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(a), (d)

(a) The associated magnetic field is given as

B=1/C(E₁i-E₂j)cos(kz −ωt).

(d) The given electromagnetic wave is plane polarised.

It is given that E=(E₁i+E₂j)cos(kz −ωt)

In EM wave that associate magnetic field vector B=1/C(E₁i-E₂j)cos(kz −ωt) option a is true

Also E

and B are perpendicular to each other and the propagation of EM wave is perpendicular to E as well as B

The given electromagnetic wave is plane polarized.

option (a), (d) both are correct

(a) The associated magnetic field is given as

B=1/C(E₁i-E₂j)cos(kz −ωt).

(d) The given electromagnetic wave is plane polarized.

(b), (d)

(b) E_y, B_z.

(d) E_z, B_y.

(a), (b), (c)

(a) The associated magnetic field is given as B=1/c k x E=1/ω(k X E).

(b) The electromagnetic field can be written in terms of the associated magnetic field as E=c(B x k).

(c) k.E = 0, k.B=0.

Microwaves are used in aircraft navigation, (speed guns to time fast balls, tennis serves, and automobiles). Microwaves are also used in microwave ovens. 

IR-waves from the sun keep the earth warm and hence help to sustain life on the earth IR rays photographs are used for weather forecasting. (They are used in detectors, remote switches) 

The electric current due to changing electric field is called displacement current.

1. SI unit of frequency of electromagnetic waves is hertz (Hz).

2. Higher frequencies are represented by kHz, MHz, GHz etc.

[Note: 1 kHz = 10³ Hz, 1 MHz = 10⁶ Hz. 1 GHz = 10⁹ Hz]

Highly focused UV-rays are used in eye surgery (LASIK-Laser Assisted in situ ketatomileusis). UV-lamps are used to kill germs in water purifiers. 

Electromagnetic waves are non-mechanical waves which move with speed equals to the speed of light (in vacuum).

An accelerated charged particle is the source of e.m. waves.  

Yes, it is a source of magnetic field. 

The displacement current can be defined as the current which comes into play in the region in which the electric field and the electric flux are changing with time.

1. Maxwell pointed a major flaw in the Ampere’s law for time dependant fields.

2. He noticed that the magnetic field can be generated not only by electric current but also by changing electric field.

3. Therefore, he added one more term to the equation describing Ampere’s law. This term is called the displacement current.

Consider a charge oscillating with some frequency. This is an example of accelerating charge. This charge produces an oscillating electric field in space. This field, in turn, produces an oscillating magnetic field in the neighborhood. 

The process continues because the oscillating electric and magnetic fields regenerate each other. Hence an electromagnetic wave originates from the accelerating charges. 

Momentum transferred, p = u/c where u = energy transferred and c = speed of light Due to the large value of speed of light (c),the amount of momentum transferred by the em waves incident on the surface is small.

This is because the special glass goggles protect the eyes from large amount of UV radiations produced by welding arcs.

 Infrared waves are called heat waves because water molecules present in the materials readily absorb the infra red rays get heated up. 

Application: They are used in green bouses to warm the plants.

Light waves are electromagnetic waves which can travel in vacuum whereas sound waves travel due to the vibration of particles of medium. Without any particles present (like in a vacuum) no vibrations can be produced. Hence, the sound wave cannot travel through the vacuum.

Production:

1. German physicist W. C. Rontgen discovered X-rays while studying cathode rays. Hence, X-rays are also called Rontgen rays. 

2. Cathode ray is a stream of electrons emitted by the cathode in a vacuum tube. 

3. X-rays are produced when cathode rays are suddenly stopped by an obstacle.

Properties:

1. They are high energy EM waves. 

2. They are not deflected by electric and magnetic fields. 

3. X-rays ionize the gases through which they pass. 

4. They have high penetrating power. 

5. Their over dose can kill living plant and animal tissues and hence are harmful.

Uses:

1. Useful in the study of the structure of crystals. 

2. X-ray photographs are useful to detect bone fracture. X-rays have many other medical uses such as CT scan. 

3. X-rays are used to detect flaws or cracks in metals. 

4. These are used for detection of explosives, opium etc.

Production :

1. Ultraviolet rays can be produced by the mercury vapour lamp, electric spark and carbon arc lamp. 

2. They can also be obtained by striking electrical discharge in hydrogen and xenon gas tubes. 

3. The Sun is the most important natural source of ultraviolet rays, most of which are absorbed by the ozone layer in the Earth’s atmosphere.

Uses :

1. Ultraviolet rays destroy germs and bacteria and hence they are used for sterilizing surgical instruments and for purification of water.

2. Used in burglar alarms and security systems. 

3. Used to distinguish real and fake gems.

It covers wavelengths ranging from about 4 × 10^–7 m (400 nm) down to 6 × 10^–10m (0.6 nm). Ultraviolet (UV) radiation is produced by special lamps and very hot bodies. The sun is an important source of ultraviolet light. But fortunately, most of it is absorbed in the ozone layer in the atmosphere at an altitude of about 40 – 50 km. UV light in large quantities has harmful effects on humans. Exposure to UV radiation induces the production of more melanin, causing tanning of the skin. UV radiation is absorbed by ordinary glass. Hence, one cannot get tanned or sunburn through glass windows. 

Welders wear special glass goggles or face masks with glass windows to protect their eyes from large amount of UV produced by welding arcs. Due to its shorter wavelengths, UV radiations can be focussed into very narrow beams for high precision applications such as LASIK (Laserassisted in situ keratomileusis) eye surgery. UV lamps are used to kill germs in water purifiers. Ozone layer in the atmosphere plays a protective role, and hence its depletion by chlorofluorocarbons (CFCs) gas (such as freon) is a matter of international concern. 

Infrared waves are produced by hot bodies and molecules. This band lies adjacent to the low frequency or long-wave length end of the visible spectrum. Infrared waves are sometimes referred to as heat waves. This is because water molecules present in most materials readily absorb infrared waves (many other molecules, for example, CO₂, NH₃, also absorb infrared waves). After absorption, their thermal motion increases, that is, they heat up and heat their surroundings. Infrared lamps are used in physical therapy. Infrared radiation also plays an important role in maintaining the earth’s warmth or average temperature through the greenhouse effect. Incoming visible light (which passes relatively easily through the atmosphere) is absorbed by the earth’s surface and reradiated as infrared (longer wavelength) radiations. This radiation is trapped by greenhouse gases such as carbon dioxide and water vapour. Infrared detectors are used in Earth satellites, both for military purposes and to observe growth of crops. Electronic devices (for example semiconductor light emitting diodes) also emit infrared and are widely used in the remote switches of household electronic systems such as TV sets, video recorders and hi-fi systems.

(a) Radio waves : Radio waves are produced by the accelerated motion of charges in conducting wires. They are used in radio and television communication systems. They are generally in the frequency range from 500 kHz to about 1000 MHz. The AM (amplitude modulated) band is from 530 kHz to 1710 kHz. Higher frequencies upto 54 MHz are used for short wave bands. TV waves range from 54 MHz to 890 MHz. The FM (frequency modulated) radio band extends from 88 MHz to 108 MHz. Cellular phones use radio waves to transmit voice communication in the ultrahigh frequency (UHF) band. 

(b) Microwaves : Microwaves (short-wavelength radio waves), with frequencies in the gigahertz (GHz) range, are produced by special vacuum tubes (called klystrons, magnetrons and Gunn diodes). Due to their short wavelengths, they are suitable for the radar systems used in aircraft navigation. Radar also provides the basis for the speed guns used to time fast balls, tennisserves, and automobiles. Microwave ovens are an interesting domestic application of these waves. In such ovens, the frequency of the microwaves is selected to match the resonant frequency of water molecules so that energy from the waves is transferred efficiently to the kinetic energy of the molecules. This raises the temperature of any food containing water. 

(c) Infrared waves : Infrared waves are produced by hot bodies and molecules. This band lies adjacent to the low frequency or long-wave length end of the visible spectrum. Infrared waves are sometimes referred to as heat waves. This is because water molecules present in most materials readily absorb infrared waves (many other molecules, for example, CO₂, NH₃, also absorb infrared waves). After absorption, their thermal motion increases, that is, they heat up and heat their surroundings. Infrared lamps are used in physical therapy. Infrared radiation also plays an important role in maintaining the earth’s warmth or average temperature through the greenhouse effect. Incoming visible light (which passes relatively easily through the atmosphere) is absorbed by the earth’s surface and reradiated as infrared (longer wavelength) radiations. This radiation is trapped by greenhouse gases such as carbon dioxide and water vapour. Infrared detectors are used in Earth satellites, both for military purposes and to observe growth of crops. Electronic devices (for example semiconductor light emitting diodes) also emit infrared and are widely used in the remote switches of household electronic systems such as TV sets, video recorders and hi-fi systems. 

(d) Visible rays : It is the most familiar form of electromagnetic waves. It is the part of the spectrum that is detected by the human eye. It runs from about 4 × 10¹⁴ Hz to about 7 × 10¹⁴ Hz or a wavelength range of about 700 – 400 nm. Visible light emitted or reflected from objects around us provides us information about the world. Our eyes are sensitive to this range of wavelengths. Different animals are sensitive to different range of wavelengths. For example, snakes can detect infrared waves, and the ‘visible’ range of many insects extends well into the utraviolet. 

(e) Ultraviolet rays : It covers wavelengths ranging from about 4 × 10^–7 m (400 nm) down to 6 × 10^–10m (0.6 nm). Ultraviolet (UV) radiation is produced by special lamps and very hot bodies. The sun is an important source of ultraviolet light. But fortunately, most of it is absorbed in the ozone layer in the atmosphere at an altitude of about 40 – 50 km. UV light in large quantities has harmful effects on humans. Exposure to UV radiation induces the production of more melanin, causing tanning of the skin. UV radiation is absorbed by ordinary glass. Hence, one cannot get tanned or sunburn through glass windows. Welders wear special glass goggles or face masks with glass windows to protect their eyes from large amount of UV produced by welding arcs. Due to its shorter wavelengths, UV radiations can be focussed into very narrow beams for high precision applications such as LASIK (Laserassisted in situ keratomileusis) eye surgery. UV lamps are used to kill germs in water purifiers. Ozone layer in the atmosphere plays a protective role, and hence its depletion by chlorofluorocarbons (CFCs) gas (such as freon) is a matter of international concern. 

(f) X-rays : Beyond the UV region of the electromagnetic spectrum lies the X-ray region. We are familiar with X-rays because of its medical applications. It covers wavelengths from about 10^–8 m (10 nm) down to 10^–13 m (10^–4 nm). One common way to generate X-rays is to bombard a metal target by high energy electrons. X-rays are used as a diagnostic tool in medicine and as a treatment for certain forms of cancer. Because X-rays damage or destroy living tissues and organisms, care must be taken to avoid unnecessary or over exposure. 

(g) Gamma rays : They lie in the upper frequency range of the electromagnetic spectrum and have wavelengths of from about 10^–10m to less than 10^–14m. This high frequency radiation is produced in nuclear reactions and also emitted by radioactive nuclei. They are used in medicine to destroy cancer cells.

Greenhouse effect is the phenomenon which keeps the earth’s surface warm at night. The earth reflects back infra red part of solar radiation. Infra-red rays are reflected back by low lying clouds and lower atmosphere and keep the earth’s surface warm at night.

Microwaves are produced due to oscillating currents in special vacuum tubes like Klystroms

1. When a radio wave from a transmitting antenna propagates near surface of the Earth so as to reach the receiving antenna, the wave propagation is called ground wave or surface wave propagation.

2. In this mode, radio waves travel close to the surface of the Earth and move along its curved surface from transmitter to receiver.

3. The radio waves induce currents in the ground and lose their energy by absorption. Therefore, the signal cannot be transmitted over large distances. 

4. Radio waves having frequency less than 2 MHz (in the medium frequency band) are transmitted by ground wave propagation. 

5. This is suitable for local broadcasting only. For TV or FM signals (very high frequency), ground wave propagation cannot be used.

Skip distance is the shortest distance from a transmitter measured along the surface of the Earth at which a sky wave of fixed frequency (if greater than critical frequency) will be returned to the Earth so that no sky waves can be received within the skip distance.

Critical frequency is the maximum value of the frequency of radio wave which can be reflected back to the Earth from the ionosphere when the waves are directed normally to ionosphere.

i. When the radio waves from the transmitting antenna reach the receiving antenna either directly along a straight line (line of sight) or after reflection from the ground or satellite or after reflection from troposphere, the wave propagation is called space wave propagation.

ii. The radio waves reflected from troposphere are called tropospheric waves.

iii. Radio waves with frequency greater than 30 MHz can pass through the ionosphere (60 km – 1000 km) after suffering a small deviation. 

Hence, these waves cannot be transmitted by space wave propagation except by using a satellite.

iv. Also, for TV signals which have high frequency, transmission over long distance is not possible by means of space wave propagation.

1. According to quantum theory, an electron, while orbiting around the nucleus in a stable orbit does not emit EM radiation even though it undergoes acceleration. 

2. It will emit an EM radiation only when it falls from an orbit of higher energy to one of lower energy. 

3. EM waves (such as X-rays) are produced when fast moving electrons hit a target of high atomic number (such as molybdenum, copper, etc.).

4. An electric charge at rest has an electric field in the region around it but has no magnetic field. 

5. When the charge moves, it produces both electric and magnetic fields. 

6. If the charge moves with a constant velocity, the magnetic field will not change with time and hence, it cannot produce an EM wave. 

7. But if the charge is accelerated, both the magnetic and electric fields change with space and time and an EM wave is produced. 

8. Thus, an oscillating charge emits an EM wave which has the same frequency as that of the oscillation of the charge.

Waves that are caused by the acceleration of charged particles and consist of electric and magnetic fields vibrating sinusoidally at right angles to each other and to the direction of propagation are called EM waves or EM radiation.

Microwaves are used in radar systems for identifying the location of distant objects like ships, aeroplanes etc.

Correct answer is (B) IR

a₁ = 2.5 a₂

To find: \(\frac{I_1}{I-2}\)

Formula: I ∝ a²

Calculation: From formula,

\(\frac{I_1}{I_2}=(\frac{a_1}{a_2})^2=(\frac{2.5_{a2}}{a_2})\) = (2.5)² = 6.25

Some sources of EM radiation include sources in the cosmos (e.g., the sun and stars), radioactive elements, and manufactured devices. EM exhibits a dual wave and particle nature.

(c) electric energy density is equal to the magnetic energy density.

Accelerated charge is a source of Electromagnetic radiation.

Correct answer is (b) [L²T²].

Correct answer is (d) 900 V m^-1 .

The signals in communication system (e.g. music, speech etc.) are low frequency signals and cannot be transmitted over large distances. In order to transmit the signal to large distances, it is superimposed on a high frequency wave (called carrier wave). This process is called modulation.

1. Without a carrier wave, the input signals could be carried by very low frequency electromagnetic waves but it will need quite a bit of amplification in order to transmit those very low frequencies. 

2. The input signals themselves do not have much power and need a fairly large antenna in order to transmit the information. 

3. Hence, it is necessary to impose the input signal on carrier wave as it requires less power in order to transmit the information.

An audio signal has low frequency (<20 kHz) and low frequency signals cannot be transmitted over large distances. Because of this, a high frequency carrier waves are used for transmission.

(a) The values shown by Shalini are :

(i) high degree of general awareness/

(ii) ability to take quick decisions,

(iii) concern for her aunt,

(iv) helping and caring nature

(b) In microwave oven, microwaves of required wavelength get strongly absorbed by water due to its energy which heated the water. Since every food items has lot of water, so they can be heated and cooked quickly in a microwave over. With this, the microwaves heat the food item completely, not simply from outside as in case of normal oven.

The subjective property of light related to its wavelength is frequency. 

Four properties of ultra violet : 

1. They are electromagnetic waves and are not effected by: Electric Or Magnetic fields. 

2. They obey the laws of refraction and reflection.

3. They travel with velocity 3 × 10⁵km/sec 

4. “I’hey produce chemical effect in silver salts.

Ultraviolet spectrum : “The region of spectrum which extends beyond the violet colour of visible spectrum is called ultraviolet spectrum.”

Angstrom unit (Å) is equal to  10^-10.

Spectrum obtained is impure as colours overlap each other.

Colour : “Is a sensation produced in the brain and is not some thing material.” 

Or 

“Is a sensation produced in the brain due to excitation of the retina, by an electromagnetic wave of some particular wave length.

(i) Dispersion of light : “The phenomenon of splitting white light into its components (seven colours) when passed through a prisms is called dispersion.” 

(ii) Spectrum : “The band of colours obtained on the screen when a polychromatic (white) light splits into seven colours is called spectrum.”