Electromagnetic Waves & Spectrum Test - 1

CONCEPT:

• Electromagnetic waves: It is a transverse wave defined as composed of oscillating electrical and magnetic fields perpendicular (90°) to each other.
• The Speed of electromagnetic waves is the same as of speed of light c = 3 × 10⁸ m/s.

EXPLANATION:

• James Clerk Maxwell: He is a Scottish Mathematical physicist. He proposed equations of Magnetism (Maxwell’s equations of electromagnetism) and predicted that electromagnetic waves exist but didn’t discover it.
• Heinrich Rudolf Hertz: He is a German physicist who conclusively proved the existence of electromagnetic waves. The unit of frequency, Cycles per second was named Hertz in his honour.
• Michael Faraday: He is an English Scientist who discovered principles of Electromagnetic induction, Electrolysis and Diamagnetism. The SI Unit of capacitance is Farad in his honour
• Hans Christian Oersted: He was a Danish physicist who finds out that electric current creates a magnetic field.

So, Option 2 is correct.

The correct answer is option 3) i.e. Velocity

CONCEPT:

• Electromagnetic spectrum: It is the arrangement of electromagnetic radiations according to their frequency or wavelength.
  • ​The electromagnetic spectrum has a range of frequencies, wavelengths, and photon energies.
  • Typically, electromagnetic waves travel at the speed of light in a vacuum. 
  • The electromagnetic spectrum is as follows: 

​

EXPLANATION:

• The velocity of an electromagnetic wave (c) in a vacuum is related to its wavelength (λ) and frequency (f) as follows:

f = cλ 

• As we go from gamma rays to radio waves, the frequency decreases, and the wavelength increases.
• Hence, the velocity (c = 3 × 10⁸ m/s) is constant.

CONCEPT:

Electromagnetic waves or EM waves:

• The waves that are formed as a result of vibrations between an electric field and a magnetic field and they are perpendicular to each other and to the direction of the wave is called an electromagnetic wave.
• The accelerating charged particle produces an electromagnetic (EM) wave.
• A charged particle oscillating about an equilibrium position is an accelerating charged particle.
• Electromagnetic waves do not require any matter to propagate from one place to another as it consists of photons. They can move in a vacuum.

EXPLANATION:

• For free-space transmission, it wouldn't be good to use "high" energy radiation such as gamma rays, ultraviolet rays, and x-rays because they could be dangerous for people's health. Also, the air can scatter high-energy radiation (we see a blue sky because of this scattering of blue and violet light for instance).
• Radio waves have a wavelength varying from a millimeter to 10 km.
• The higher the frequency of the electromagnetic wave, the more it penetrates into the atmosphere.
• The frequency of the radio waves is less than 3×10¹¹ Hz.
• The frequency of the microwaves is varying from 3×1011 Hz to 10¹³ Hz.
• Since low-frequency radio waves are stopped by the earth's atmosphere, and some radio waves are reflected back by the part of the earth's atmosphere.
• So Microwaves are preferred in order to communicate with the artificial satellites which are orbiting the earth at a particular height from the surface of the earth. Microwaves are preferred because they can penetrate through the Earth's atmosphere very easily and reach the target satellite.
• Hence, option 2 is correct.

The correct answer is X-rays.

Concept:

• Electromagnetic spectrum: The complete range of light that exists in nature is called an electromagnetic spectrum.
• Light is an electromagnetic wave and the distance between two successive crests or two successive troughs of the light wave is called a wavelength of the light wave.
• The wavelength of light is denoted by λ.
• As shown in the spectrum, the wavelength increases when we go from left to right.

From the spectrum, we can see that the X rays has the maximum frequency and least wavelength as compared to UV, Microwave and Infrared rays. 

CONCEPT:

• Electromagnetic waves or EM waves: The waves that are formed as a result of vibrations between an electric field and a magnetic field and they are perpendicular to each other and to the direction of the wave is called an electromagnetic wave.
  • The accelerating charged particle produces an electromagnetic (EM) wave.
  • A charged particle oscillating about an equilibrium position is an accelerating charged particle.
  • Electromagnetic waves do not require any matter to propagate from one place to another as it consists of photons. They can move in a vacuum.

Properties of electromagnetic waves:

• EM waves don't have any charge or we can say that they are neutral.
• Propagate as a transverse wave.
• They move with the velocity the same as that of light i.e 3 × 108 m/s.
• It contains energy and they also contain momentum.
• They can travel in a vacuum also.

EXPLANATION:

• Since the electromagnetic waves are neutral.
• So it doesn't transport electric charge.
• Hence option 2 is correct.
• EM waves can transport energy and momentum.

The correct answer is an Infrared wave.

Key Points

Explanation:

• Infrared rays:
  • It is a part of the EM spectrum and has wavelengths ranging from about 700 nanometers (nm) to 1 millimetre (mm).
  • it has longer wavelengths than visible light.
  • Infrared cameras and telescopes or night-vision goggles etc, use infrared waves to sense or measure the heat radiated by the object.
  • Infrared energy radiated from the hot objects can be detected and then converted into an electronic signal to produce a visual image by cameras telescopes.

So, Infrared wave is utilized in the night visionary equipment.

Additional Information

 Microwave: 

• Microwaves are electromagnetic waves with wavelengths ranging from 1m to 1mm (frequencies between 300 MHz and 300 GHz).
• Microwaves can be used to heat and cook food. It is also used for communications, especially for extending TV signals to larger distances.

Radio Wave:

• Radio waves are electromagnetic waves with frequencies between 300 GHz and 3kHz.
• They are used for communications, broadcast television signals, RADARS, Cameras, etc

CONCEPT:

Sound: 

• A sound is a form of energy that produces a sensation of hearing in our ears.
• It is a kind of disturbance that travels through a medium due to repeated vibrations of the particles of the medium about their mean positions.
• The disturbance being handed over from one particle to the next.

Light:

• Light is a form of electromagnetic radiation that can be detected by the human eye.
• When light falls on an object, some part of the light is reflected on our eyes and we are able to see.

EXPLANATION:

• Sound waves are longitudinal waves and light waves are transverse waves. 
• As we know sound waves are longitudinal waves and travel through compression and rarefactions in the medium on the other hand light waves are transverse in nature and do not require medium to travel. Therefore option 3 is incorrect.
• As we know that, the sound wave and lightwave travels with different velocity and have a different frequency, therefore the wavelength (λ = v/f) is different for both. 
• Both sound and light waves follow the law of reflection i.e. the angle of incidence is equal to the angle of reflection. 

CONCEPT:

• Electromagnetic waves: It is a transverse wave defined as composed of oscillating electrical and magnetic fields perpendicular to each other.

​

• Electromagnetic waves are transverse in nature. They travel from transmitter to receiver in three different modes.
• Ground waves are those electromagnetic waves which travel from transmitter to receiver across the Earth's surface. They suffer energy losses due to bending.
• Skywaves are those electromagnetic waves that travel through reflection from the ionospheric layer from the transmitter to the receiver.
• Space waves travel directly from the transmitter to the receiver.

EXPLANATION:

As from the above discussion,

• Ground waves are those electromagnetic waves which travel from transmitter to receiver across the Earth's surface. They suffer energy losses due to bending. So option 1 follows.
• Skywaves are those electromagnetic waves that travel through reflection from the ionospheric layer from the transmitter to the receiver. So option 2 follows.
• Space waves travel directly from the transmitter to the receiver. So option 3 follows.
• Electromagnetic waves are longitudinal in nature. It is not correct, Electromagnetic waves are transverse in nature. So option 4 does not follow.

​

 So option 4 is correct because it is a false statement.

The correct answer is Radio wave.

Key Points

CONCEPT:

Electromagnetic waves or EM waves:

• The waves that are formed as a result of vibrations between an electric field and a magnetic field and are perpendicular to each other and to the direction of the wave is called an electromagnetic wave.
  • The accelerating charged particle produces an electromagnetic (EM) wave.
  • A charged particle oscillating about an equilibrium position is an accelerating charged particle.
  • Electromagnetic waves do not require any matter to propagate from one place to another as it consists of photons. They can move in a vacuum.
  • The electromagnetic spectrum is the arrangement of electromagnetic waves in the increasing order of wavelength.

EXPLANATION:

​

• As we can see in the em waves spectrum, the radio wave has the maximum wavelength.
• Hence option 3 is correct.

Additional Information

Properties of electromagnetic waves:

1. Not have any charge or we can say that they are neutral.
2. Propagate as a transverse wave.
3. They move with the velocity the same as that of light i.e 3 × 108 m/s.
4. It contains energy and they also contain momentum.
5. They can travel in a vacuum also.

CONCEPT:

• Electromagnetic waves or EM waves: The waves that are formed as a result of vibrations between an electric field and a magnetic field and they are perpendicular to each other and to the direction of the wave is called an electromagnetic wave.
• The accelerating charged particle produces an electromagnetic (EM) wave.
• A charged particle oscillating about an equilibrium position is an accelerating charged particle.
• Electromagnetic waves do not require any matter to propagate from one place to another as it consists of photons. They can move in a vacuum.

Properties of electromagnetic waves:

• Not have any charge or we can say that they are neutral.
• Propagate as a transverse wave.
• They move with the velocity the same as that of light i.e 3 × 108 m/s.
• It contains energy and they also contain momentum.
• They can travel in a vacuum also.

EXPLANATION:

• From above it is clear that Electromagnetic waves do not require any matter to propagate from one place to another as it consists of photons. Therefore option 1 is correct.
• In an electromagnetic wave, the electric field and magnetic field vary continuously with maxima and minima at the same place and same time. Therefore option 2 is correct.
• The energy in an electromagnetic wave is divided equally between electric and magnetic fields. Therefore option 3 is correct. 
• An electromagnetic wave is a perpendicular variation in both the electric field(E) and Magnetic field(B). Therefore option 4 is incorrect.

• Electromagnetic waves move with the velocity of light in free space. Given by

\(C =\frac{1}{\sqrt{μ_{0}ε_{0} }}\)

Where C =  Velocity of light,ε0 =Permitivity of free space, μ0 =Permiability of free space 

• In a material medium Electromagnetic wave moves with velocity V which is not equal to the velocity of light, given by

\(V =\frac{1}{\sqrt{με }}\)

Where μ  =Permiability of free space, ε = Permeability of medium

• The amount of energy imparted by an electromagnetic wave in unit volume while passing through a medium is termed as energy density, given by

\(U = U_{E} + U _{B} = \frac{\varepsilon_0 E^{2}}{2} +\frac{B_0^{2}}{2\mu_0}\)

Where E = Electric field, B = Magnetic field, B0 = Magnetic field,ε0 =Permitivity of free space, μ0 =Permiability of free space