Electromagnetic Waves Test

Result

Electromagnetic Waves Test - 29

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Question 1
1 / -0

The smaller the wavelength of light

A
The larger its frequency.

B
The smaller its frequency.

C
The greater its velocity in a vacuum.

D
The redder it will be.

Solution
Question 2
1 / -0

For an EM Wave, $$E = E_0 \sin 12\times 10^6 [ Z - 2\times 10^8t] \dfrac{N}{C}$$ In a medium, then its refractive index is

A
$$\dfrac{2}{3}$$

B
$$\dfrac{3}{2}$$

C
$$\dfrac{4}{3}$$

D
$$\dfrac{5}{3}$$

Solution

EM wave equation in medium
$$ = E_{0} sin (kz-wt) $$
and $$ w/k = v $$
where v is the velocity of light in medium
subtitling w and k from given equation
$$ v = \dfrac{12\times 10^{6}\times 2\times 10^{8}}{12\times 10^{6}} = 2\times 10^{8} $$
Refractive index $$ = \dfrac{e}{v} = \frac{3\times 10^{8}}{2\times 10^{8}} = \dfrac{3}{2} $$
Question 3
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If $$P$$ represents radiation pressure, $$c$$ represents speed of lights and $$l$$ represents radiation energy striking a unit area per second, then non -zero integers $$x,y$$ and $$z$$ such that $$P^ xl^ yc^z$$ is dimensionless are

A
$$x=0, y=0, z=0$$

B
$$x=1, y=-1, z=1$$

C
$$x=-1, y=1, z=1$$

D
$$x=1, y=1, z=1$$

Solution
Question 4
1 / -0

The displacement current flows in a dielectric of a capacitor when the potential difference across its plates:

A
Has assumed constant value

B
Is decreasing with time

C
Is increasing with position

D
is zero

Solution

Hint:- Use maxwell law of displacement current.
Explanation:-
According to Maxwell's hypothesis, a displacement current will flow through a capacitor when the potential difference across its plates is varying. Thus a varying electric field will exist between the plates and this displacement current is same in magnitude to the current flowing in outer circuit. When a D.C voltage applied across its plates, constant voltage appears across its plates and so there will be no displacement current flowing through the capacitor. Thus the displacement current will flow when the potential is increasing with time.
Question 5
1 / -0

The magnetic field in a plane electromagnetic field is given by $$B_y=2\times10^{-7} sin(0.5\times10^3z+1.5\times10^{11}t)T$$
The expression for the electric field may be given by

A
$$E_y=2\times10^{-7} sin(0.5\times10^3z+1.5\times10^{11}t)\frac{v}{m}$$

B
$$E_x=2\times10^{-7}sin(0.5\times10^3z+1.5\times10^{11}t)\frac{v}{m}$$

C
$$E_y=60sin(0.5\times10^3z+1.5\times10^{11}t)\frac{v}{m}$$

D
$$E_x=60sin(0.5\times10^3z+1.5\times10^{11}t)\frac{v}{m}$$

Solution
Question 6
1 / -0

A metal block is exposed to beams of X-ray of different wavelength. X-rays of which wavelength penetrate most?

A
$$2\overset{o}{A}$$

B
$$4\overset{o}{A}$$

C
$$6\overset{o}{A}$$

D
$$8\overset{o}{A}$$

Solution

Penetrating power is greater for lower wavelength
option A
Question 7
1 / -0

If electric field in a non-magnetic medium for EM wave is given by $$\vec{ E } =100 \sin\left( 10^ 8\quad t\quad +2z \right) \hat { j }$$ then $$\vec {H}$$ is.

A
$$ \dfrac { 50 }{ \pi } sin\left( 10^ 8\quad t\quad +\quad 2z \right) \hat { i } $$

B
$$ \dfrac { 5 }{ 6\pi } sin\left( 10^ 8\quad t\quad +\quad 2z \right) \hat { i } $$

C
$$ 20 sin\left( 10^ 8\quad t\quad +\quad 2z \right) \hat { i } $$

D
$$ \dfrac { 25 }{ \pi } sin\left( 10^ 8\quad t\quad +\quad 2z \right) \hat { j } $$

Solution
Question 8
1 / -0

The electric field of a plane electromagnetic wave is given by $$E=E_{0}\sin (kz-\omega t)[\hat i+\hat j]$$. Which of the following gives the direction of the associated magnetic field?

A
$$\hat K$$

B
$$-\hat i+\hat j$$

C
$$-\hat i-\hat j$$

D
$$\hat i-\hat j$$

Solution
Question 9
1 / -0

In Maxwell's velocity distribution curve area under the graph

A
Increases when temperature is increased

B
Deccreases when temperature is increased

C
Remains same at all temperature

D
Depends on the pressure of the gas

Solution

Area under the Maxwell's velocity distribution curve gives the number of particles. Since number of particles remains the same at all the temperatures, so the area under the curve also remains the same at all temperature.
Question 10
1 / -0

The displacement current was named as current because

A
It is similar conduction current

B
It produced a magnetic field

C
It is a time varying field

D
It is current due to uniformly moving charge

Solution