Light – Reflection and Refraction

Class 10 NCERT Science

NCERT

1   Define the principal focus of a concave mirror.

Solution :

Light rays that are parallel to the principal axis of a concave mirror converge at a specific point on its principal axis after reflecting from the mirror. This point is known as the principal focus of the concave mirror.

2   The radius of curvature of a spherical mirror is $20 cm$. What is its focal length?

Solution :

Radius of curvature, $R = 20 cm$$\\$ Radius of curvature of a spherical mirror $= 2 ×\text{ Focal length (f)}$$\\$ $R = 2f$$\\$ $f = R/2 = 20/2 = 10 cm$$\\$ Hence, the focal length of the given spherical mirror is $10 cm.$

3   Name the mirror that can give an erect and enlarged image of an object.

Solution :

When an object is placed between the pole and the principal focus of a $\underline{\text{concave mirror,}}$ the image formed is virtual, erect, and enlarged.

4   Why do we prefer a convex mirror as a rear-view mirror in vehicles?

Solution :

Convex mirrors give a virtual, erect, and diminished image of the objects placed in front of it. They are preferred as a rear-view mirror in vehicles because they give a wider field of view, which allows the driver to see most of the traffic behind him.

5   Find the focal length of a convex mirror whose radius of curvature is $32 cm.$

Solution :

Radius of curvature, $R = 32 cm$$\\$ Radius of curvature $ = 2 ×\text{ Focal length (f)}$$\\$ $R = 2f$$\\$ $f = R/2 = 32/2 = 16cm$$\\$ Hence, the focal length of the given convex mirror is $16 cm.$