$A$ beam of light incident on a plane mirror forms a real image on reflection. The incident beam is

How are power and focal length of a lens related? You are provided with two lenses of focal length $20\, cm$ and $40\, cm$ respectively. Which lens will you use to obtain more convergent light?

Rays from the Sun converge at a point $15 \, cm$ in front of a concave mirror. Where should an object be placed so that the size of its image is equal to the size of the object?

An object $3.0 \text{ cm}$ high is placed perpendicular to the principal axis of a concave lens of focal length $7.5 \text{ cm}$. The image is formed at a distance of $5.0 \text{ cm}$ from the lens. Calculate $(i)$ distance at which object is placed,and $(ii)$ size and nature of image formed.

The path of a ray of light coming from air passing through a rectangular glass slab traced by four students are shown as $A, B, C$ and $D$ in the figure. Which one of them is correct?

State the sign convention for lenses regarding object and image distances.