Question

For magnification equal to one, the distance of a
real object from the pole of a concave mirror of focal
length 10 cm should be [NCERT Pg. 314]
(1) 10 cm
(2) 20 cm
(3) 5 cm
(4) 15 cm​

Answer 1

Answer:

20 cm

Explanation:

Real image is formed on same side of object that is u, v, and f, all are negative

u = -x (any positive no.)

v= -x ( as magnification is 1)

f = -10 CM

as magnification formulla

1/v + 1/u= 1/f

1/-x + 1/-x = 1/-10

1/-x + 1/-x = 1/-10

2(1/-x) = 1/ -10

2/-x = 1/-10

2/-x = -1/10

-10*2= -x

-20 = -x

-x = -20

x = 20

Answer 2

Answer:

ans is 20 ( after cross multiplication )