Question

The focal length of a concave mirror is 15 cm. If an object is placed at a distance of 30 cm from the
pole, then its image will be formed
a) at 15 cm and will be erect in nature
(c) at 30 cm and will be erect in nature
If the focal length of the mirror is 17 cm, then the radius of the sphere of which the
and erect
(b) at 30 cm and will be inverted in nature
(d) at 20 cm and will be inverted in nature​

Answer 1

Answer:

• 30cm from the pole it will be real in nature
• Explanation:
• given
• focal length of a plane mirror is(f) =15cm
• object distance(u)=30cm
• image distance(v)=?
• given it is a concave mirror

1. NOTE:In a concave mirror object distance will be opposite side to the incident ray and focus will also be opposite to incident ray.
2. So According To "Sign Conventions" incident ray will be negative and focal length will also  be negative

• from mirror formula
• 1/f=1/u+1/v
• 1/-15=1/-30+1/v
• 1/v=1/-15+1/30
• 1/v=1/30-1/15
• 1/v=$(1-2)/30$
• 1/v=-1/30
• v=-30

Answer 2

Answer:

c.) at 30cm and will be erect in nature