The focal length of a plane mirror is:

Two plane mirrors are placed at an angle of $60^\circ$. $A$ horizontal light ray is reflected by the first mirror and then by the second mirror. The total deviation will be ........... $^\circ$.

$A$ man moves towards a plane mirror with a velocity $v$ in a direction making an angle $\theta$ with the normal to the mirror. The magnitude of the velocity of the image relative to the man is:

$A$ point source of light $S$ at a distance $d$ from the screen $A$ produces light intensity $I_0$ at the centre of the screen. If a completely reflecting mirror $M$ is placed at a distance $d$ behind the source as shown in the figure,treating the object and its image as incoherent with each other,find the intensity at the centre of the screen.

$A$ ray of light is incident on a plane mirror at rest. The mirror starts turning at a uniform angular acceleration of $4\pi \, rad/s^2$. The reflected ray at the end of $\frac{1}{4} \, s$ must have turned through......$^o$

$A$ man runs towards a plane mirror at a speed of $15 \, m/s$. The speed of the image relative to the man is $...... \, m/s$.