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This mock test of Test: Electromagnetic Waves - From Past 28 Years Questions for Class 12 helps you for every Class 12 entrance exam.
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QUESTION: 1

Which of the following, is the longest wave ? [1989]

Solution:

Rays - Wavelength

[Range in m]

X-rays - 1 × 10^{–11} to 3 × 10^{–8}

γ-rays - 6 × 10^{–14} to 1 × 10^{–11}

Microwaves - 10^{–3} to 0.3

Radiowaves - 10 to 10^{4}

QUESTION: 2

Pick out the longest wavelength from the following types of radiation. [1990]

Solution:

Wavelength of red light is longest

QUESTION: 3

The frequency of electromagnetic wave, whichis best suited to observe a particle of radius3 × 10^{–4} cm is of the order of [1991]

Solution:

The Wave length of radiation used should be less than the size of the particle =

QUESTION: 4

The structure of solids is investigated by using [1992]

Solution:

X-rays are used for the investigation of

structure of solids

QUESTION: 5

A signal emitted by an antenna from a certainpoint can be received at another point of thesurface in the form of [1993]

Solution:

QUESTION: 6

The oscillating electric and magnetic field vectorsof electromagnetic wave are oriented along [1994]

Solution:

The direction of oscillations of E and B fields are perpendicular to each other as well as to the direction of propagation. So, electromagnetic waves are transverse in nature. The electric and magnetic fields oscillate in same phase.

QUESTION: 7

Which one of the following electromagneticradiations has the smallest wavelength? [1994]

Solution:

Rays - Wavelength

[Range in m]

X-rays - 1 × 10^{–11} to 3 × 10^{–8}

γ-rays - 6 × 10^{–14} to 1 × 10^{–11}

Microwaves - 10^{–3} to 0.3

Radiowaves - 10 to 10^{4}

QUESTION: 8

If ∈_{0} and μ_{0} are the electric permittivity and magnetic permeability in vacuum, ∈ and μ are corresponding quantities in medium, then refractive index of the medium is [1997]

Solution:

We know that velocity of lectromagnetic

wave in vacuum

velocity of electromagnetic wave in

medium is (v) =

Therefore refractive index of the medium

QUESTION: 9

In a circuit, inductance L and capacitance C are connected as shown in the figure. A_{1} and A_{2 }

are ammeters. When key K is pressed to complete the circuit, then just after closing key (K), the readings of A_{1} and A_{2} will be [1999]

Solution:

Initially there is no D.C. current in inductive circuit and maximum D.C. current is in capacitive current. Hence, the current is zero in A_{2} and maximum in A_{1}.

QUESTION: 10

The electromagnetic radiations are caused by [1999]

Solution:

A stationary charge produces electric field only; an uniformly moving charge produces localised electromagnetic field; an accelerated charge produces electromagnetic radiations.

QUESTION: 11

The frequencies of X-rays, γ-rays and ultravioletrays are respectively a, b, and c. Then [2000]

Solution:

γ rays has lowest wavelength and highest frequency among them while ultraviolet ray has highest wavelength and lowest frequency.

Order of frequency : b > a > c

QUESTION: 12

Which of the following is positively charged? [2001]

Solution:

α rays contain Helium nuclei which contains 2 unit of positive charge.

QUESTION: 13

if represent electric and magnetic field vectors of the electromagnetic waves, then the direction of propagation of the waves will be along

Solution:

Direction of propagation of electro-magnetic waves is perpendicular to Electric field and Magnetic field. Hence, direction is given by

QUESTION: 14

Which of the following electromagneticradiations has the least wavelength? [2002]

Solution:

Gamma ray has highest frequency and lowest wavelength.

QUESTION: 15

Green-house effect is the heating up of earth's atmosphere due to [2002]

Solution:

Infrared rays is the cause of Green house effect. The glass transmits visible light and short infrared rays which are absorbed by plants. Then it emits long infrared rays, which are reflected back by glass.

QUESTION: 16

Which one of the following rays is notelectromagnetic wave ? [2003]

Solution:

β ray is not electromagnetic ray

QUESTION: 17

We consider the radiation emitted by the humanbody. Which of the following statements is true? [2003]

Solution:

Depends on the magnitude of frequency

QUESTION: 18

If λ_{v}, λ_{x} and λ_{m} represent the wavelengths of visible light, X–rays and microwaves respectively, then

Solution:

We know

QUESTION: 19

The electric and magnetic field of an electromagneticwave are [2007]

Solution:

Variation in magnetic field causes electric field and vice-versa.

In electromagnetic waves, .

Both and are in the same phase.

In electromagnetic waves

E = E0 sin(ωt - kx)

B = B0 sin(ωt - kx)

The electromagnetic waves travel in the

direction of

QUESTION: 20

The velocity of electromagnetic radiation in a medium of permittivity ∈_{0} and permeability μ_{0} is given by [2008]

Solution:

The velocity of electromagnetic radiation

in a medium of permittivity ∈_{0 }and

permeability μ_{0 }is equal to

QUESTION: 21

The electric field part of an electromagnetic wave in a medium is represented by E_{x}=0;

E_{z} = 0. The wave is : [2009]

Solution:

Comparing with the equation of wave

QUESTION: 22

Which of the following statement is false for theproperties of electromagnetic waves? [2010]

Solution:

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

QUESTION: 23

The electric and the magnetic field associated with an E.M. wave, propagating along the +z-axis, can be represented by [2011]

Solution:

The electromagnetic wave is propagating along the +z axis.

Since the electric and magnetic fields are perpendicular to each other and also perpendicular to the direction of propagation of wave.

Also. gives the direction of wave propagation.

QUESTION: 24

The decreasing order of wavelength of infrared,microwave, ultraviolet and gamma rays is [2011]

Solution:

The decreasing order of the wavelengths is as given below :

microwave, infrared, ultraviolet, gamma

rays.

QUESTION: 25

The electric field associated with an e.m. wave in vacuum is given by cos (kz – 6 ×10^{8}t), where E, z and t are in volt/m, meter and seconds respectively. The value of wave vector k is : [2012]

Solution:

On comparing the given equation to

QUESTION: 26

The ratio of amplitude of magnetic field to theamplitude of electric field for an electromagneticwave propagating in vacuum is equal to : [2012M]

Solution:

The average energy stored in the electric field

The average energy stored in the magnetic field

According to conservation of energy

QUESTION: 27

An electromagnetic wave of frequency v = 3.0MHz passes from vacuum into a dielectricmedium with relative permittivity ε = 4.0. Then[NEET Kar. 2013]

Solution:

Given: frequency f = 2MHz, relative

permittivity ∈_{r}= 4

From formula,

velocity

[Since frequency remains unchanged]

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