Power and Thin Lenses in Contact

Q. A lens of power + 2 diopters is placed in contact with a lens of power – 1 diopter. The combination will behave like

1. A convergent lens of focal length 50 cm
2. A divergent lens of focal length 100 cm
3. A convergent lens of focal length 100 cm
4. A convergent lens of focal length 200 cm

Q.

Two lenses with powers; 2D & -4D are kept together. What is the effective focal length of the combination?

1. 40 cm

2. -50 cm

3. 100 cm

4. 50 cm

Q.

The magnitude of the focal length of a diverging less is 20 cm. What is the power of this lens?

1. 5D

2. 2.5D

3. -5D

4. -2.5D

Q.

Two lenses with powers; 2D & -4D are kept together. What is the effective focal length of the combination?

1. 40 cm

2. -50 cm

3. 100 cm

4. 50 cm

Q. The distance between an object and the screen is 100 cm. A lens produces an image on the screen when placed at either of the positions 40 cm apart. The power of the lens is

1. 3D
2. 5D
3. 7D
4. 9D

Q. The distance between an object and the screen is 100 cm. A lens produces an image on the screen when placed at either of the positions 40 cm apart. The power of the lens is

1. 3D
2. 5D
3. 7D
4. 9D

Q.

The magnitude of the focal length of a diverging less is 20 cm. What is the power of this lens?

1. 5D

2. 2.5D

3. -5D

4. -2.5D

Q. A lens of power $+2.0\text{D}$ is placed in contact with another of power $-1.0\text{D}$. The combination will behave like

1. A converging lens of focal length $100\text{cm}$
2. A diverging lens of focal length $100\text{cm}$
3. A converging lens of focal length $50\text{cm}$
4. A diverging lens of focal length $50\text{cm}$