Wave Optics Test

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Wave Optics Test - 35

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Weekly Quiz Competition

Question 1
1 / -0

A plane wavefront $$AB$$ incident on a concave mirror as shown. Then, the wavefront just after reflection is

A

B

C

D
None of the above

Solution

After reflection, every point on the mirror acts as a secondary source resulting in secondary wavefront as shown in figure.
Question 2
1 / -0

Which of the following is a unit for intensity of light?

A
Candle power

B
Lux

C
Both A & B

D
None of the above

Solution

In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye. The SI unit of luminous intensity is the candela (cd), an SI base unit.
Also, unit for intensity of light are:
(i) Candle Power
(ii) Lux
Question 3
1 / -0

The magnifying power of an astronomical telescope is $$8$$, then the ratio of the focal length of the objective to the focal length of the eyepiece is : (final image is at $$\displaystyle \infty $$)

A
$$8$$

B
$$\displaystyle \frac { 1 }{ 8 } $$

C
$$0.45$$

D
None of these

Solution

magnifying power of telescope (M P)$$=8$$
The magnifying power of an astronomical telescope is $$=\cfrac{focal \ length \ of \ object (-f_0) }{focal \ length \ of \ eyepiece(f_e)}=8$$
hence, the ratio of the focal length of the objective to the focal length of the eyepiece is $$8$$.
Question 4
1 / -0

Which of the following statements applies to light?

A
Light can only be described as particles.

B
Light can only be described as waves.

C
Light can be described as rays, waves and particles.

D
Light can only be described as rays.

Solution

We can observe various phenomenon of light which cannot be explained by wave nature of light and photon nature of light some of the phenomenon are listed below:
Nature of light:                                          Phenomenon:
Ray                                                                 Reflection, Refraction
Wave                                                               Diffraction, Interference
Particle                                                  Oscillation frequency of radio waves.
Question 5
1 / -0

A photographer changes the aperture of his camera and reduces it to half of the original aperture. The exposure time now should be:

A
same as before

B
double than before

C
four times than before

D
half than before

Solution

Answer is D.

The amount of light captured while taking a photo is known as the exposure, and it's affected by three things - the shutter speed, the aperture diameter, and the ISO or film speed.
Aperture is measured using the "f-number", sometimes called the "f-stop", which describes the diameter of the aperture. A lower f-number relates to a wider aperture (one that lets in more light), while a higher f-number means a narrower aperture (less light).
Because of the way f-numbers are calculated, a stop doesn't relate to a doubling or halving of the value, but to a multiplying or dividing by 1.41 (the square root of 2). For example, going from f/2.8 to f/4 is a decrease of 1 stop because 4 = 2.8 * 1.41. Changing from f/16 to f/11 is an increase of 1 stop because 11 = 16 / 1.41.
Hence, when the aperture of the camera reduces to half of the original aperture, the exposure time should be half than before.
Question 6
1 / -0

If a star is moving towards earth then the spectrum lines are shifted towards

A
yellow

B
infrared

C
blue

D
green

Solution

Red shift takes place when a star moves away from the earth. Red shift occurs due to Doppler's effect formed in light. The apparent frequency of light is decreased when source is going away from the observer.
Blue shift occurs when the source move towards the observer.
Question 7
1 / -0

Wave front means:

A
all particles in it have same phase

B
few particles are in same phase, rest are in opposite phase

C
all particles have opposite phase of vibrations

D
all particles have random vibrations

Solution

All particles in it have same phase.
It is the imaginary surface representing corresponding points pf a wave that vibrate in unison. When identical waves having a common origin travel through a homogeneous medium , the corresponding crests and troughs at any instant phase.
Question 8
1 / -0

Evidence for the expanding universe is given by _______ of light spectrum received from them.

A
red shift

B
blue shift

C
green shift

D
orange shift

Solution

Red shift
In physics red shift happens when light or other electromagnetic radiation from an object is increased to a wavelength or shifted to the red end of spectrum. A red shift occurs whenever a light source moves away from the observer. A special instance of this in the cosmological red shift, which is due to the expansion of the universe, and sufficiently distant light source shows red shift corresponding to the rate of increase in their distance from earth.
Question 9
1 / -0

By corpuscular theory of light, the phenomenon which can be explained is ____________.

A
refraction

B
diffraction

C
interference

D
polarisation

Solution

Refraction
According to newton, when corpuscles approach the refracting surface , they are attracted near the surface. When they enter the denser medium from a rarer medium, their speed increases and hence change their direction.
Question 10
1 / -0

Which of the following statements about the behaviour of light is not correct?

A
Interference patterns are evident for light behaving as rays.

B
Ray properties of light are useful for understanding how images are formed by optical devices such as eyes.

C
Wave properties are important for observing the behaviour of light at a fine scale.

D
Both wave and particle theories of light can be related to the colour sensations produced by light.

Solution

Interference patterns are explained using wave nature of light. You can learn more from youtube video "Interference of light".