Question

*Physics: 1. Find v, h' & m when object of height 8 cm is placed at 40 cm from a concave mirror of focal length 30cm.* *2. Four times enlarged and real image is formed when an object is placed at 50cm in front of a concave mirror. Find image distance, focal length and nature of image.*​

Answer 1

Answer:

given , object height= 8cm

focal length of concave mirror (f)= (-30cm)

object distance (u) = (-50cm)

1/f=1/u + 1/v

= 1/f - 1/u = 1/v

= 1/(-30) - 1/(-50) = 1/v

= -1/30 - (-1/50) = 1/v

= -1/30 + 1/50 = 1/v

= (-5+3)/150 = 1/v

-2/150 = 1/v

-1/75 = 1/v

v=(-75) cm

therefore screen must be placed at 75 cm in front of mirror for a sharp image. the image is real and inverted.

now , image height / object height = -v/u

= image height / 8 = -(-75)/-50

= image height / 8 = -3/2

= image height = (-3 x 8)/2

=image height = -12 cm

therefore , the image is 12 cm in size , real and inverted.

Answer 2

GIVEN

• Size of object = 2cm
• Object distance, u = -15 cm
• Focal length, f = -10 cm

Applying mirror equation,

1/v +1/u = 1/f

to find out the image distance v = -30 cm using sign convention.

• Using the formula of magnification for mirrors,

m = -v/u

magnification = -2

• As magnification is greater than 1, the image is magnified and as it is negative it is real and inverted.
• Also by using the formula of magnification, we get the size of image as 4 cm.