Question

an object of 4 cm height is placed 20 CM from concave mirror which focal length 15 cm find the position nature and size draw a ray diagram​

Answer 1

Generalized mirror equation:

(1 / v) + (1 / u) = (1 / f) = (2 / r).

v = image distance

u = object distance

f = focal distance

r = radius of curvature

Light is incident on the mirror from left to right.

All distances are measured from the pole of mirror.

Distance of any point lying to the left of the pole is negative.

Distance of any point lying to the right of the pole is positive.

Magnification, m is given by (v / u).

If m is positive, image is real. If m is negative, image is virtual.

Object distance is always negative.

Focal distance and radius of curvature of concave mirror are negative.

Here, u = (-15) cm and f = (-20) cm.

So, (1 / v) + {1 / (-15)} = {1 / (-20)}

(1 / v) = (1 / 15) - (1 / 20) = (1 / 60)

v = (+60) cm.

Answer 2

Solution :

• Height = 4 cm
• Focal length = 15 cm
• Distance = 20 cm.

$= > \frac{15}{20} \times 4$

$= > \frac{3}{4} \times 4$

$= > 3 \: \: cm.$