Lens Formula

Q.

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

1. 60 cm from point B

2. 60 cm from point A

3. 60 cm left of lens

4. 90 cm from point B

Q.

Compare two quantities — Quantity A and Quantity B — and then determine which of the following statements describes the comparison:

In a lens, if
u - distance of the object from the lens
v - distance of the image from the lens
$h^i$ - height of the image
h - height of the object

1. Quantity B is greater.
2. Quantity A is greater
3. The two quantities are equal.
4. The relationship cannot be determined from the information given.

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

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

Q.

OA is an object with image size 4 cm and O'A' is the image of the object. Find the image height and nature of the image formed.

1. 3 cm, erect

2. 2cm, inverted

3. 4 cm, inverted

4. 3cm, inverted

Q. A convex lens forms a real and inverted image. The magnification will be .

1. positive
2. negative
3. zero

Q.

A $10cm$ tall candle, when viewed using a convex lens, appears to be $20cm$ tall. The focal length of the lens is $5cm$. What is the object distance?

1. 10 cm

2. 5 cm

3. 20 cm

4. 2.5 cm

Q.

Which of the following is true about lenses?

1. convex mirror has positive focal length and concave lens have positive focal length

2. both convex mirror and convex lens have negative focal length.

3. convex mirror has positive focal length and concave lens have negative focal length

4. convex mirror has negative focal lengths concave lens have positive focal length

Q.

What is the nature of the lens and the position of the object if the image formed is of the same size as that of the object?

1. concave lens, at 2F₁

2. convex lens, at F₁

3. convex lens, at 2F₁

4. concave lens, at F₁

Q.

An object is placed at $30cm$ in front of the convex lens of focal length $10cm$. Find out the image distance from the lens?

1. -15 cm

2. +20 cm

3. + 15 cm

4. -20 cm

Q. Select the correct lens formula where $u,v,f$ have standard meanings.

1. $\frac{1}{v}-\frac{1}{u}-\frac{1}{f}=0$
2. $\frac{1}{u}-\frac{1}{v}-\frac{1}{f}=0$
3. $\frac{1}{u}+\frac{1}{v}-\frac{1}{f}=0$
4. $\frac{1}{v}+\frac{1}{v}+\frac{1}{f}=0$