Focus And Focal Length

Question 1

State the laws of reflection of light for spherical mirrors

Answer 1

The laws of reflection of light are:

• The angle of incidence is equal to the angle of reflection
• The incident ray, the normal and the reflected ray at the point of incidence ,all lie in the same plane

Question 2

State the characteristics of reflected ray for convex and concave mirrors

Answer 2

The reflected rays are not parallel to each other but converge at a point in concave mirror and diverge from a point in convex mirror

Question 3

What is the focus of the concave mirror?

Answer 3

In the case of a concave mirror, the reflected rays meet at a point on the principal axis. This point is called the focus of a concave mirror.

Question 4

What is the focus of a convex mirror?

Answer 4

In the case of a convex mirror, the reflected rays don’t meet at a point but appear to come from a point on the principal axis, behind the mirror. This is called the focus of a convex mirror

Question 5

The focus of a concave mirror is _______ while the focus of a convex mirror is _______

Answer 5

Real, virtual

Question 6

What is the focal length of the mirror?

Answer 6

The distance of the focus from the pole of the mirror is called the focal length of the mirror. It is represented by PF

Question 7

What is the relationship between focal length and radius of curvature??

Answer 7

Focal length = 1/2* radius of curvature
Radius of curvature= 2* Focal length

Question 8

What are the rules for making a ray diagram in a spherical mirror?

Answer 8

1. The object is kept on the left side of the mirror
2. The object is always kept on the principal axis such that it is perpendicular to the principal axis
3. For construction of a diagram , take at least 2 rays of convenience whose paths can be traced after reflection.