Question

When a concave mirror is placed facing the sun the sun rays converge to a point 10 cm from the mirror.now if you place 2 cm long candles flame 20 cm away on the principal axis of the mirror ,where would you place screen to obtain the image of the candle ? What would be the size of the image ? Draw a ray diagram to jastify your answer .

Answer 1

Given that a concave mirror converges the sun rays at a point 10cm from the mirror.

Hence the focal length of the concave mirror is
= 10 cm

f = -10 cm
u = -20 cm
h₁ = 2 cm

Using mirror formula ;

(1/f) = (1/v)+(1/u)
1/-10 = (1/v) - (1/20)
(1/v) = (1/20)-(1/10)
1/v = -1/20

v = -20 cm
____________________

m = -v/u = h₂/h₁
-(-20)/(-20) = h₂/2
h₂ = -2 cm
_____________________
Hence we will place the screen at 20cm from the mirror to obtain the image.
And the size of the image is 2cm ,i.e equal but inverted

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.