# MCQ Questions Chapter 8 Electromagnetic Waves Class 12 Physics

Please refer to MCQ Questions Chapter 8 Electromagnetic Waves Class 12 Physics with answers provided below. These multiple-choice questions have been developed based on the latest NCERT book for class 12 Physics issued for the current academic year. We have provided MCQ Questions for Class 12 Physics for all chapters on our website. Students should learn the objective based questions for Chapter 8 Electromagnetic Waves in Class 12 Physics provided below to get more marks in exams.

## Chapter 8 Electromagnetic Waves MCQ Questions

Please refer to the following Chapter 8 Electromagnetic Waves MCQ Questions Class 12 Physics with solutions for all important topics in the chapter.

MCQ Questions Answers for Chapter 8 Electromagnetic Waves Class 12 Physics

Question. A linearly polarized electromagnetic wave given as E = E0 i cos (kz–ωt) is incident normally on a perfectly reflecting infinite wall at z = a. Assuming that the material of the wall is optically inactive, the reflected wave will be given as

B

Question. The electric field intensity produced by the radiations coming from 100 W bulb at a 3 m distance is E0. The electric field intensity produced by the radiations coming from 50 W bulb at the same distance is
(A) E0/2
(B) 2E0
(C) E/√2
(D) √2E

C

Question. If E and B→ represent electric and magnetic field vectors of the electromagnetic wave, the direction of propagation of electromagnetic wave is along
(A) E B
(B) B  ⊥ E→
(C) B × E
(D) E × B

D

Question. In electromagnetic waves, the phase difference between magnetic and electric field vectors is
(A) zero
(B) π
(C) π/2
(D) π/4

A

Question. The ratio of contributions made by the electric field and magnetic field components to the intensity of an EM wave is
(A) c : 1
(B) c2 : 1
(C) 1 : 1
(D) √c :1

C

Question. An EM wave radiates outwards from a dipole antenna, with E0 as the amplitude of its electric field vector. The electric field E0 which transports significant energy from the source falls off as
(A) 1/r3
(B) 1/r2
(C) 1/r
(D) remains constant

C

Question. From Maxwell’s hypothesis, a changing electric field gives rise to
(A) an electric field
(B) an induced emf
(C) a magnetic field
(D) a magnetic torque

C

Question. In vacuum, the wavelength of the electromagnetic wave of frequency 5 × 1019 Hz is
(A) 6 × 10–12 m
(B) 3 × 10–8 m
(C) 1.6 × 1011 m
(D) 15 × 1027 m

A

Question. Light with an energy flux of 20 W/cm2 falls on a non-reflecting surface at normal incidence. If the surface has an area of 30 cm2, the total momentum delivered (for complete absorption) during 30 minutes is
(A) 36 × 10–5 kg m/s
(B) 36 × 10–4 kg m/s
(C) 108 × 104 kg m/s
(D) 1.08 × 107 kg m/s

B

Question. The electromagnetic radiations used for water purification and eye surgery is
(A) Infrared
(B) Microwave
(C) X-rays
(D) None of the above

D

Question. One requires 11 eV of energy to dissociate a carbon monoxide molecule into carbon and oxygen atoms. The minimum frequency of the appropriate electromagnetic radiation to achieve the dissociation lies in
(A) visible region
(B) infrared region
(C) ultraviolet region
(D) microwave region

C

Question. Electromagnetic wave having frequency 5 × 1011 Hz is
(A) Ultraviolet wave
(C) Microwave
(D) X-rays

C

Question. Which one of the following statements are correct?
(B) Water molecules readily absorb infrared radiation and their thermal motion increases.
(C) Microwaves are produced in Coolidge tube.
(D) Gamma radiations generate due to electron transitions between upper and lower energy levels of heavy element when excited by electron bombardment.

B

Question. Proper arrangement of Gamma rays, Microwave, IR wave and UV rays in ascending order of frequency is
(A) Gamma rays > UV rays > IR rays > Microwave
(B) Microwave > IR rays > UV rays > Gamma rays
(C) UV rays > Gamma rays > Microwave > IR rays
(D) IR rays > UV rays > Microwave > Gamma rays

A

Question. The phenomenon which shows quantum nature of electromagnetic radiation is
(A) Piezoelectric effect
(B) Photoelectric effect
(C) Hall effect
(D) Tyndall effect

B

Question. In vacuum, the physical property which remains same for microwave of wavelength 1 mm and UV radiation 1600 Å is
(A) Wavelength
(B) Frequency
(C) Speed
(D) None of the above

C

Assertion and Reason Based MCQs

Directions: In the following questions, a statement of
Assertion (A) is followed by a statement of Reason (R).
Mark the correct choice as:
(A) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(B) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(C) (A) is true, but (R) is false.
(D) (A) is false, but (R) is true.

Question. Assertion (A): Electromagnetic radiation exerts pressure.
Reason (R): Electromagnetic waves carry momentum and energy.

B

Question. Assertion(A): The Ozone layer present at the top of stratosphere is very crucial for human survival.
Reason (R): Ozone layer prevents IR radiation.

C

Question. Assertion (A): Electromagnetic wave does not require any medium to travel.
Reason (R): Electromagnetic wave cannot travel through any medium.

C

Question. Assertion (A): X-ray travels with the speed of light.
Reason (R): X-ray is an e.m. wave.

A

Question. Assertion (A): Gamma rays are electromagnetic waves having the smallest wavelength.
Reason (R): Gamma rays are having the lowest frequency.

C

Question. Assertion (A): Microwaves are considered suitable for radar system.
Reason (R): Microwaves are of shorter wavelength.

A

Question. Assertion (A): Dipole oscillation produce electromagnetic waves.
Reason (R): Accelerated charge produce electromagnetic waves.

A

Case-based MCQs

I. Read the following text and answer the following questions on the basis of the same:
Microwave oven:
The spectrum of electromagnetic radiation contains a part known as microwaves. These waves have frequency and energy smaller than visible light and wavelength larger than it. What is the principle of a microwave oven and how does it work ? Our objective is to cook food or warm it up. All food items such as fruit, vegetables, meat, cereals, etc., contain water as a constituent. Now, what does it mean when we say that a certain object has become warmer? When the temperature of a body rises, the energy of the random motion of atoms and molecules increases and the molecules travel or vibrate or rotate with higher energies. The frequency of rotation of water molecules is about 2.45 gigahertz (GHz). If water receives microwaves of this frequency, its molecules absorb this radiation, which is equivalent to heating up water. These molecules share this energy with neighbouring food molecules, heating up the food. One should use porcelain vessels and non metal containers in a microwave oven because of the danger of getting a shock from accumulated electric charges. Metals may also melt from heating. The porcelain container remains unaffected and cool, because its large molecules vibrate and rotate with much smaller frequencies, and thus cannot absorb microwaves. Hence, they do not get eaten up. Thus, the basic principle of a microwave oven is to generate microwave radiation of appropriate frequency in the working space of the oven where we keep food. This way energy is not wasted in heating up the vessel. In the conventional heating method, the vessel on the burner gets heated first and then the food inside gets heated because of transfer of energy from the vessel. In the microwave oven, on the other hand, energy is directly delivered to water molecules which is shared by the entire food.

Question. Why should one use porcelain vessels and nonmetal containers in a microwave oven ?
(A) Because it will get too much hot.
(B) Because it may crack due to high frequency.
(C) Because it will prevent the food items to become hot.
(D) Because of the danger of getting a shock from accumulated electric charges.

D

Question. When the temperature of a body rises:
(A) the energy of the random motion of atoms and molecules increases.
(B) the energy of the random motion of atoms and molecules decreases.
(C) the energy of the random motion of atoms and molecules remains same.
(D) the random motion of atoms and molecules becomes streamlined.

A

Question. In the microwave oven,
(A) energy is directly delivered to water molecules which is shared by the entire food.
(B) the vessel gets heated first, and then the food grains inside.
(C) the vessel gets heated first and then the water molecules collect heat from the body of the vessel.
(D) energy is directly delivered to the food grains.

A

Question. As compared to visible light microwave has frequency and energy:
(A) more than visible light.
(B) less than visible light.
(C) equal to visible light.
(D) Frequency is less but energy is more.

B

Question. The frequency of rotation of water molecules is about:
(A) 2.45 MHz.
(B) 2.45 kHz.
(C) 2.45 GHz.
(D) 2.45 THz.

C

II. Read the following text and answer the following questions on the basis of the same:
Laser:
Electromagnetic radiation is a natural phenomenon found in almost all areas of daily life, from radio waves to sunlight to x-rays. Laser radiation – like all light – is also a form of electromagnetic radiation. Electromagnetic radiation that has a wavelength between 380 nm and 780 nm is visible to the human eye and is commonly referred to as light. At wavelengths longer than 780 nm, optical radiation is termed infrared (IR) and is invisible to the eye. At wavelengths shorter than 380 nm, optical radiation is termed ultraviolet (UV) and is also invisible to the eye. The term “laser light” refers to a much broader range of the electromagnetic spectrum that just the visible spectrum, anything between 150 nm up to 11000 nm (i.e. from the UV up to the far IR). The term laser is an acronym which stands for “light amplification by stimulated emission of radiation”.
Einstein explained the stimulated emission. In an atom, electron may move to higher energy level by absorbing a photon. When the electron comes back to the lower energy level it releases the same photon. This is called spontaneous emission. This may also so happen that the excited electron absorbs another photon , releases two photons and returns to the lower energy state. This is known as stimulated emission.
Laser emission is therefore a light emission whose energy is used, in lithotripsy, for targeting and ablating the stone inside human body organ. Apart from medical usage, laser is used for optical disk drive, printer, barcode reader etc.

Question. LASER is used in:
(A) optical disk drive.
(B) transmitting satellite signal.
(D) ionization.

A

Question. What is the range of amplitude of LASER?
(A) 150 nm – 400 nm
(B) 700 nm – 11000 nm
(C) Both the above
(D) None of the above

C

Question. What is the full form of LASER ?
(A) Light amplified by stimulated emission of radiation
(B) Light amplification by stimulated emission of radiation
(C) Light amplification by simultaneous emission of radiation
(D) Light amplified by synchronous emission of radiation

B

Question. Lithotripsy is:
(A) an industrial application.
(B) a medical application.
(C) laboratory application.
(D) process control application.

B

Question. The “stimulated emission” is the process of :
(A) release of a photon when electron comes back from higher to lower energy level.
(B) release of two photons by absorbing one photon when electron comes back from higher to lower energy level.
(C) absorption of a photon when electron moves from lower to higher energy level.
(D) None of the above

B

III. Read the following text and answer the following questions on the basis of the same:
Ozone layer depletion:
We are all exposed to UV radiation from the sun. The sun is by far the strongest source of ultraviolet radiation. UV radiation spectrum is divided into three regions called UVA, UVB and UVC. As sunlight passes through the atmosphere, all UVC and most UVB is absorbed by ozone, water vapour, oxygen and carbon dioxide. UVA is not filtered as significantly by the atmosphere.
The three types of UV radiation are classified according to their wavelength. They differ in their biological activity and the extent to which they can penetrate the skin. The shorter the wavelength, the more harmful the UV radiation.
The UV region covers the wavelength range 100-400 nm and is divided into three bands:
• UVA (315-400 nm)
• UVB (280-315 nm)
• UVC (100-280 nm).
Short-wavelength UVC is the most damaging type of UV radiation. However, it is completely filtered by the atmosphere and does not reach the earth’s surface.
UV level reaching the earth changes with latitude and altitude.
UV levels are higher closer to the equator. Closer to the equator the sun’s rays have a shorter distance to travel through the atmosphere and therefore harmful UV radiation absorption is less.
With increasing altitude less atmosphere is available to absorb UV radiation. With every 1000 m in altitude, UV levels increase by approximately 10%.
Ozone is a particularly effective absorber of UV radiation. As the ozone layer gets thinner, the protective filter activity is progressively reduced. Consequently, the people and the environment are exposed to higher levels of UV radiation, especially UVB.
Ozone depletion is caused by human-made chemicals released into the atmosphere.

Question. Ozone layer depletion is caused by
(A) cosmic rays
(B) human-made chemicals released into the atmosphere
(C) electrical spark in the atmosphere
(D) None of the above

B

Question. Most harmful UV radiation band is
(A) UVA
(B) UVB
(C) UVC
(D) all of them

C

Question. UV level is
(A) low at equator, high at poles.
(B) low at poles, high at equator.
(C) same at pole and equator.
(D) None of the above

B

Question. How many bands are there in UV radiation spectrum?
(A) 2
(B) 5
(C) 3
(D) 4

C

Question. Which UV band is not absorbed by the atmosphere?
(A) UVA
(B) UVB
(C) UVC
(D) none of them

A

Assertion-Reason Questions

In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R). Choose the correct answer out of the following choices.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.

Question. Assertion (A): The speed of electromagnetic waves in free space is maximum for gamma rays and minimum for radio waves.
Reason (R): For waves with same wavelengths this just means that the speed will be equal to c.

D

Question. Assertion (A): If earth’s atmosphere disappears the average surface temperature will increase.
Reason (R): Without an atmosphere to trap Earth’s heat, the temperature will increase.

D

Question. Assertion (A): If a beam of polarised light passes through a polaroid with polarization angle θ to the axis of polarization of the sheet, the intensity of transmitted light is I = I0 cos2θ.
Reason (R): In the situation described above, electric field amplitude is given by E=E0 cosθ.

A

Question. Assertion (A): In an electromagnetic wave, electric field vector and magnetic field vector are mutually perpendicular.
Reason (R): Electromagnetic waves are transverse.

B

Question. Assertion (A): Short wave band is used for transmission of radiowaves to large distances.
Reason (R): Short waves are reflected by earth’s ionosphere.

A

Question. Assertion (A): Microwaves are better carriers of signals than optical waves.
Reason (R): Microwaves move faster than optical waves.

C

Question. Assertion (A): Gamma rays are more energetic than X-rays.
Reason (R): Gamma rays are of nuclear origin while X-rays originate from heavy atoms.

A

Question. Assertion (A): In an electromagnetic wave electric and magnetic field vectors are mutually perpendicular and have a phase of π/2.
Reason (R): Phase difference refers to time difference. There is a time difference between the peaks of electric and magnetic oscillations in EM waves.

D

Question. Assertion (A): Electromagnetic wave is produced by accelerated charge.
Reason (R): An accelerated charge produces both electric and magnetic fields and also radiates them.