. Find the
Find the distance
of image
​

Answer 1

Given :-

• Object distance (u) = - 10cm
• Focal length (f) = - 20cm

To find :-

• Image distance (v)

Solution :-

✪ According to the Mirror formula ✪

➪ 1/v + 1/u = 1/f

➪ 1/v = 1/f - 1/u

➪ 1/v = -1/20 - (-1)/10

➪ 1/v = - 1/20 + 1/10

➪ 1/v = -1 + 2/20

➪ 1/v = 1/20

➪ v = + 20cm

Hence,

• Image distance = + 20cm
• Nature of image = Virtual and erect

Note : -

• Magnification of Mirror = -v/u = hi/ho
• Magnification of Lens = v/u = hi/ho
• Lens Formula = 1/v - 1/u = 1/f

Answer 2

Explanation:

Given that an object is placed at a distance of 10cm from concave mirror of focal length 20cm.

We have to find the distance of the image.

From above data we have; u is -10 cm and f is -20 cm.

Using mirror formula:

1/f = 1/v + 1/u

Substitute the values,

→ 1/(-20) = 1/v - 1/(-10)

→ -1/20 = 1/v + 1/10

→ -1/20 - 1/10 = 1/v

→ (-1 + 2)/20 = 1/v

→ 1/20 = 1/v

Cross-multiply it

→ v = 20 cm

Hence, the image distance from the mirror is 20 cm. (Image formed is bigger in size than object and in upward direction).