Mirror Equations and Focal Length

Q.

In order to produce an image with magnification m, a concave mirror of focal length f is used. If the object is kept at a distance d from the mirror, then $(m–1)f$ equals

1. $md$

2. $\frac{m}{(d+1)}$

3. $\frac{m}{d}$

4. $\frac{1}{md}$

Q. The image formed by a convex mirror is only one-third of the size of the object. If the focal length of the mirror is $12\text{cm}$, then the position of the image formed will be

1. $8\text{cm}$ behind the mirror
2. $10\text{cm}$ behind the mirror
3. $8\text{cm}$ in front of the mirror
4. $10\text{cm}$ in front of the mirror

Q.

Find out the image position formed by concave mirror, considering the image formed by plane mirror as an object for concave mirror.

1. $30cm$, from the pole

2. $40cm$, from the pole

3. $60cm$, from the pole

4. $20cm$, from the pole

Q. An object is placed at a distance of 20 cm in front of a concave mirror of focal length 10 cm. Calculate the magnification of the image produced by the mirror.

1. +½
2. -½
3. +1
4. -1

Q. A point object is placed at a distance of 30 cm from a convex mirror of focal length 30cm. The image will form at

1. Infinity
2. 15 cm infront of the mirror
3. 15 cm behind the mirror
4. 20 cm infront of the mirror

Q. An object 2 cm high is placed at a distance of 16 cm from a concave mirror, which produces a real image 3 cm high. What is the focal length of the mirror ?

1. -9.6 cm
2. -8.3 cm
3. -6.3 cm
4. -3.6 cm

Q.

A 5.0 cm tall light bulb has placed a distance of 50 cm from a convex mirror having a focal length of 10 cm. What is the image height?

1. 6/5 cm

2. -6/5 cm

3. -5/6 cm

4. 5/6 cm

Q.

If AB is an object, CD is an image formed. If AP is object distance CP is image distance from the mirror. Then choose the correct sign convention.

1. height of image = + ve 2. height of image = – ve

3. height of object = + ve 4. height of object = – ve

5. AP = + ve 6. AP = – ve

7. PC = + ve 8. PC = – ve.

1. concave mirror – 1, 3, 5 & 7, plane mirror – 1, 3, 5, 7

2. concave mirror – 2, 3, 6 & 8, plane mirror – 1, 3 , 6 , 7

3. concave mirror – 2, 3, 6 & 8, plane mirror – 1, 3, 6, 8

4. concave mirror – 2, 3, 5, 7, plane mirror – 1, 3, 6,

Q.

A 1 cm tall light bulb is placed at a distance of 50 cm from a convex mirror having a focal length of 10 cm. The height of the image is:

1. 6/5 cm

2. -6/5 cm

3. -5/6 cm

4. 5/6 cm

Q. An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position of the image.

1. 6 cm
2. - 6 cm
3. 30 cm
4. - 30 cm

Q.

The focal length of the convex lens is 20 cm and focal length of the concave mirror is 30 cm. And the separation between lens and mirror is 90 cm. If the object is placed 60 cm before the lens, find out the position of the image formed by the concave mirror.

1. 60 cm left of lens

2. 60 cm from point B

3. 60 cm from point A

4. 90 cm from point B

Q.

A point object is placed at a distance of 30 cm from a convex mirror of focal length 30 cm. The image will form at

1. infinity

2. 15 cm infront of the mirror

3. 20 cm infront of the mirror

4. 15 cm behind the mirror

Q. An object is placed in front of a convex mirror at $60m$ from the mirror. Its radius of curvature is $40m$. The object starts moving towards the mirror at $20m{s}^{-1}$. Find the average speed of the image after a time interval of 2 seconds?

1. $10m{s}^{-1}$
2. $20m{s}^{-1}$
3. $5m{s}^{-1}$
4. $2.5m{s}^{-1}$

Q. If AB = 10 cm & DB = 40 cm (diameter). What is the radius of curvature and the focal length of the spherical glass respectively?

1. 40 cm, 10 cm
2. 40 cm, 5 cm
3. 20 cm, 20 cm
4. 20 cm, 10 cm

Q. A real image of half the size is obtained in a concave spherical mirror with a radius of curvature of 40 cm. The distance of the object and that of its image from the mirror will be respectively

1. 15 cm, 30 cm
2. 30 cm, 15 cm
3. 30 cm, 60 cm
4. 60 cm, 30 cm

Q. The image of an object placed on the principal axis of a concave mirror of focal length 12 cm is formed at a point which is 10 cm more distant from the mirror than the object. The magnification of the image is

1. 2
2. 1.5
3. 1
4. 2.5

Q. An object 20 cm from a convex mirror give rise to a virtual image 15 cm behind the mirror. The focal length of the mirror is

1. 8.5 cm
2. 30 cm
3. 90 cm
4. 60 cm

Q. An object is placed at $60cm$ from the pole of a concave mirror whose focal length is $20cm$. Find the distance at which the image is formed.

1. $v=–20cm$
2. $v=+30cm$
3. $v=+20cm$
4. $v=–30cm$

Q.

An object is placed at 60 m in front of a concave mirror. If its radius of curvature is 20 m, then the image distance is equal to ___ m.

Q. An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image.

Q. A real image of half the size is obtained in a concave spherical mirror with a radius of curvature of 40 cm. The distance of the object and that of its image from the mirror will be respectively

1. 15 cm, 30 cm
2. 30 cm, 15 cm
3. 30 cm, 60 cm
4. 60 cm, 30 cm

Q.

An object is placed at a distance of 10 $cm$from a concave mirror of radius of curvature 0.6 $m$. Which of the following statement is incorrect?

1. The image is formed at a distance of 15 $cm$ from the mirror.

2. The image formed is real.

3. The image is 1.5 times the size of the object.

4. The image formed is virtual and erect.