Physics: CUET Mock Test - 7 - CUET MCQ

The process in which an electron escapes from the metal surface is known as electron emission. Electrons are loosely bound to the nucleus, and therefore, a little energy push sets these electrons flying out of their respective orbits.

There are four types of electron emissions, namely, thermionic emission, photoelectric emission, secondary emission, and field emission. These are the different methods of producing electron emissions.

Only transverse waves show the property of polarization. Their vibrations can occur in all directions perpendicular to the direction of travel. The longitudinal, infrared, and microwaves do not show the property of polarization.

tan i_p = μ = √3.
i_p = tan^-1(√3)
i_p = 60^o
Therefore, the polarization angle of a medium of refractive index √3 is 60^o.

An electric field vector is used to represent the polarization of an em wave. It is perpendicular to the plane of propagation of the light wave. Therefore, a vertically polarized electromagnetic wave of wavelength λ has its electric field vector oscillating in the vertical direction.

Plane of vibration, the plane of polarization, and direction of propagation of the light wave are mutually perpendicular to the polarized light wave in a plane. The other factors are not mutually perpendicular to the polarized light wave in a plane.

The plane containing the direction of propagation of light and perpendicular to the plane of vibration is called the plane of polarization. It contains no vibrations. Polarized light waves are light waves in which the vibrations occur in a single plane.

Polaroids absorb only that part of the light which produces a dazzling effect in the eye. But colored glasses absorb more light incident on them and so the image appears dim. Therefore, sunglasses are made of Polaroids.

As i_p + r_p = 90^o
r_p = 90^o – 63.8^o
r_p = 26.2^o
Therefore, the angle of refraction in the glass is 26.2^o.

Coherent light is a form of light whose photons share the same frequency and whose wavelengths are in phase with one another. The phase difference between the waves should be constant in case of coherent sources.

LED is the odd one out. LED is short for light-emitting diode. LED is not a coherent source, whereas, others are examples of coherent sources. The light emitted from an LED is neither spectrally coherent nor even highly monochromatic.

Coherent waves are the waves with the same frequency and the wavelength of the waves are in phase as well. Therefore, the phase difference is constant. But the coherent waves do not have the same amplitude. Since the amplitude is different, there will be no complete constructive interference where they meet, so they will contribute poorly to an interference pattern.

Coherence length is defined as the propagation distance over which a coherent wave maintains a specified degree of coherence. Wave interference is strong when the paths taken by all of the interfering waves are lesser than the coherence length.

The formula for calculating coherence time is given as:

Where Τ_c is the coherence time, λ is the wavelength, ∆λ is the spectral width of the source, and c is the speed of light in a vacuum (i.e. 3 × 10⁸ m/s).

LASER is the short form for Laser Amplification by Stimulated Emission Radiation. The amplified light beam coming out of a LASER is essentially due to the emission of electrons stimulated by incident radiation consisting of photons. As a result, this causes the coherent behavior of the LASER beam.

Light of shorter wavelengths is scattered much more than light of longer wavelengths. The amount of scattering is inversely proportional to the fourth power of the wavelength. This is known as Rayleigh scattering.

Generally, there are two kinds of rainbows, namely primary rainbow and secondary rainbow. The primary rainbow occurs due to one internal reflection and two refractions, whereas secondary rainbow occurs due to two internal reflections and two refractions, from the water drops suspended in the air.

During sunrise and sunset, the rays have to travel a large part of the atmosphere since the rays are close to the horizon at that time. That is why, red being the least scattered enters our eyes, as all the other colors get scattered away.

A rainbow is an example of a dispersion of sunlight by the water drops in the atmosphere. This is a phenomenon due to the combined effect of dispersion, refraction, and reflection of sunlight by spherical water droplets of rain. Others all are common illustrations of scattering of light.

A prism is a homogenous, transparent medium enclosed two plane surfaces inclined at an angle. These surfaces are called the refracting surfaces and the angle between the incident ray and emergent ray is known as the angle of deviation.

Cauchy’s dispersion formula is an empirical expression that gives an approximate relation between the refractive index of a medium and the wavelength of the light. Cauchy’s formula is given as:

Where A, B, and C are the arbitrary constants of the medium.

The difference in a deviation between any two colors is known as angular dispersion. Angular dispersion is given as:
δ_V - δ_R = (μ_V - μ_R)A
Where μ_V and μ_R are the refractive index for violet rays and red rays, respectively. Mean deviation is .

Consider combining two prisms of refracting angles A and A’, and dispersive powers ω and ω’ respectively in such a way that their refracting angles are reversed concerning each other. For no deviation, the condition is:
δ + δ’ = 0
So, (μ - 1)A + (μ’ - 1)A’ = 0 or 

Given: The refractive index for violet color = 1.456; Refractive index for red color = 1.414
Required equation

ω = 0.096
Therefore, the dispersive power of crown glass is 0.096.

The required equation
⇒ δ = (μ - 1)A
When two prisms are combined, then:
δ = δ + δ’ = (μ - 1)A + (μ’ - 1)A’ = 0

Therefore, the angle of the other prism is 1^o and opposite of the first prism.

The formula for dispersive power is given as:
Dispersive power (ω) = 

Where  = mean refractive index

The classification of electromagnetic waves done according to the frequency called the electromagnetic spectrum. The basic difference various type of electromagnetic waves lies in their wavelength or frequency since all of them travel through vacuum at the same speed and also, the waves differ in their mode of interaction with matter.

UHF stands for Ultra high frequency. Cellular phones used radio waves to transmit voice communication in the Ultra high-frequency Band. The UHF band extends from 900 MHz to 5 x 109 Hz or 5000 MHz. Radio waves are produced by oscillating circuits having an inductor and capacitor.

Microwave ovens are an application of microwaves. In microwave ovens, the frequency of microwave produced is matched with the natural frequency of water molecules so that resonance occurs and water molecules in the material vibrate at the higher amplitude and transfer energy to nearby food molecules, results in heating the food.

Ultraviolet (UV) radiations in large quantities are highly harmful to humans. These rays in solar radiation on reaching earth are absorbed by the ozone layer in the atmosphere. UV rays are produced by special lamps such as mercury and from arc lamps and by very hot bodies like the sun.