NEET
Practice Test 4
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DIRECTIONS: Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer(ONLY ONE option is correct ) from the following-

Statement 1 : Radio waves can be polarised.

Statement 2 :Sound waves in air are longitudinal in nature.

 

  • Solution

    (c)Statement -1 is true, Statement-2 is true; Statement-2 is not a correct explanation for Statement-1

    Radio waves can be polarised because they are transverse in nature. Sound waves in air are longitudinal in nature.

DIRECTIONS: Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer(ONLY ONE option is correct ) from the following-

Statement 1 :The earth without atmosphere would be inhospitably cold.

Statement 2 :All heat would escape in the absence of atmosphere.

 

  • Solution

    (b)Statement -1 is true, Statement-2 is true; Statement -2 is a correct explanation for Statement-1

    In the absence of atmosphere, all the heat will escape from earth’s surface which will make earth in hospitably cold.

DIRECTIONS: Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer(ONLY ONE option is correct ) from the following-

 

Statement 1 : Environmental damage has increased the amount of ozone in the atmosphere.

Statement 2 :Increase of ozone increases the amount of ultraviolet radiation on earth.

  • Solution

    (a)Statement -1 is false, Statement-2 is true

    Ozone layer in the stratosphere helps in protecting life of organism form ultraviolet radiation on earth. Ozone layer is depleted due to of several factors like use of chlorofluorocarbon (CFC) which is the cause of environmental damages.

DIRECTIONS: Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer(ONLY ONE option is correct ) from the following-

Statement 1 : Ultraviolet radiations of higher frequency waves are dangerous to human being.

Statement 2 :Ultraviolet radiation are absorbed by the atmosphere.

  • Solution

    (c)Statement -1 is true, Statement-2 is true; Statement-2 is not a correct explanation for Statement-1

    The wavelength of these wave ranges between 4000 Å to 100 Å that is smaller wavelength and higher frequency. They are absorbed by atmosphere and convert oxygen into ozone. They cause skin diseases and they are harmful to eye and cause permanent blindness.

DIRECTIONS: Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer(ONLY ONE option is correct ) from the following-

Statement 1 :Television signals are received through sky-wave propagation.

Statement 2 :The ionosphere reflects electromagnetic waves of frequencies greater than a certain critical frequency.

  • Solution

    (a)Statement -1 is false, Statement-2 is true

    In sky wave propagation , the radio waves having frequency range 2 MHz to 30 MHz are reflected back by the ionosphere. Radio waves having frequency nearly greater than 30 MHz penetrates the ionosphere and is not reflected back by the ionosphere. The TV signal having frequency greater than 30 MHz therefore cannot be propagated through sky wave propagation.In case of sky wave propagation, critical frequency is defined as the highest frequency is returned to the earth by the considered layer of the ionosphere after having sent straight to it. Above this frequency, a wave will penetrate the ionosphere and not reflected by it.

DIRECTIONS: Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer(ONLY ONE option is correct ) from the following-

Statement 1 : Shortwave bands are used for transmission of radio waves to a large distance.

Statement 2 :Short waves re reflected by ionosphere

 

  • Solution

    (c)Statement -1 is true, Statement-2 is true; Statement-2 is not a correct explanation for Statement-1

    Short wave (wavelength 30 km to 30 cm). These waves are used for radio transmission and for general communication purpose to a longer distance from ionosphere.

DIRECTIONS: Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer(ONLY ONE option is correct ) from the following-

Statement 1 :When variable frequency a.c. source is connected to a capacitor, displacement current in creases with increase in frequency.

Statement 2 : As frequency increases conduction current also increases.

 

  • Solution

    (b)Statement -1 is true, Statement-2 is true; Statement -2 is a correct explanation for Statement-1

The condition under which a microwave oven heats up a food item containing water molecules most efficiently is

  • Solution

    Required condition : Frequency of microwaves =Resonant frequency of water molecules.

The ratio of amplitude of magnetic field to the amplitude of electric field for an electromagnetic wave propagating in vacuum is equal to

  • Solution

The electric field associated with an e.m. wave in vacuum is given by \(\overrightarrow{E}=\hat{i}\, 40\, cos(kz-6\times 10^{8}\iota )\), where E, z and t are in volt/m, meter and seconds respectively. The value of wave vector k is

  • Solution

The electric and the magnetic field associated with an E.M.wave, propagating along the +z-axis, can be represented by

  • Solution

    E.M. wave always propagates in a direction perpendicular to both electric and magnetic fields. So,electric and magnetic fields should be along + X and +Y-directions respectively. Therefore, option (a) is the correct option.

Which of the following statement is false for the properties of electromagnetic waves?

  • Solution

    Electromagnetic waves are the combination of mutually perpendicular electric and magnetic fields. So, option(c) is false.

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ELECTROMAGNETIC WAVES
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