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Light Reflection and Refraction
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02/12/2020 10:50 am
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An object 2 cm in size is placed 30 cm in front of a concave mirror of focal length 15 cm. At what distance from the mirror should a screen be placed in order to obtain a sharp image? What will be the nature and the size of the image formed? Draw a ray diagram to show the formation of the image in this case.
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02/12/2020 10:55 am
f = -15 cm, h0 = 2 cm, u = -30 cm
Using, 1/f = 1/v + 1/u, we get
1/v = 1/f - 1/u = 1/-15 - 1/-30
= 2 -1/-30 = 1/-30
⇒ v = -30 cm
So, screen should be placed at a distance of 30 cm on the same side of the object in order to obtain a sharp image.
Since, |v| = |u| = 2f, it means that the object is placed at the centre of curvature (C) of a concave mirror, the image formed is at centre of curvature, real and inverted and of the same size as the object.