Question

at what distance from a concave mirror of focal length 10 centimetre should an object 2 centimetre long be placed in order to get An erect image 6 CM tall

Answer 1

Heya

Focal length = -10cm

Height of object = 2cm

Height of image = 6cm

Magnification = height of object /height of image = -image distance/object distance

-v/u= hi/ho

-v/u = 6/2

-v/u = 3

v = -3u

•Mirror formulae

1/f = 1/v + 1/u

-1/10 = 1/-3u +1/u

-1/10 = (-1+3)/3u

-1/10 = 2/3u

-10 = 3u/2

-20/3 = u

=> u=-6.7

The object should be placed at a distance of 6.7cm from the concave mirror

Answer 2

Answer:

Explanation:

Focal length, f: -10cm

Image distance,v: -20cm

1/f = 1/v + 1/u

1/-10 = 1/-20 + 1/u

-1/10 = -1/20 + 1/u

-1/10 + 1/20 = 1/u

-2+1/20 = 1/u

-1/20 = 1/u

u =-20

Therefore, Object distance is 20cm from the mirror