Question

the distance of the real image of an object and object from the focus of a concave mirror are respectively b and a . find the focal length of the concave mirror in terms of a and b​

Answer 1

Explanation:

Correct option is

D

2

x

1

Let f be focal length

v=

−(x

2

+

f)

u= −(x

1

+ f)

From mirror formula,

v

1

+

u

1

=

f

1

x

2

−1

+

x

1

−1

=

f

−1

(x

1

+f)(x

2

+f)

2

x

1

=

f

1

(x

1

+

x

2

2f)f= (x

1

+ f)(x

2

+ f)

(x

1

+

x

2

2f

2

=

2

x

1

(x

1

+

x

2

f 2

f

2

=

2

x

1

f=

2

x

1

Option D is correct

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