Power of a Lens

Q.

A combination of 3 convex lenses is arranged as shown. The focal length of lens I is +5 cm, lens II is +10 cm and lens III is +20 cm. Calculate the total power of the combination of the lens?

1. + 35 D
2. + 75 D
3. -35 D
4. +1 D

Q. What is the nature of the image formed by a convex lens if the magnification produced by the lens is +3?
a) Virtual and diminished
b) Real and erect
c) Real and diminished
d) Virtual and magnified
[1 Mark]

Q.

If lens A has focal length $+15cm$ and lens B has focal length $+30cm$, find out which lens has more power?

1. Lens B has more power

2. Lens A has more power

3. Power of the lens cannot be determined

4. Both have the same power

Q.

Convex lens of focal length 15 cm is kept in series with a concave lens of focal length 30 cm. Find the power of the combination of lenses?

1. 3.33 D

2. + 0.033 D

3. - 0.6 D

4. + 0.6 D

Q. Two thin lenses of focal lengths $f_1$ and $f_2$ are placed in contact with each other. The focal length of the combination will be given by:

1. $\frac{f_1{f}_2}{f_1-f_2}$
2. $\sqrt{f_1{f}_2}$

3. $\frac{f_1{f}_2}{f_1+f_2}$

4. $\frac{f_1+f_2}{2}$

Q.

Negative power indicates that it is a ___.

1. concave lens

2. convex lens

3. combination two convex lenses

4. combination three convex lenses

Q. If f is the focal length of the lens, then the power of a lens is equal to

1. $\frac{100}{f\left(cm\right)}$
2. $\frac{10}{f\left(cm\right)}$
3. $\frac{1}{100f\left(cm\right)}$
4. $\frac{100}{f\left(m\right)}$

Q. The power of three lenses A, B, and C are 1, 2 and 3 dioptre respectively. What is the power of the combination of these lenses?

1. 2 dioptre
2. 6 dioptre
3. 9 dioptre
4. 3 dioptre

Q. The magnification produced by a plane mirror is ___.

1. 2
2. infinite
3. 1
4. 0

Q. Power of a convex lens of focal length 50 cm is ___.

1. -2D
2. -0.5D
3. +2D
4. +0.5D