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 Quartz prism.

(c) 8000Å to 4000Å 

The band of seven colours formed, when white light passes through an equilateral prism is called  spectrum.

The angle of deviation is maximum for violet when the dispersion of polychromatic light takes place.

(a) No, the image of all letters will not be at the same place. 

(b) Letter V will be raised maximum. This is because the refractive index of a material depends inversely upon the wavelength of light. On the other hand the shift in the image depends directly on the refractive index. Since the refractive index of a material is maximum for violet light, therefore letter V which is written with violet colour is raised the maximum.

 Infrared radiations can be detected by thermopile.

White light is a polychromatic light and has all the seven wavebands present in it.

(i) Monochromatic light : “A light which consists of one colour (or one wave length) only is called monochromatic light)” 

(ii) Polychromatic light : “A light which consists of a mixture of several colours (wave bands) is called polychromatic light”.

X-rays are used in the detection of fracture in bones and teeth.

Visible waves has wavelength range between 4000Å – 8000Å (where 1Å = 10^-10m)

As light passes through atmosphere indigo and blue both scatter because size of particles of present in air goon increasing and sky appears blue because blue light reaches us from particles scattering blue colour which are nearest to the eye.

Since the wavelength of red light is maximum in the visible light, the light of red colour is scattered least by the air molecules of the atmosphere and therefore it can reach to a longer distance. 

(b) red, yellow, green and violet

(a) infrared radiation 

(b) X-rays 

(c) Ultraviolet radiation. 

(a) The high energy invisible electromagnetic rays used in the study of the structure of crystals are X-rays. These X-rays find a wide application in locating the presence of foreign bodies in the human body. 

(b) The speed of the waves of higher wavelength is more i.e., the speed increase with wavelength.

Red colour of longer wave length scatters least by air molecules of atmosphere and red light can be seen from farthest distance (without getting weak) hence are used as fog lights in automobiles. 

Four properties of infra red rays : 

1. l.R. rays are least scattered by fog, mist etc. as they have long wavelength. 

2. They can be detected by a thermopile or a thermometer with a blackend bulb, as they produce heating effect. 

3. They travel with vel. of light i.e. 3 × 10⁸ms^-1 

4. They are electromagnetic wave and hence are not affected by electromagnetic fields. 

Four uses of infra red rays : 

1. They are used to detect diseases in crops which are used to find any change in heat radiation pattern and help in early warning to save crops. 

2. Patients with swollen joints, muscles, etc. feel relieved when exposed to these radiations. 

3. These are used in night vision devices. 

4. They are used in surface to air missiles for tracking and destroying enemy planes. 

Infrared rays : “The electromagnet radiations beyond redend of the visible spectrum are called infrared rays : Their range is 8000Å to 10⁷Å. 

One use of infrared radiation : Used in remote control of t.v. and other gadgets.

Way to detect : 

1. Infrared radiations : It we move a thermometer with blackend bulb from violet to red end of a visible spectrum, there is a slight rise in temperature and if the bulb is moved in the region beyond red, there is sudden rise in temperature, this proves that the region beyond red is not visible and produces heating effect is Infrared region. 

2. Ultraviolet radiations : When a silver chloride (Ag Cl) paper is placed in the region beyond violet, the paper first turns violet, then BROWN and finally black. This proves that there is a region beyond violet which is invisible and produces. Strong chemical effect in silver chloride is known as Ultraviolet regions.

During the Sunset the colour which scatters closest to the eye of observer is  red.

X-rays are produced by  excitation of inner electron of atom and is sudden annihilation of high energy free electrons.

1. It is the most familiar form of EM waves.

2. These waves are detected by human eye. Therefore this wavelength range is called the visible light. 

3. The visible light is emitted due to atomic excitations. 

4. Visible light emitted or reflected from objects around us provides us information about those objects and hence about the surroundings. 

5. Different wavelengths give rise to different colours as shown in the table given below.

The electromagnetic radiation which are useful in night photography is infrared rays.

Infrared rays with very large wavelength are easily reflected by carbon dioxide molecules.

Production:

1. All hot bodies are sources of infrared rays. About 60% of the solar radiations are infrared in nature. 

2. Thermocouples, thermopile and bolometers are used to detect infrared rays.

Properties:

1. When infrared rays are incident on any object, the object gets heated. 

2. These rays are strongly absorbed by glass. 

3. They can penetrate through thick columns of fog, mist and cloud cover.

Uses:

1. Used in remote sensing. 

2. Used in diagnosis of superficial tumours and varicose veins. 

3. Used to cure infantile paralysis and to treat sprains, dislocations and fractures. 

4. They are used in solar water heaters and solar cookers. 

5. Special infrared photographs of the body called thermograms, can reveal diseased organs because these parts radiate less heat than the healthy organs. 

6. Infrared binoculars and thermal imaging cameras are used in military applications for night vision. 

7. Used to keep green house warm. 

8. Used in remote controls of TV, VCR, etc.

(i) → (b) 

(ii) → (a) 

(iii) → (d) 

(iv) → (c)

(a) If assertion and reason both are true and reason is the correct explanation of the assertion.

James Clerk Maxwell was first predicted the existence of EM waves.

(i) → (b) 

(ii) → (a)

(iii) → (d) 

(iv) → (c)

(a) If assertion and reason both are true and reason is the correct explanation of the assertion.

(c) If assertion is true but reason is false.

Hertz experimentally observed that the production of spark between the detection gap is maximum when it is placed parallel to source gap. This means that the electric vector of radiation produced by the source gap is parallel to the two gaps.

Correct answer is (b) IRrays.

Microwaves:

It is produced by electromagnetic oscillators in electric circuits. The wavelength range is 1 x 10^-3 m to 3 x 10^-1 m and frequency range is 3 x 10¹¹ Hz to 1 x 10⁹ Hz. It obeys reflection and polarization. It is used in radar system for aircraft navigation, speed of the vehicle, microwave oven for cooking and very long distance wireless communication through satellites.

X-rays: 

It is produced when there is a sudden deceleration of high speed electrons at high-atomic number target, and also by electronic transitions among the innermost orbits of atoms. The wavelength range 10^-13 m to 10^-8 m and frequency range are 3 x 10²¹ Hz to 1 x 10¹⁶ Hz. X-rays have more penetrating power than ultraviolet radiation.

X-rays are used extensively in studying structures of inner atomic electron shells and crystal structures. It is used in detecting fractures, diseased organs, formation of bones and stones, observing the progress of healing bones. Further, in a finished metal product, it is used to detect faults, cracks, flaws and holes.

Radio waves: 

It is produced by oscillators in electric circuits. The wavelength range is 1 x 10^-1 m to 1 x 10⁴ m and frequency range is 3 x 10⁹ Hz to 3 x 10⁴ Hz. It obeys reflection and diffraction. It is used in radio and television communication systems and also in cellular phones to transmit voice communication in the ultra high frequency band.

Visible light:

It is produced by incandescent bodies and also it is radiated by excited atoms in gases. The wavelength range is 4 x 10^-7 m to 7 x 10^-7 m and frequency range are 7 x 10¹⁴ Hz to 4 x 10¹⁴ Hz. It obeys the laws of reflection, refraction, interference, diffraction, polarization, photo-electric effect and photographic action. It can be used to study the structure of molecules, arrangement of electrons in external shells of atoms and sensation of our eyes.

Correct answer is (a) Less than 3 x 10^-7 m.

Correct answer is (a) X-rays

Correct answer is (d) UV rays.

Correct answer is (d) UV radiation.

In ascending power of frequencies: radiowaves, microwaves, ultraviolet rays, X-rays and gamma rays. Uses of Electromagnetic Spectrum 

(i) γ -rays are highly penetrating, they can penetrate thick iron blocks. Due to high energy, they are used to produce nuclear reactions. γ -rays are produced in nuclear reactions. In medicine, they are used to destroy cancer cells. 

(ii) X-rays are used in medical diagnostics to detect fractures in bones, tuberculosis of lungs, presence of stone in gallbladder and kidney. They are used in engineering to check flaws in bridges. In physics X-rays are used to study crystal structure. 

(iii) Radiowaves are used for broadcasting programmes to distant places. According to frequency range, they are divided into following groups 

(1) Medium frequency band or medium waves 0·3 to 3 MHz 

(2) Short waves or short frequency band 3 MHz — 30 MHz 

(3) Very high frequency (VHF) band 30 MHz to 300 MHz 

(4) Ultrahigh frequency (UHF) band 300 MHz to 3000 MHz 

(iv) Microwaves are produced by special vacuum tubes, namely; klystrons, magnetrons and gunn diodes. Their frequency range is 3 GHz to 300 Ghz. They are used in radar systems used in air craft navigation and microwave users in houses.

The shortwaves (wavelength less than 200m or frequencies greater than 1,500 kHz) are absorbed by the earth due to their high frequency but are effectively reflected by F­layer in the ionosphere. After reflection from the ionosphere, the short waves reach the surface of earth back only at a large distance from the transmitter. For this reason, short waves are used in long distance transmission.

In an electromagnetic wave vector E B, and direction of propagation are mutually perpendicular.

(i) Average surface temperature will be lower. Because there will be no green house effect in absence of atmosphere.

(ii) Since, electromagnetic waves carry both energy and momentum, therefore, they exert pressure on the surface on which they are incident.

Average surface temperature will be lower. This is because there will be no green house effect in absence of atmosphere.

The infra-red radiation emitted by the earth are retained by the earth’s atmosphere due to the green house effect and this keeps the earth warm. If the earth didn’t have atmosphere, its average temperature would have been low.

No, an electromagnetic wave cannot be deflected by magnetic or electric field. It is because, they do not consist of charged particles. They merely propagate in the form of electric and magnetic fields varying both in space and time.

Correct option is: (C) s²/m²

Correct option is: (B) \(\frac{22}{\sqrt{\mu \epsilon}}\)

Scientists estimate that in case of global nuclear war, the clouds produced will cover probably whole of the sky. In that case, solar radiation would be prevented from reaching the earth and it will result in, what they call as nuclear winter on the earth.

1. Maxwell proposed that an oscillating electric charge radiates energy in the form of EM wave. 

2. EM waves are periodic changes in electric and magnetic fields, which propagate through space. 

3. Thus, energy can be transported in the form of EM waves.

Hot bodies lose the heat in the form of radiation.