$A$ lamp is hanging at a height of $40\, cm$ from the center of a table. If its height is increased by $10\, cm$,the illuminance on the table will decrease by what percentage?

The inverse square law for illuminance is valid for:

$A$ $2\,m$ long scale with a least count of $0.2\,cm$ is used to measure the locations of objects on an optical bench. While measuring the focal length of a convex lens, the object pin and the convex lens are placed at $80\,cm$ mark and $1\,m$ mark, respectively. The image of the object pin on the other side of the lens coincides with the image pin that is kept at $180\,cm$ mark. The $\%$ error in the estimation of focal length is

When light is incident on a medium at angle $i$ and refracted into a second medium at an angle $r$,the graph of $\sin i$ vs $\sin r$ is as shown in the figure. From this,one can conclude that:

For a candle of $40$ power,the exposure time required for a photographic print at a distance of $0.6 \, m$ is $20 \, s$. What will be the exposure time required for the same print at a distance of $1.2 \, m$ using a candle of $20$ power?

$A$ point object $O$ is moving towards a concave mirror as shown in the figure. Choose the correct option representing the direction of the velocity of the image ($F$ is the focus and $C$ is the centre of curvature).