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An object is placed in front of a concave mirror whose radius of curvature is...

Physics
NECO 2005

An object is placed in front of a concave mirror whose radius of curvature is 12cm. If the magnification of the Image produced is 1.5, how far is the object from the mirror?

  • A. 8cm
  • B. 10cm
  • C. 15cm
  • D. 18cm
  • E. 20cm
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Correct Answer: Option B
Explanation

Radius of curvature(r)=12cm

focal length(F) = r ÷ 2 → 12 ÷ 2 = 6cm

therefore F = 6cm

magnification(M) = v ÷ u

1.5 = v ÷ u

:v = 1.5u

Using mirror formula

1/f =1/v + 1/u

\(\frac{1}{6}\) =\(\frac{1}{1.5u}\) + \(\frac{1}{u}\)

\(\frac{1}{6}\) = \(\frac{1 + 1.5}{1.5u}\)

\(\frac{1}{6}\) = \(\frac{2.5}{1.5u}\)

1 * 1.5u = 2.5 * 6

u = \(\frac{15}{1.5}\) = 10

therefore object distance =10cm.


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Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
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WAEC offline past questions - with all answers and explanations in one app - Download for free
WAEC May/June 2024 - Practice for Objective & Theory - From 1988 till date, download app now - 99995
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 24709
Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
WAEC May/June 2024 - Practice for Objective & Theory - From 1988 till date, download app now - 99995
WAEC offline past questions - with all answers and explanations in one app - Download for free