Wave Optics Test

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Wave Optics Test - 34

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Weekly Quiz Competition

Question 1
1 / -0

When a source of light is receding away from an observer, then the spectral lines will get displaced towards

A
violet region

B
red region

C
ultra region

D
blue region

Solution

When an object moves away from us, its light waves are stretched into lower frequencies or longer wavelengths, and we say that the light is redshifted. It also explain the expanding nature of universe.
Shifting towards red end means wavelength is increasing.
Question 2
1 / -0

The limit of resolution of eye is approximately

A
$$1^0$$

B
$$1'$$

C
$$1 mm$$

D
$$1 cm$$

Solution

The resolution of the human eye is the smallest object our eye can see. This is limited by the diffraction limit, which is approximated by the angular size ratio of the object's size versus the distance to the object.
The normal pupil size of a human eye is 4 mm, which sets a minimum angular resolution of the eye and to able to see the small objects we bring them as close to our eyes as possible, but there is a minimum distance for comfortable viewing which is roughly at 25 cm.But quoted figure for the smallest resolvable size is 0.1 mm, showing that the diffraction limit is a crucial factor in visual resolving power.
Question 3
1 / -0

Light waves can be polarised because they

A
have high frequencies

B
have short wavelength

C
are transverse

D
can be reflected

Solution

Polarisation of light waves is possible only because they can oscillate in more than one orientation i.e., they are transverse in nature. It has no dependence on its wavelength and frequencies.
Question 4
1 / -0

Aperture of the human eye is 2 mm. Assuming the mean wavelength of light to be 5000 $$\overset{o}{A}$$, the angular resolution limit of the eye is nearly:

A
2 minute

B
1 minute

C
0.5 minute

D
1.5 minute

Solution

If the angular limit of resolution of human eye is R then
R = $$\displaystyle\frac{1.22\lambda}{a}$$ = $$\displaystyle\frac{1.22 \times 5 \times 10^{-7}}{2 \times 10^{-3}}$$ rad

= $$\displaystyle\frac{1.22 \times 5 \times 10^{-7}}{2 \times 10^{-3}} \times \frac{180}{\pi} \times 60$$ minute = 1 minute
Question 5
1 / -0

An observer on earth observes that wave length of spectral line in spectrum of a milky way shifts towards red end of spectrum. According to the observer, the milky-way is

A
approaching the earth

B
receding away from the earth

C
stationary

D
rotating about its own axis

Solution

When an object moves away from us, its light waves are stretched into lower frequencies or longer wavelengths, and we say that the light is redshifted.
It also explain the expanding nature of universe. Shifting towards red end means wavelength is increasing. There, milkyway is receding away from earth.
Question 6
1 / -0

A satisfactory photographic print is obtained at a distance of 2 m from a 60 Cd lamp when the exposure time is 10s. The time of exposure required for the same quality print at a distance 4 m from a 120 Cd lamp is:

A
5 s

B
10 s

C
20 s

D
25 s

Solution

Amount of light energy coming out from the source in 1st case,, $$I_1 = \displaystyle \frac{L_1}{r_1^2} =\frac{60}{2^2} =15 cd/m^2$$
Amount of light energy coming out from the source in 2nd case,
$$I_2 = \displaystyle \frac{L_2}{r_2^2} =\frac{120}{4^2} =\frac{15}{2} cd/m^2$$
As the quality of photographic print is same, hence
$$I_1t_1 = I_2t_2$$
$$15 \times 10 = \displaystyle \frac{15}{2} \times t^2$$
New exposure time,
$$t_2 = \displaystyle \frac{15 \times 10 \times 2}{15} =20 s.$$
Question 7
1 / -0

The sum of the focal lengths of the objective and an eyepiece, in case of an astronomical telescope. is equal to : (final image is at $$\displaystyle \infty $$)

A
The length of the telescope

B
Half the length of the telescope

C
Double the length of the telescope

D
None of these

Solution

The sum of the focal lengths of the objective and an eyepiece, in case of an astronomical telescope is equal to The length of the telescope.
Question 8
1 / -0

Which of the following phenomena can be demonstrated by light. But not with sound waves in an air column?

A
Reflection

B
Diffraction

C
Refraction

D
Polarization

Solution

As we know the reflection,refraction,diffraction can be demonstrated with sound waves in an air column but to have polarized waves, they first need to be transverse waves but sound waves are longitudinal.Sound waves are longitudinal so they cannot be polarised.
Question 9
1 / -0

A source of light suspended above a circular table at a height equal to the radius of the table gives an intensity I at the centre of the table, the intensity at the edge of the table would be (Assuming illuminance remains the same)

A
0.25 I

B
0.5 I

C
0.7 I

D
2.8 I

Solution

Intensity = I when distance = r
The distance between the source and the edge of the table is $$ r'$$$$= \sqrt{r^2 + r^2} = \sqrt{2r}$$
$$\because I \propto \displaystyle \frac{1}{r'^2}$$
$$\therefore I' \propto \displaystyle \frac{1}{(\sqrt{2 r})^2} \propto \frac{1}{2r^2}$$
$$\therefore I' = 0.5 I$$
Question 10
1 / -0

Which of the following phenomena can be demonstrated by light. But not with sound waves in an air column ?

A
Reflection

B
Diffraction

C
Refraction

D
Polarization

Solution

To have polarized waves, they first need to be transverse waves - the disturbance needs to be at right angles to the direction of propagation. Therefore sound waves in air (the usual sort) or in other gases and liquids can't be polarized because they're purely compressive.
Hence, option D is correct.

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Wave Optics Test - 34

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Wave Optics Test - 34

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SHARING IS CARING

Question 1

violet region

red region

ultra region

blue region

Solution

Question 2

$$1^0$$

$$1'$$

$$1 mm$$

$$1 cm$$

Solution

Question 3

have high frequencies

have short wavelength

are transverse

can be reflected

Solution

Question 4

2 minute

1 minute

0.5 minute

1.5 minute

Solution

Question 5

approaching the earth

receding away from the earth

stationary

rotating about its own axis

Solution

Question 6

5 s

10 s

20 s

25 s

Solution

Question 7

The length of the telescope

Half the length of the telescope

Double the length of the telescope

None of these

Solution

Question 8

Reflection

Diffraction

Refraction

Polarization

Solution

Question 9

0.25 I

0.5 I

0.7 I

2.8 I

Solution

Question 10

Reflection

Diffraction

Refraction

Polarization

Solution

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