the real image of an object placed at 60 cm from a concave mirror is formed at 20 cm from the mirror find the focal length of the mirror
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According to Mirror's Formula
↓
→ 1/f = 1/u + 1/v
Since Object is always placed on Left Side therefore sign of u will be negative.
In a concave mirror, Real Image is formed in plane of object. Therefore, final sign of v will also be negative.
→ 1/f = 1/(- 20) + 1/(- 60)
→ 1/f = - 1/20 - 1/60
→ 1/f = (- 3 - 1)/60
→ 1/f = - 4/60
→ f = - 60/4 or - 15 cm
Hence Focal Length of Concave Mirror is 15 cm (where negative sign shows that focus lies on left side i.e., plane of object)
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