The Photon, the Quantum of Light MCQ Quiz in मल्याळम - Objective Question with Answer for The Photon, the Quantum of Light - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

A quantum is defined as the minimum amount of any physical entity involved in an interaction. For example, a photon is a single quantum of light.

Photon: 

1) A photon is a tiny light particle that comprises waves of electromagnetic radiation.

2) James Maxwell observed photons are just electric fields traveling through space.

3) Photons have no charge and no resting mass.

4) It travels at the speed of light. 

The energy of Photon is given by:

E = hν

Where,

h is Planck's constant, and

ν is the frequency of the Electromagnetic wave associated with the photon

h = 6.626 070 15 x 10-34 J Hz-1  

Additional Information

Positrons:

• Positron, also called positive electron, positively charged subatomic particle having the same mass and magnitude of charge as the electron and constituting the antiparticle of a negative electron.
• The first of the antiparticles to be detected, positrons were discovered by Carl David Anderson.

Phonons:

• The thermal vibrations resulting from the thermal energy of the substances are called phonons.
• They can't absorb or emit electromagnetic radiation. 

Optical phonons:

• The quantum of the lattice vibration in opposite directions are called optical phonons.
• The optical phonons are observed for the crystals containing multiple atoms as a basis such as NaCl, GaAs, ZnO, etc.

Phantom Loading:

• It is the phenomenon in which the appliances consume electricity even when they turn off.
• The phantom loading is used for examining the current rating ability of the energy meter.
• The actual loading arrangement will waste a lot of power.
• The phantom loading consumes very less power as compared to real loading, and because of this reason, it is used for testing the meter.

CONCEPT:

• The wavelength of the electron due to its motion is called the de-Broglie wavelength of the electron.
• The bundle of light rays is called a photon.
• The de-Broglie wavelength of an electron (λe) is given by:

\({λ _e} = \frac{h}{mv}\)

• Energy of a photon (E) = (hc)/λ

∴ The wavelength of the photon is

\(⇒ λ =\frac{{h\;c}}{E}\)

Where E = energy, h = Planck constant, m = mass of electron and c = speed of light

EXPLANATION:

Given - velocity of electron (v) = 500km/s = 5 × 10⁵ m/s

The wavelength of an electron moving with a velocity of 500km/s is 

\(\Rightarrow {λ _e} = \frac{6.64\times10^{-34} }{9.1\times 10^{-31}\times 5\times 10^5}=0.145\times 10^8=1.45 \,nm\)

CONCEPT:

EXPLANATION:

• In the photoelectric experiment, light behaves as a particle.
• When light undergoes diffraction and refraction it behaves as a wave. Hence, diffraction and refraction indicate that light is a wave. Therefore, option 1 is correct. 

CONCEPT:

• Light shows dual nature: Some phenomena can be explained by the wave nature of light while some by the quantum nature of light.
• Wave nature of light: James Clerk Maxwell showed that light is an electromagnetic wave that travels at the speed of light through space. Diffraction, interference, and polarization are some phenomena that can be explained by the wave nature of light.
• Quantum nature of light: Light consists of photons or quanta of energy that gives particle nature to it. The Photoelectric effect can be explained by the quantum nature of light.

EXPLANATION:

Photoelectric effect: 

• The emission of free electrons from a metal surface when the light is shone on it, it is called the photoemission or the photoelectric effect. 
• This effect led to the conclusion that light is made up of packets or quantum of energy.

Interference: 

• When two light waves of the same frequency having a zero or constant phase difference propagate in a medium simultaneously in the same direction, then due to their superposition maximum intensity is obtained at few points and minimum intensity at other few points. It is called interference of light.

Diffraction: 

• Diffraction is the bending of light at the sharp ends of the obstacles or holes. It can be explained by the wave nature of light.

Polarization: 

• Polarization, in Physics, is defined as a phenomenon caused due to the wave nature of electromagnetic radiation.
• When a light ray is passed through a special crystal then its vibrations only in a plane perpendicular to the direction of propagation remain, it is called the polarization of light.
• Hence, option 1 is correct.

CONCEPT:

Light shows dual nature:

• Some phenomena can be explained by the wave nature of light while some by the quantum nature of light.

EXPLANATION:

Photoelectric effect: 

• The emission of free electrons from a metal surface when the light is illuminated on it, it is called the photoemission or the photoelectric effect. 
• This effect led to the conclusion that light is made up of packets or quantum of energy. Hence, option 4 is correct.

CONCEPT:

Quantum nature of light:

• Light consists of photons or quanta of energy that gives particle nature to it.
• The Photoelectric effect can be explained by the quantum nature of light.

Photon:

• According to Einstein's theory, the light propagates in the bundles of energy, each bundle is being called a photon.
• The energy of a photon is given as,

⇒ E = hν

• ​The rest mass of the photon is zero. But its effective mass is given as, 

\(\Rightarrow m=\frac{h}{cλ}\)

Where h = Planck's constant, c = speed of light, λ = wavelength and ν = frequency

• Photon exerts pressure on the surface.

EXPLANATION:

• From the above explanation, it is clear that,
  • The rest mass of the photon is zero.

  • The energy of the photon is hν.

  • Photon exerts pressure on the surface.

• Hence, option 2 is correct.

The correct answer is option 1) i.e. 3 × 1016.

CONCEPT:

The energy of a photon:

• Photons have wave-like and particle-like properties. Light is a form of energy and this energy comes from the energy of the photons that constitute light. 
• Photon is a bundle of electromagnetic energy. The energy of a photon is given by:

 \(E =\frac{hc}{λ}\)

Where E is the energy of a single photon, c is the speed of light in a vacuum, and λ is the wavelength of a given light.

Power is defined as the amount of work done on an object or work done by an object per unit of time.

Work done is nothing but the energy lost/gained by an object.

∴ Power = \(\frac{Total\:energy} {time}\) 

CALCULATION:

Given that:

Wavelength of light, λ = 667 nm = 667 × 10^-9 m

Power emitted = 9 mW = 9 × 10^-3 W

Energy for a single photon, \(E =\frac{hc}{λ}\)

= \(\frac{6.626 × 10^{-34} × (3 × 10^8)}{667 × 10^{-9}}\) = 2.97 ×  10^-19 J

The power emitted for the given light stands for the power due to 'n' number of photons of the light.

Power = \(\frac{ Energy \:of\: single\: photon × n}{time}\)

9 × 10-3 = \(\frac{ 2.97 × 10^{-19} × n}{1}\)       

(∵ number of photons arriving per second ⇒ time = 1 s)

n = \(\frac{9 \times 10^{-3}}{2.97 \times 10^{-19}}\)= 3 × 1016 photons

Concept:

• Quantum Theory was propounded by physicist Max Planck in 1900 when he made an assumption that the energy was made of ‘quanta’ or individual units.
• The theory explains the behaviour and nature of energy and matter on the atomic and subatomic level.
• This nature is also referred to as quantum mechanics or quantum physics.
• Later, in 1905, Albert Einstein theorized that radiation itself was quantized and not just the energy.

Explanation:

• Whereas, According to Planck’s quantum theory, the energy of light is proportional to its frequency and also that light exists in discrete quanta of energy.
• The light according to it is in the form of discrete packets of energy.
• Max Planck gave an explanation to this observation by his Quantum Theory of Radiation.

His theory says: The Radiant energy is always in the form of tiny bundles of light called quanta i.e. the energy is absorbed or emitted discontinuously.

• The value of Planck’s constant is 6.626 × 10-34 J.s. It is denoted by h and comes into play in the relation Energy, E = hν
• Planck’s constant \(h = \frac{{Energy\;of\;photon\;\left( E \right)}}{{frequency\;of\;photon\;\left( f \right)}} \Rightarrow \frac{{\left[ {{M^1}{L^2}{T^{ - 2}}} \right]}}{{\left[ {{T^{ - 1}}} \right]}} = \left[ {{M^1}{L^2}{T^{ - 1}}} \right]\)
• Its unit of J.s, Energy is represented as Joules and time as sec.

CONCEPT:

• A perfect black body absorbs all the electromagnetic radiation incident on it.
• The black body radiation spectrum is the spectrum of radiation emitted by a black body when it is at a higher temperature than its surroundings.
• Stefan-Boltzmann's law states that the total power radiated per unit surface area of a black body is proportional to the fourth power of the temperature of the black body. 

⇒ P ∝ T⁴

⇒ P = kT⁴ 

• In the above equation, T is the temperature of the black body in Kelvin, k is the proportionality constant and P is the power radiated per unit surface area of a black body in J/(s.m²).

CALCULATION:

Given - P₁ = 1.0 × 105 Joule per sec. per m2, P2 = 81 × 105 Joule/sec/m2, and T₁ = 500 K

Case 1:

\(\Rightarrow P_1=kT^4_1\)

\(⇒ k=\frac{P}{T^4} =\frac{1.0 \times 10^5}{500^4}=1.6\times 10^{-6} \frac{J}{s.m^2.K^4 }\)

Case 2: 

\(\Rightarrow P_2=kT^4_2\)

\( ⇒ T^4_2=\frac{P_2}{k} =\frac{81.0 \times 10^5}{1.6\times 10^{-6}}=5.0625\times 10^{12} K^4 \\ ⇒ T_2 = 1500 K\)

• Therefore, option 3 is correct. 

Additional Information

• For a perfect black body with emissivity ϵ = 1, the value of Stefan-Boltzmann's constant is \(σ = \frac{P}{T^4} = 5.67 \times 10^{-8} \frac{J}{s.m^2.K^4}\). 
• For a non-perfect black body with emissivity ϵ < 1, the Stefan-Boltzmann's law modifies as P = ϵσT4 or P = kT4.

The correct answer is option 3) i.e. Photon has a fixed mass.

CONCEPT:

• Photon: Photon is the elementary unit that makes up light. It is the discrete amount of electromagnetic energy. 
• The properties of a photon are: 
  1. It has no mass.
  2. It does not have any electrical charge.
  3. It can be created or destroyed only when radiation is emitted or absorbed.
  4. It is not affected by the magnetic field and electric field.
  5. A photon travels with a speed = 3 x 108 m/s.

​EXPLANATION:

• Photon is massless and therefore, option 3) is the incorrect statement.