Question

A concave mirror mounted on a stand is placed along a metre scale at 40cm mark. A Candle flame is at 90cm mark of the scale. The image of the candle flame is seen on the screen which is at 100cm mark of the metre scale.

(a) What is the object distance?

b) What is the image distance?

(c) Find the magnification.

Answer 1

Given info : A concave mirror mounted on a stand is placed along a metre scale at 40cm mark. A Candle flame is at 90cm mark of the scale. The image of the candle flame is seen on the screen which is at 100cm mark of the metre scale.

To find :

• (a) What is the object distance?
• (b) What is the image distance?
• (c) Find the magnification.

solution : concave mirror is placed on a metre scale is at 40 cm mark and a candle is placed at 90 cm mark on the metre scale.

so, distance of candle from the concave mirror = 90cm - 40 cm = 50 cm

therefore the object distance, u = 50 cm

image of candle flame is seen on the screen which is at 100 cm mark on the metre scale.

so, image distance, v = 100cm - 40 cm = 60 cm

here, u = -50 cm , v = - 60cm

[ both object and image are in same side (left side ) so they are negative in sign ]

magnification, m = -v/u = -(-60/-50) = -1.2

Answer 2

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a) It is given that the concave mirror is on 40cm mark and the Object is at 90cm mark, Now the object distance is the distance Between object and mirror. In this case object distance will be = Mark of Object - Mark of concave mirror.

90- 40 = 50cm.

Therefore the object distance is 50cm.

b) Now, we know that the image distance is the distance between mirror and image.

Now, it is given that mirror is on 40cm Mark and the image is seen on 100cm Mark.

Therefore the Image distance will be :

100 - 40 = 60cm.

Image distance = 60cm

c) We know magnification is defined as the ratio of Image distance to Object distance. Therefore the magnification in this case will be :

$m = \frac{ - v}{u}$

$m = \frac{ - 60}{50}$

$m = \cancel \frac{ - 60}{50} = - 1.2$

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BY SCIVIBHANSHU

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