Question

When a concave mirror is placed facing the Sun, the Sun’s rays converge to a point

10 cm from the mirror. Now, if you place a 2 cm long candles flame 20 cm away on

the principal axis of the mirror, where would you place a screen to obtain the image

of the candle? What would see the size of the image? Draw a ray diagram to justify

your answer.

Answer 1

according to question ,
f = -10 cm
u = -20 cm
height of object = 2 cm
use mirror formula,
1/v + 1/u = 1/f
1/v + 1/(-20) = 1/(-10)
1/v = 1/20 - 1/10
= 1/(-20)
v= -20 cm

magnification= -v/u = height of image /height of object
- (-20)/(-20) = height of image/2 cm
height of image = -2 cm
hence,
image form left side of concave mirror real and same height image form .

Answer 2

Answer:

v = - 20

$\display \text{h _i = -2 cm}$

Explanation:

Given :

Focal length = 10 cm

Object distance = 20 cm

We have image formula :

1 / f = 1 / v + 1 / u

1 / v = 1 / - 10 + 1 / 20

1 / v = - 1  20

v = - 20.

Therefore , screen would be placed at distance of 20 cm to get image.

We have :

m = - v / u = h_i / h_o

- 20 / 20 = h_i / 2

h_i = - 2 cm.

Hence size of the image is 2 cm.