An object is placed at a distance of 40 cm from a concave mirror of focal length 15 cm . If the object is displaced through a distance of 20 cm toward - Physics MCQ NEET (UG) 2018 2026 | ExamTest.live

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An object is placed at a distance of 40 cm from a concave mirror of focal length 15 cm . If the object is displaced through a distance of 20 cm towards the mirror, the displacement of the image will be:

Solution & Step-by-step Explanation

Mirror formula: \frac{1}{v} + \frac{1}{u} = \frac{1}{f} . (Concave mirror: f = - 15 cm)Case 1: u_{1} = - 40 cm $ \frac{1}{v _{1}} + \frac{1}{- 40} = \frac{1}{- 15} $ \frac{1}{v _{1}} = \frac{1}{40} - \frac{1}{15} = \frac{3 - 8}{120} = - \frac{5}{120} v_{1} = - 24 cm Case 2: u_{2} = - 40 + 20 = - 20 cm $ \frac{1}{v _{2}} + \frac{1}{- 20} = \frac{1}{- 15} $ \frac{1}{v _{2}} = \frac{1}{20} - \frac{1}{15} = \frac{3 - 4}{60} = - \frac{1}{60} v_{2} = - 60 cm Displacement = ∣ v_{2} ∣ - ∣ v_{1} ∣ = 60 - 24 = 36 cm .Since the image moved from - 24 to - 60, it moved away from the mirror.

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An object is placed at a distance of 40 cm from a concave mirror of focal length 15 cm . If the object is displaced through a distance of 20 cm towards the mirror, the displacement of the image will be:

30 cm towards the mirror

36 cm away from the mirror

30 cm away from the mirror

36 cm towards the mirror

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