Sign Convention

Q.

Why the focal length of convex lens is always positive?

Q. A negative magnification indicates that the image is:

1. Erect
2. Diminished
3. Inverted
4. Enlarged

Q.

Does an air bubble inside water behave like a lens? If so, what type of lens is it? Explain?

Q. A thin double convex lens has radii of curvature each of magnitude 40 cm and is made of glass with refractive index 1.65. Its focal length is nearly ___ cm.

Q. Find θ if light is falling on the pole of a concave mirror.

1. 15°
2. 30°
3. 45°
4. 60°

Q.

The lens is made up of which glass

1. Ordinary Glass

2. Pyrex Glass

3. Flint Glass

4. Cobalt Glass

Q. By drawing a neat diagram, describe the image formation by a concave lens when an object is
(a) at infinity.
(b) anywhere between optical centre and infinity.
[5 MARKS]

Q. Assertion (A): The focal length of the concave mirror is negative.
Reason (R): From sign convention, distances measured from pole towards the object are taken as negative.

Q.

What type of lens must be placed at XY so that the image shifts from I to $I^{{}^{\prime }}$?

Q. Find θ if light is falling on the pole of a concave mirror.

Q. Write the rules for sign convention.

Q. In the given setup, consider the case where the first image formed by the plane mirror is taken as an object for the concave mirror. Which of the following can be the correct distance of the image formed by the concave mirror from the pole?

1. $30\text{cm}$
2. $20\text{cm}$
3. $50\text{cm}$
4. $10\text{cm}$

Q. If an object is placed away (at infinity) from the pole of a convex mirror whose focal length is 10 cm, the image is located at .

1. + 10 cm
2. - 10 cm
3. at infinity

Q. An object 5.0 cm in length is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position of the image and height of the image.

1. $v=8.57cm$, $hi=2.14cm$
2. $v=40cm$, $hi=5cm$
3. $v=57cm$, $hi=14cm$
4. $v=4cm$, $hi=2.14cm$

Q. Identify the correct properties and uses of a convex mirror.

1. Wider view
2. Converging
3. Diverging
4. Rearview mirrors
5. Dentist mirrors
6. Shaving mirrors
7. Diminished image
8. Virtual image
9. Erect image

Q. a) For convex lens, distance of real image from the optical centre is .........
b) Focal length of concave lens is ..........

1. $a=positive,b=positive$
2. $a=negative,b=negative$
3. $a=positive,b=negative$
4. $a=negative,b=positive$

Q. When an illuminated object is held in front of a thick mirror several images are formed out of which second image is bright why