Principal Focus and Focal Length of a Mirror

A student determines the focal length of a device $X$, by focussing the image of a far off object on the screen positioned as shown in the figure below.

What is the focal length of the device $X$?

What arrangement should be done by a student to find the focal length of a concave mirror by obtaining an image of a distant object?

A student has to do the experiment on finding the focal length of a given concave mirror, by using a distant object. What set of apparatus should be used by him?

What is the focal length of a concave mirror in the experiment set up shown below?

The image of a distant object is obtained on a screen by using a concave mirror. Which distance should be measure to determine the focal length of the mirror?

The radius of curvature of a spherical mirror is $20 \mathrm{cm}$. What is its focal length?

What is the relation between focal length and radius of curvature of a mirror?

Focal length of a convex mirror is $15 \mathrm{cm}$. What is its radius of curvature?

The radius of curvature of a spherical mirror is $40 \mathrm{cm}$. What is its focal length?

Define the focus of the concave mirror.

Rays from sun converge at a point $10 \mathrm{cm}$ in front of a concave mirror. Where should be an object placed so that size of its image is equal to the size of the object? 

A student determines the focal length of a device X, by focussing the image of a far off an object on the screen positioned as shown in the figure below. 
What is the focal length of the device X?