# Class 12th Physics – 10 Wave Optics MCQs

#### When light incident on a transparent interface at polarizing angle the intensity of reflected light is I_{1} and the intensity of refracted light is I_{2}, then ____.

At polarizing angle, the reflected light is completely polarized and contain light with 'E' vector perpendicular to the plane of incidence. But the refracted light contains light that is still not completely polarized. Hence the intensity of refracted light is greater than the intensity reflected light.

#### ' P' is a point in space and S_{1} and S_{2} are two coherent sources generating waves of wavelength 1 cm. If the path difference between S_{1}P and S_{2}P is 5 cm, then waves interfere ____ at P.

Path difference

S_{1}P − S_{2}P = 5 cm

Since wavelength λ = 1 cm

S_{1}P − S_{2}P = 5λ

For path difference equal to integer multiples of wavelength, waves interfere constructively.

#### Interference of waves can be explained with ____.

Interference of waves can be explained with the principle of superposition.

#### In air sound travels with a speed of 340 m/s. The diameter of the spherical sound wave front generated by a point source of sound after 1/10 th of a second is ____

The speed of the wave front in a medium is equal to the speed of the wave in the same medium. That means, the wave front travels at a speed of 340 m/s. In 1/10th of a second, the radius of the spherical wave front becomes "340 × 1/10 = 34 m. The diameter of the wave front after 1/10th of a second must be 68 m.

#### If λ_{1} is the wavelength of light in medium one and λ_{2} is the wavelength of light in medium two, as the wave travels from medium one to medium two, sini/sinr= ____

If λ_{1} is the wavelength of light in medium one and λ_{2} is the wavelength of light in medium two, as the wave travels from medium one to medium two, sini/sinr=λ_{2}/λ_{1 }

#### If the angles made by incident wavefront and reflecting wavefront with the reflecting surface are "θ_{1}" and "θ_{2}", then ____.

The angle, the incident wavefront makes with the reflecting surface is the angle of incidence.

The angle, the reflecting wavefront makes with the reflecting surface is angle of reflection

According to laws of reflection θ_{1} = θ_{2}.

#### If v_{1} and v_{2} are the speeds of a wave in two different media of refractive indices n_{1} and n_{2} respectively and n_{1} < n_{2}, then ____

If v_{1} and v_{2} are the speeds of a wave in two different media of refractive indices n_{1} and n_{2} respectively and n_{1} < n_{2}, then v_{1} >v_{2}

#### If at a point "P" interfering waves from two coherent sources are differing in phase by 7π4, then at "P" ____.

The phase difference in the given case = 7π4

The general expression for constructive interference is phase difference = 2nπ

The general expression for destructive interference is phase difference = (2n + 1)π

Since the given phase difference is not in any of these forms, there will be no interference at "P".

#### When a slit is illuminated with a light of wavelength 6000A, the first minima is obtained at θ = 20° the slit width is ____.

The angular position of the first minima is given by

θ=λ/a

⇒a=λ/θ

=(6000×10^{−10}/20×2π)×360

=6000×10^{10}×360×7/20×2×22

= 17.2 × 10^{−4} mm
θ=λ/a

⇒a=λ/θ

=(6000×10^{−10}/20×2π)×360

=6000×10^{10}×360×7/20×2×22

= 17.2 × 10^{−4} mm

#### According to Huygens, the amplitude of secondary wavelets is ___ in the forward direction and ____ in the backward direction.

According to Huygens, the amplitude of secondary wavelets is maximum in the forward direction and zero in the backward direction.

#### a) Primary waves can travel in all directions in a given medium. b) Secondary waves can travel only in the forward direction but not in backward direction

Primary waves can travel in all directions in a given medium. Secondary waves can travel only in the forward direction but not in backward direction.

#### When waves from two coherent sources, each producing waves of intensity Io, interfere constructively at 'P' and destructively at 'Q', then the intensity of waves at 'P' is ____ and at Q is ____.

When two waves interfere constructively, the intensity becomes four times the intensity of each wave. When they interfere destructively, the intensity becomes zero.

#### In a medium, the speed of the wave front is ____ the speed of the wave in that medium.

In a medium, the speed of the wave front is equal to the speed of the wave in that medium.

#### Wave front is an imaginary surface representing locus of points oscillating ____.

Wave front is an imaginary surface representing locus of points oscillating in phase

#### Huygens principle is used to ____

Huygens principle is used to determine the shape and position of the wave front at a later time.

#### Huygens' Principle is applicable ____

Huygens' principle is useful for all types of waves.

#### A plane wave front, after travelling for a long time, will behave like a ____

A plane wave front, after travelling for a long time, will behave like a plane wave front only

#### When unpolarised light incident at Brewster's angle, the reflected light is polarized with its ____ to the plane of incidence.

When unpolarised light incident at Brewster's angle, the reflected light is completely polarized with its electric vector perpendicular to the plane of incidence.

#### If 'θ' is the angle an incident wave front makes with the refracting surface, then the angle of incidence is ____

If 'θ' is the angle an incident wavefront makes with the refracting surface, then the angle of incidence is 'θ'.

#### The refractive index of a material is equal to the tangent of the polarizing angle. This is known as ____.

According to Brewster's law, the refractive index of a material is equal to the tangent of the polarizing angle.

#### The angular width of central maxima in Fraunhoffer diffraction when light of wavelength 5500A is used and the slit width is 11 × 10^{−5} cm

θ=2λ/a

=2×5500×10^{−10}/11×10^{−5}×10^{−2}

= 1 rad

#### As a wave propagates from one refractive medium to another, there will be no change in ____ of the wave.

As a wave propagates from one refractive medium to another, there will be no change in frequency of the wave.

#### Light exhibits polarization because ____.

Polarization is a phenomenon exhibited by all transverse waves. Since light waves are transverse in nature, they also exhibit polarization.

#### When a wave is passing from a denser medium to rarer medium an angle of incidence of 0^{0}0^{0}, then after refraction, ____

When a wave is passing from a denser medium to rarer medium an angle of incidence of 0^{0}, then after refraction, waves travel without bending.

#### In which of the following Polaroids are not used.

Polaroids are used to control the intensity of light. In case of telescopes, no such Polaroid is required.

#### When unpolarized light incident on the boundary between two transparent media and if the reflected wave is perpendicular to the refracted wave, then ___

When the reflected and refracted waves are perpendicular to each other, the reflected wave is completely polarized. This is the condition of Brewster's law.

#### The shape of the wave fronts formed on the surface of water is ____

The shape of the wave fronts formed on the surface of water is circular.

#### a) Each point of the primary wave acts as a source of a secondary disturbance b) Common tangent to all secondary wavelets gives the new position of the wave

According to Huygens principle, each point of the primary wave acts as a source of a secondary disturbance and the common tangent to all secondary wavelets gives the new position of the wave.

#### Two sources are said to be coherent if ____.

Two sources are said to be coherent if frequency of waves produced is same for both and the phase difference between the displacements produced by each of the waves does not change.

#### Speed of light in a medium of refractive index n1 is 2.5 × 10^{8} m/s and in another medium of refractive index n2 is 2 × 10^{8} m/s, then ____

Since speed of light is less in a medium of high refractive index,
n_{2} > n_{1}

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