A real object is placed in front of a convex lens of focal length $f$ at its principal focus. Then the image is formed at

zero

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Infinity

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at a distance

2 f

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at a distance

\frac{f}{2}

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Solution

The correct option is B Infinity
The object is placed at focus so $u = - f$
For lens formula $\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$
$\frac{1}{f} = \frac{1}{v} - \frac{1}{- f}$
$\frac{1}{v} = 0$

Hence, $v = \infty$ , the image is formed at infinity.

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A real object is placed in front of a convex lens of focal length f at its principal focus. Then the image is formed at

The correct option is B InfinityThe object is placed at focus so u=−fFor lens formula 1f=1v−1u1f=1v−1−f1v=0Hence, v=∞, the image is formed at infinity.

A real object is placed in front of a convex lens of focal length $f$ at its principal focus. Then the image is formed at

The correct option is B Infinity
The object is placed at focus so $u = - f$
For lens formula $\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$
$\frac{1}{f} = \frac{1}{v} - \frac{1}{- f}$
$\frac{1}{v} = 0$

Hence, $v = \infty$ , the image is formed at infinity.