Image in Thin Lens by Ray Tracing

Q. A thin lens has focal length f and aperture radius r. It forms an image of intensity I. Now the central part of the aperture upto $\frac{r}{2}$ is blacked by an opaque material. The focal length and intensity of image will be

1. $\frac{f}{2}\&\frac{I}{2}$
2. $f\&\frac{I}{4}$
3. $\frac{3f}{4}\&\frac{I}{2}$
4. $f\&\frac{3I}{4}$

Q. A beam of light converges to a point $P$. A concave lens of focal length $16cm$ is placed in the path of the convergent beam $12cm$ from $P$. How far from the lens does the beam converge?

1. $12cm$
2. $7.5cm$
3. $36cm$
4. $48cm$

Q.

A convex lens A of focal length 20 cm and a concave lens B of focal length 5 cm are kept along the same axis with a distace d between them. If a parallel beam of light falling on A leaves B as a parallel beam, then d is equal to
(IIT-JEE 1985)

1. 5 cm

2. 10 cm

3. 15 cm

4. zero

Q.

A screen is placed at a distance 40 cm away from an illuminated object. A converging lens is placed between the source and the screen and it is attempted to form the image of the source on the screen. If no position could be found, the focal length of the lens

1. Must be less than 10 cm

2. Must be greater than 10 cm

3. Must not be greater than 20 cm

4. Must not be less than 10 cm

Q.

A screen is placed at a distance 40 cm away from an illuminated object. A converging lens is placed between the source and the screen and it is attempted to form the image of the source on the screen. If no position could be found, the focal length of the lens

1. Must be less than 10 cm

2. Must be greater than 10 cm

3. Must not be greater than 20 cm

4. Must not be less than 10 cm

Q. The sun's diameter is $1.4\times {10}^{9}m$ and its distance from the earth is ${10}^{11}m.$ The diameter of its image, formed by a convex lens of focal length 2m will be

1. 0.7 cm
2. 1.4 cm
3. 2.8 cm
4. Zero (i.e. point image)

Q.

To solve a problem using lens formula, if object distance, focal length and height of the object is given, the height of the image can be calculated.

1. Always false

2. Always true

3. Sometimes true

4. Sometimes false