11. PYQ - Image formation in concave lens

Question:

5 m.

Section D: Give a long answer to the question given below.

An object is placed at a distance of \(60\ cm\) from the optical centre of a concave lens of focal length \(18\ cm\). Use lens formula to determine the distance of the image from the optical centre of the lens.

We know that the lens formula is

\(\frac{1}{f}\ =\ \frac{1}{v}\ +\ \frac{1}{u}\)
\(\frac{1}{v}\ =\ \frac{1}{f}\ -\ \frac{1}{u}\)
\(\frac{1}{f}\ =\ \frac{1}{v}\ -\ \frac{1}{u}\)
\(\frac{1}{u}\ =\ \frac{1}{f}\ -\ \frac{1}{v}\)

The image distance is \(cm\)

The formula to calculate the magnification is

\(m\ =\ \frac{-v}{u}\)
\(m\ =\ \frac{v}{u}\)
\(m\ =\ v \times u\)
\(m\ =\ \frac{v}{-u}\)

The magnification is

The formed image is

real, inverted and magnified
virtual, erect and diminished
virtual, erect and magnified
real, inverted and diminished

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