$A$ small piece of wire bent into an $L$ shape with upright and horizontal portions of equal lengths,is placed with the horizontal portion along the axis of a concave mirror whose radius of curvature is $10 \, cm$. If the bend is $20 \, cm$ from the pole of the mirror,then the ratio of the lengths of the images of the upright and horizontal portions of the wire is:

The flat bottom of a cylindrical tank is silvered and water $(\mu = 4/3)$ is filled in the tank up to a height $h$. $A$ small bird is hovering at a height $3h$ from the bottom of the tank. When a small hole is opened near the bottom of the tank,the water level falls at the rate of $1\, cm/s$. The bird will perceive that its image's velocity is:

$A$ prism with a refractive index of $1.5$ and an angle $A = 4^o$ is placed in front of a mirror. When the incident ray is reflected by the mirror,what is the total deviation in degrees?

Which of the following form$(s)$ a virtual and erect image for all positions of the object?

In an experiment for the determination of focal length of a convex mirror,a convex lens of focal length $20 \ cm$ is placed on an optical bench and an object pin is placed at a distance $30 \ cm$ from the lens. When a convex mirror is introduced in between the lens and the real and inverted image of the object,the final image of the object $O$ is formed at $O$ itself. If the distance between the lens and the mirror is $10 \ cm$,then the focal length of the mirror is.......$cm$

What is an image?