Chromatic Aberrations

Q. A convex lens of glass has power $P$ in air. If it is immersed in water, its power will be

1. $>P$
2. $<P$
3. Cannot be concluded
4. $P$

Q. The dispersive powers of the materials of two lenses forming an achromatic combination are in the ratio of $4:3$. Effective focal length of the lenses is $+60\text{cm}$, then the focal lengths of the lenses should be

1. $-2\text{cm},25\text{cm}$
2. $20\text{cm},-25\text{cm}$
3. $-15\text{cm},20\text{cm}$
4. $15\text{cm},-20\text{cm}$

Q. If $f_V$ and $f_R$ are the focal lengths of a convex lens for violet and red light respectively and $F_V$ and $F_R$ are the focal lengths of a concave lens for voilet and red light respectively, then we must have

1. $f_V>f_R$ and $F_V>F_R$
2. $f_V<f_R$ and $F_V>F_R$
3. $f_V>f_R$ and $F_V<F_R$
4. $f_V<f_R$ and $F_V<F_R$

Q. Will focal length of a lens for a red light be more, same or less than that for a blue light?

Q. The dispersive powers of crown and flint glasses are $0.02\text{and}0.04$ respectively. In an achromatic combination of lenses the focal length of flint glass lens is $40cm$. The focal length of crown glass lens will be

1. $+10cm$
2. $-20cm$
3. $+20cm$
4. $-10cm$

Q. the diameter of the objective lens of a telescope is 5m and wavelength of light is 6000 Angstrom .The liit of resolution of the telescope is ?

Q. The focal length of a convex lens made of flint glass is $15\text{cm}$. To remove its chromatic aberration, it is placed in contact with a concave lens made of crown glass. Find the focal length of the concave lens. The ratio of dispersive powers of flint glass lens to the crown glass lens is $1.5$.

1. $5\text{cm}$
2. $30\text{cm}$
3. $20\text{cm}$
4. $10\text{cm}$

Q.

Resolving power of a microscope depends on

1. the focal length and aperture of the eye lens
2. the focal length of the objective and the eye lens
3. the aperture of the objective and the eye lens
4. the wavelength of light illuminating the object

Q. The focal length of a lens of dispersive power $0.45$ which should be placed in contact with a convex lens of focal length $84\text{cm}$ and dispersive power $0.21$ to make the achromatic combination from the two lenses (in cm) is

1. $+180\text{cm}$
2. $-180\text{cm}$
3. $+150\text{cm}$
4. $-150\text{cm}$

Q. How does magnifing power get affected on increasing the aperture of the objective lens and why in case of a refracting type telescope???

Q. (i) What is meant by.
(A) Spherical aberration?
(B) Chromatic aberration?
(ii) How can spherical aberration be reduced/minimized? Suggest any one method.

Q. What is chromatic aberration ? How can it be minimized or eliminated ?

Q.

A glass slab, a glass prism, and a convex lens have been prepared from the same transparent material. Then dispersive power is possessed by

1. Only glass slab

2. Only glass prism

3. Both glass slab and glass prism

4. Glass slab, glass prism and convex lens

Q. Amount of light entering into the camera depends upon :

1. focal length of objective lens
2. product of focal length and diameter of the objective lens
3. distance of objective from camera
4. aperture setting of the camera

Q. What is the effect on the fringe width if
the whole apparatus (YDSE) is completely immersed in a liquid of refractive index
μ?
​

Q. The main reason for axial chromatic aberration in the formation of images by a lens is/are:

1. focal length of lens is different for different colors.
2. the material used to make the lens is not uniform.
3. different sections of the lens are of different thickness.
4. all of the above.

Q. Parallel rays of light are focussed by a thin convex lens. A thin concave lens of same focal length is then joined to the convex lens and the result is that :

1. the focal point shifts away from the lens by as mall distance
2. the focal point shifts towards the lens by as mall distance
3. the focal point of lens does not shift at all
4. the focal point shifts to infinity

Q. A simple telescope, consisting of an objective of focal length 60 cm and a single eye lens of focal length 5 cm is focussed on a distant object in such a way that parallel rays emerge from the eye lens. If the object subtends an angle of 2${}^o$ at the objective, the angular width of the image is

1. 10${}^o$
2. 24${}^o$
3. (1/6)${}^o$
4. 50${}^o$

Q. Which of the following will produce greater chromatic aberration?

1. thick lens
2. thin lens
3. both produce equal chromatic aberration
4. insufficient information

Q. A diverging lens of focal length $f_1$ is placed in front of and coaxially with a concave mirror of focal length $f_2$. Their separation is d. A parallel beam of light incident on the lens returns as a parallel beam from the arrangement. Then

1. $d=2|f_2|-|f_1|$
2. if the entire arrangement is immersed in water, the conditions will remain unaltered
3. $d=|f_2|-|f_1|$
4. the beam diameters of the incident and reflected beams must be the same

Q. Two converging lenses of focal lengths $f_1=10cm$ and $f_2=20cm$ are placed at some separation. A parallel beam of light is incident on $1^{st}$ lens. Then

1. For emergent beam from second lens to be parallel, the separation between the lenses has to be $30cm$
2. For emergent beam from second lens to be parallel, the separation between the lenses has to be $60cm$
3. If lenses are placed at such a separation that emergent beam from second lens is parallel, then the emergent beam width is $2cm$ if original beam has a width of $1cm$
4. If lenses are placed at such a separation that emergent beam from second lens is parallel, then the emergent beam width is $4cm$ if original beam has a width of $1cm$

Q. An eye specialist prescribes spectacles having a combination of a convex lens of focal length 40 cmIn contact with a concave lens of focal length 25 cm.The power of this lens combination is

1. +1.5 D
2. -1.5 D
3. +6.67 D
4. -6.67 D

Q. Chromatic aberration(distance between the focal lengths for extreme wavelengths) of a convex lens can be reduced by(Assume lenses are kept in vacuum)

1. Adding a convex lens
2. Adding a concave lens
3. Decreasing focal length by squeezing it
4. Decreasing aperture without changing it curvature

Q. The chromatic aberration due to a lens depends upon:

1. focal length of the lens.
2. dispersive power of the material of the lens.
3. both A and B.
4. none of the above.

Q. A convex lens is dipped in a liquid whose refractive index is equal to the refractive index of the lens. Then its focal length will:

1. Become zero
2. Become infinite
3. Become small, but non-zero
4. Remain unchanged

Q. Path followed by two rays through a thin lens in air are shown. (Assume value of $\mu$ of lens same for both rays) .Optical path followed for two rays from A to B is:

1. Greater in case 1 than 2
2. Greater in case 2 than 1
3. Equal in both the cases
4. Value of $\mu$ is needed to compare

Q. Which of the following has a larger chromatic aberration?

1. crown-glass lens
2. insufficient information
3. flint-glass lens
4. both have equal chromatic aberration

Q. What is the power of concave lens?

1. Positive
2. None
3. Negative
4. Neutral

Q. Which of the following will produce smaller chromatic aberration?

1. thick lens
2. thin lens
3. both will produce equal chromatic aberration
4. insufficient information

Q. The focal length of a convex lens made of flint glass is $15cm$. To remove its chromatic aberration, it is placed in contact with a concave lens made of crown glass. Find the focal length of the concave lens. The ratio of dispersive powers of flint glass to crown glass is $1.5$.

1. $-10cm$
2. $+10cm$
3. $-20cm$
4. $+20cm$