Mirror Formula and Magnification

Q. An object of size 50 cm, placed in front of a spherical mirror at 20 cm, forms an image of size 25 cm above the principal axis. Find out the focal length with sign convention and the type of spherical mirror used?

1. – 25 $cm$, concave mirror

2. + 25$cm$, convex mirror

3. + 20 $cm$, convex mirror

4. – 20 $cm$, concave mirror

Q. According to mirror formula, the correct relation between the image distance $\left(v\right)$, object distance $\left(u\right)$ and the focal length $\left(f\right)$ is:

1. $\frac{1}{v}+\frac{1}{u}=\frac{1}{f}$
2. $\frac{1}{v}+\frac{1}{f}=\frac{1}{u}$
3. $\frac{1}{v}+\frac{1}{u}=-\frac{1}{f}$
4. $\frac{1}{v}+\frac{1}{f}=-\frac{1}{u}$

Q.
The above images are that of a specialized slide projector. Slides are small transparencies mounted in sturdy frames ideally suited to magnification and projection, since they have a very high resolution and a high image quality. There is a tray where the slides are to be put into a particular orientation so that the viewers can see the enlarged erect images of the transparent slides. This means that the slides will have to be inserted upside down in the projector tray. To show her students the images of insects that she investigated in the lab, Mrs. Iyer brought a slide projector. Her slide projector produced a 500 times enlarged and inverted image of a slide on a screen 10 m away.

(a) Based on the text and data given in the above paragraph, what kind of lens must the slide projector have?

(b) If v is the symbol used for image distance and u for object distance then with one reason state what will be the sign for $\frac{v}{u}$ in the given case?

(c) A slide projector has a convex lens with a focal length of 20 cm. The slide is placed upside down 21 cm from the lens. How far away should the screen be placed from the slide projector’s lens so that the slide is in focus?
[4 Marks]

Q.

What is magnification in the below diagram?

Given OA = $10cm$ and O’A’ = $2cm$.

1. $5$
2. $-2$
3. $-10$
4. $-0.2$

Q. For an inverted image, the height is taken as

1. positive
2. negative
3. zero
4. undefined

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

Q.

Relate the image distance ($v$), object distance ($u$) , image height ($h^{{}^{\prime }}$) and object height ($h$) to the formula of magnification $\left(M\right)$ for a mirror.

1. $M=\frac{h}{h^{\prime }}$ = $\frac{v}{u}$

2. $M=\frac{h^{\prime }}{h}$ = $\frac{-u}{v}$

3. $M=\frac{h^{\prime }}{h}$ = $\frac{-v}{u}$

4. $M=\frac{h^{\prime }}{h}$ = $\frac{u}{v}$

Q. A telescope made of mirrors is used to observe the moon. It forms the inverted image of the moon at 3.5 km from the eye piece. Find the diameter of the image of the moon. Given the diameter of the moon is 1700 km and the distance of the moon from the earth is 350, 000 km.

1. H = 350, 000 km

2. H = 700 km

3. H = 7 m

4. H = 3.5 km

Q.

Find the focal length of the given mirror.

1. – 30 cm
2. – 20 cm
3. + 20 cm
4. + 30 cm

Q.

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

1. $\frac{-6}{5}cm$

2. $\frac{-5}{6}cm$
3. $\frac{5}{6}cm$

4. $\frac{6}{5}cm$