Characteristics of EM Waves Questions

---

Very Short Answers Questions [1 Mark Questions]

Ques. Which basic oscillatory circuit is used these days to produce electromagnetic waves?

1. LCR circuit
2. Capacitive circuit
3. LC oscillatory circuit
4. Inductive circuit

Ans. The correct answer is c. LC oscillatory circuit

Explanation: Nowadays, electromagnetic waves are produced using an LC oscillatory circuit. It produces electromagnetic waves of frequency f = 1/2π√LC.

Ques. If the wavelength of electromagnetic radiation is doubled, what will happen to the energy of photons?

1. Halved
2. Becomes zero
3. Remains the same
4. Doubled

Ans. The correct answer is a. Halved

Explanation: The energy of a photon is inversely proportional to the wavelength. Therefore, if the wavelength of electromagnetic radiation is doubled, then the energy of photons becomes halved.

Ques. Is the ratio of frequencies of UV rays and IR rays in the glass more than, less than, or equal to 1?

1. More than 1
2. Equal to 1
3. Less than 1
4. Insufficient data

Ans. The correct answer is a. More than 1

Explanation: The frequency ratio of UV and IR rays in the glass is more than one. This is due to the fact that UV rays have a higher frequency than infrared radiation. This condition can occur in glass, vacuum, or air.

Ques. Microwaves can’t be used for long-distance transmission of signals.

1. True
2. False

Ans. The correct answer is a. False

Explanation: Microwaves are not bent by objects of normal dimensions due to their shorter wavelength. So, they may be utilized to direct a signal in a certain direction. Therefore, microwaves may be used for long-distance signal transmission.

Ques. What is the ratio of the speed of infrared and ultraviolet rays in a vacuum?

1. 0
2. 1
3. 1:5
4. 2:1

Ans. The correct answer is b. 1

Explanation: Because the speed of an electromagnetic wave in a vacuum is independent of its wavelength or frequency, the ratio of speed of infrared and ultraviolet radiation in a vacuum equals one.

---

Short Answers Questions [2 Marks Questions]

Ques. What are Electromagnetic Waves?

Ans. When an electric field interacts with a magnetic field, electromagnetic waves are formed, which are also referred to as EM waves. Electromagnetic waves consist of electromagnetic radiation. The production of electromagnetic waves is due to oscillating electric and magnetic fields.

Ques. Write any 2 applications of Infrared radiations.

Ans. Infrared radiation applications include-

• Infrared radiation is useful for photographing in cloudy conditions.
• In spectroscopy and astronomy, infrared radiations are also used.

Ques. Name the property of an electromagnetic wave that is dependent on the medium in which it is traveling.

Ans. The velocity of an electromagnetic wave is a property that depends on the medium through which it travels. Other qualities, like as frequency, time period, and wavelength, are determined by the source of the wave.

Ques. What is ground wave propagation?

Ans. Ground wave propagation, also known as surface wave propagation is a type of radio propagation that propagates waves over the surface of the earth in low and medium frequencies. They are mainly used for communication between the surface of the earth and the ionosphere.

Also check: 

---

Long Answers Questions [3 Marks Questions]

Ques. What are the applications of electromagnetic waves?

Ans. The following are the applications of electromagnetic waves

• EM radiation helps in transporting energy in a vacuum or no medium at all.
• EM waves are essential in communication technologies.
• RADARS uses EM waves.
• UV rays are quite useful in identifying fake banknotes.
• Infrared radiation has applications in security cameras and for night vision.

Ques. Explain the formation of EM waves.

Ans. When a charged particle generates an electric field, the field exerts force on other particles, resulting in negative and positive charges. 

• When these charges are accelerated, positive charges tend to travel in the direction of the electric field, whereas negative charges tend to move in the direction of the magnetic field. 
• A magnetic field, on the other hand, is produced by moving charges. Similarly, the field exerts a force on the other moving charges in the above step, but the direction and velocity are always perpendicular. 
• Remember that just the direction of the charges is changed in this case, while the speed remains constant.
• Oscillating charged particles produce electromagnetic waves, which are a combination of magnetic and electric fields. 
• When these fields accelerate to the speed of light in free space, the charged particle begins to oscillate about its equilibrium position.

Ques. What are the different types of electromagnetic waves?

Ans. The different types of electromagnetic waves are

• Radio Waves: These waves are produced by rapidly changing electric current in the LC circuit or by accelerated motion of charges in conducting wires.
• Microwaves: These waves are produced by oscillating electrons in a cavity. Oscillators used to produce microwaves are klystron, magnetron, and gun diodes.
• Infra-red Waves: IR waves are produced by the excitation of atoms and molecules. Hot bodies also radiate infrared waves. They are also known as heat waves.
• Visible light: They are emitted when an electron jumps from a higher energy level to a lower energy level of an atom. Visible light gives the sense of sight to human eyes.
• Ultraviolet (UV) Waves: These waves are produced by carbon-arc welding and discharge tubes. The sun is the most important source of UV rays.
• X-rays: X-ray or X-radiation is a high-energy form of electromagnetic radiation. They are well-known for their use in medical imaging. They are employed in the production of sharp monotone images of objects on X-ray films.
• Gamma-rays: They are produced during the radioactive decay of nuclei in nuclear reactions.

---

Very Long Answers Questions [5 Marks Questions]

Ques. What are the different characteristics of electromagnetic waves?

Ans. The following are the different characteristics of electromagnetic waves

• Electromagnetic waves do not require any material medium for their propagation. They can propagate in a vacuum as well as in a medium.
• The speed of electromagnetic waves in free space or vacuum is given by

c = 1/√(µ_o∈_o) = 3 x 10⁸ m/s

• The speed of electromagnetic waves in a medium is given by

v = 1/√(µ∈)

where µ and ∈ are the permeability and permittivity of the medium respectively.

• The nature of the electromagnetic waves is transverse.
• The amplitude of the electric field and magnetic field are related to each other by a relation

E₀/B₀ = c (Speed of electromagnetic wave in air or vacuum).

• Electromagnetic waves carry energy as they travel from one point to another point in space. The average energy density of an electromagnetic wave is given by

U_av = (∈_oE₀²)/2 = B₀²/2µ_o

• The intensity of electromagnetic waves depends on the amplitude of the electric field or magnetic field.
• Electromagnetic waves carry momentum and exert radiation pressure (P) on the surface they fall, and is given as 

P = (1/A)(dP/dt) = I/c

Ques. Calculate the electric field and magnetic fields produced by the radiation coming from a 100 W bulb at a distance of 3 m. Assume the efficiency of the bulb is 2.5% and it is a point source.

Ans. Given

• Power of the bulb, P = 100 W
• Distance of the point from the bulb, r = 3 m
• The efficiency of the bulb, ɳ = 2.5%

The intensity of the radiation emitted from the bulb is given by

I = (Power/Area) x Efficiency

⇒ I = P/(4πr²) x ɳ 

On substituting the values, we get

I = 100/(4 x 3.14 x 3²) x 2.5/100 = 0.022 W m^-2

Intensity (I) is also given by the formula

I = 1/2 x ∈₀cE₀²

But the intensity of the radiation produced by the electric field is half of the total intensity and the remaining half intensity is provided by the magnetic field.

Therefore, the intensity produced by the electric field is given by

I’ = I/2 = 1/4 x ∈₀cE₀²

⇒ E₀² = 2I/∈₀c

⇒ E₀ = √(2I/∈₀c)

On substituting the values, we get

E₀ = √(2 x 0.022/8.854 x 10^-12 x 3 x 10⁸) = 4.1 V m^-1

Hence the magnitude of the electric field produced by the radiation is 4.1 V m^-1

Also, the amplitude of the electric field and magnetic field are related to each other by a relation, 

E₀/B₀ = c

⇒ B₀ = E₀/c

On substituting the values, we get

B₀ = 4.1/(3 x 10⁸) = 1.37 x 10^-8 T

Hence the magnitude of the magnetic field produced by the radiation is 1.37 x 10^-8 T.

Ques. A source of light has an energy flux of 10 W/m². The light falls perpendicular to the surface of an area of 5 cm². If the surface completely absorbs the incident light, then find

1. The momentum delivered to the surface
2. Force exerted on the surface in 10 minutes

Ans. Given

• Energy flux or Intensity of the light, I = 10 W/m²
• Area of the surface, A = 5 cm² = 5 x 10^-4 m²
• Time, t = 10 minutes = 600 seconds

The intensity of the radiation is given by

I = (Energy)/(Area x Time)

⇒ Energy, E = IAt

On substituting the values, we get

E = 10 x 5 x 10^-4 x 600 = 3 joule

1. The momentum delivered to the surface is given by

P = Energy/Speed

⇒ P = 3/(3 x 10⁸) = 10^-8 kg m/s

2. The force exerted on the surface is given by

F = Momentum(P)/Time(t)

⇒ F = 10^-8/600 = 1.6 x 10^-11 N

---

Previous Year Questions

1. Extraction of metal from the ore cassiterite involves...[JEE Advanced 2011]
2. Commonly used vectors for human genome sequencing are...[NEET UG 2014]
3. Interfascicular cambium and cork cambium are formed due to​..
4. Pneumotaxic centre is present in​...[UP CPMT 2007]
5. Reaction of HBr with propene in the presence of peroxide gives….[NEET UG 2004]
6. Assuming the expression for the pressure exerted by the gas on the walls of the container, it can be shown that pressure is...[MHT CET 2016]
7. Which among the following is the strongest acid?...[TS EAMCET 2017]
8. Isopropyl alcohol on oxidation forms​..
9. A vector is not changed if​..
10. Which of the following arrangements does not represent the correct order of the property stated against it?...[JEE Main 2013]

For Latest Updates on Upcoming Board Exams, Click Here: https://t.me/class_10_12_board_updates

---

Check-Out: