Question

to form a real image at a distance of 40 cm where should an object be placed in front of a concave mirror of focal length 10 centimetre​

Answer 1

Answer:40 cm away from the concave mirror

Explanation:

Answer 2

Let v be image distance

      u be object distance

      f be focal length

Hence in this case,

v = -40cm   (-ve sign indicates that image is real)

u = ?

f = -10cm     (Focal length is -ve for concave mirror)

Using mirror formula,

1/v + 1/u = 1/f

1/u = 1/f - 1/v

1/u = -1/10 - -1/40

1/u = 1/40 - 1/10

1/u = (1-4)/40 = -3/40

u = -40/3cm

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