Optics part (1)

Total Questions: 78

1. Which of the following radiations has the highest energy per quantum ? [Uttarakhand P.C.S.(PRE) 2012]

(a) 320-400 nm
(b) 200-280 nm
(c) 280-320 nm
(d) 400-600 nm

Correct Answer: (b) 200-280 nm

Solution:Photon energy is directly proportional to the wave frequency and inversely proportional to the wavelength.
E = hc/λ

E = energy of photon
h = plank constant
c =speed of light in a vacuum
λ = wavelength
Thus, among the given options 200-280 nm radiation has the highest energy per quantum. Ultraviolet radiation contains sufficient energy per quantum to damage living cells. The ultraviolet spectrum is divided into UV-A (320. 400 nm) responsible for tanning the skin; UV-B (280-320 nm) responsible for skin cancer and vitamin D synthesis and UV-C (below 280 nm), potentially the most harmful waveband but absorbed almost completely by molecular oxygen(ozone) in the stratosphere.

2. The visible range of solar radiation is - [53rd to 55th B.P.S.C. (PRE) 2011]

(a) 100-400 nm
(b) 400-700 nm
(c) 740-10000 nm
(d) none of the above

Correct Answer: (b) 400-700 nm

Solution:The electromagnetic spectrum encompasses all the type of radiations. The part of the spectrum that reaches earth from the sun is between 100 nm to 10⁶nm. This band is broken into three ranges- infrared (above 700 nm ), visible (400 to 700 nm ) ultraviolet (below 400 nm ).

3. The wave length extension of visible light is - [U.P.P.C.S.(MAINS)]

(a) between 200-900 nm
(b) between 250-850 nm
(c) between 300-800 nm
(d) between 390-780 nm

Correct Answer: (d) between 390-780 nm

Solution:Visible light is that part of electromagnetic radiations which can be seen by human eyes .Visible light usually defined as having the wavelength in the range of 400-700 nm (4000-7000Å) between the infrared and ultraviolet . A typical human eyes will respond to wavelength from about 380 to 750 nm. Thus among the given option option d will be right answer.

4. The wavelength of visible spectrum is in the range : [63th B.P.S.C. (PRE) 2017]

(a) 1300Å-3900Å
(b) 3000Å-7600Å
(c) 7800Å-8200Å
(d) 8500Å- 9800Å

Correct Answer: (b) 3000Å-7600Å

5. Human eyes is the most sensitive to visible light of the wavelength : [U.P.P.S.C.(R.I.) 2014]

(a) 6050Å
(b) 5500Å
(c) 4500Å
(d) 7500Å

Correct Answer: (b) 5500Å

Solution:Eye is most sensitive to yellowish green light that is light of wavelength about 5550Å or 555nm

6. Among the colour mentioned below the eye is most sensitive to colour between : [U.P.P.C.S.(MAINS) 2008]

(a) red and green
(b) orange and yellow
(c) green and yellow
(d) yellow and green

Correct Answer: (d) yellow and green

Solution:In normal lighting conditions photo receptor cells in human eye are the most sensitive to colour between the wavelength of 530- 570 nanometer. The sensitive of our eyes is the most for yellowish-green colour.

7. Which of the following statement is not correct ? [U.P.R.O./A.R.O.(pre) 2021]

(a) human ear becomes the most sensitive at 1000 hz.
(b) human eyes becomes the most sensitive for red colour .
(c) persistence of hearing is 1/10 second
(d) persistence of vision is 1/16 second

Correct Answer: (b) human eyes becomes the most sensitive for red colour .

Solution:The human ear is most sensitive to sounds between 1000 and 5000 Hz. The human eye is most sensitive to yellowish- green colour. When fully light-adapted, the human eye features a wavelength response from around 400 to 700 nanometers, with a peak sensitivity at 555 nanometers (in the yellowish-green region of the visible light spectrum). The impression of sound heard by our ears persist in our mind for 1/10th of a second.

If another sound is heard before 1/10 second is over, the impression of the two sound mixes up and our mind cannot differentiate among the two. Persistence of vision is a phenomenon of the human eye wherein the image formed on the retina is retained by the brain for 1/16th of a second. Hence, statement of option (b) is incorrect

8. The nature of radiation of light is - [42th B.P.S.C. (PRE) 1997-98]

(a) like wave
(b) like particle
(c) like both of wave and particle
(d) like neither of wave nor of particle

Correct Answer: (c) like both of wave and particle

Solution:The light has a dual nature sometimes it behaves as wave and sometimes as particle. In the later part of the 19th century and in the beginning of 20th century, it was realized that black body radiation and the photoelectric effect can be understood only on the basis of particle model of light.

Some experiments require light to be a wave, while others require light to be a particle. This led to the acceptance of dual nature of light. Quantum mechanics explains the duality of light by describing it as a wave-packet. A wave-packet refers to waves that may interact either as spatially localized, acting as particle, or interacting like waves.

9. Light appears to travel in a straight line because - [U.P.P.S.C.(R.I.) 2014]

(a) it consist of small particles
(b) the velocity of light is very large
(c) the wavelength of light is very small
(d) light is reflected by the surroundings

Correct Answer: (c) the wavelength of light is very small

Solution:Light's wave nature causes it to bend around obstacles (diffraction). However, this bending is only noticeable when the obstacle is comparable in size to the light's wavelength. Visible light has extremely short wavelengths.

This means that for light to noticeably bend around everyday objects, those objects would have to be incredibly tiny. Because most objects we encounter are much larger than the wavelength of light, the bending is negligible, so due to its very small wavelength the light appears to travel in a straight line.

10. Which of the following statement is true ? [U.P. Lower Sub.(PRE) 2022]

(a) The light has a greater velocity
(b) The sound has the greatest velocity
(c) Celestial objects have the greatest velocity
(d) Rocket has the greatest velocity

Correct Answer: (a) The light has a greater velocity

Solution:The speed of light in a vacuum is 3.00 × 10⁸ m/s, while the speed of sound in vacuum is zero and in air is 343 m/sec. The speed of light in glass is 2.0^× 10⁸ m/s. The velocity of light always greater than the velocity of sound. The velocity of celestial objects and the rockets is quite low than the velocity of light.