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An object placed at 20 cm in front of a concave mirror produces three times magnified real image. What is the focal length of the concave mirror?
Options
(a) 15 cm
(b) 6.6 cm
(c) 10 cm
(d) 7.5 cm
Correct Answer:
15 cm
Explanation:
We know that, linear magnification, m = f / (f -u) —-(i)
Given, object displaced, u = -20 cm
m = -3 (All real images are inverted)
Substituting the above values in equation (i), we get
-3 = f / [f – (-20)]
⇒ -3f – 60 = f 4f = -60
⇒ f = – 60 / 4 = -15 cm
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Topics: Ray Optics
(94)
Subject: Physics
(2479)
Important MCQs Based on Medical Entrance Examinations To Improve Your NEET Score
- For a thermocouple, the neutral temperature is 270⁰C when its cold junction is at 20⁰C.
- In the series resonance the value of impedence is 3 Ω and the resistance is 4Ω,
- The thermo e.m.f. E in volts of a certain thermocouple is found to vary
- If force(F),length(L) and time(T) be considered fundamental units, then the units of mass
- A transformer rated at 10 kW is used to connect a 5 kV transmission line to a 240 V
Topics: Ray Optics (94)
Subject: Physics (2479)
Important MCQs Based on Medical Entrance Examinations To Improve Your NEET Score
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