Tag: physics

Questions Related to physics

An electromagnetic wave with frequency $\omega$ and wavelength $\lambda$ travels in the $+y$ direction. Its magnetic field is along $-x$ axis. The vector equation for the associated electric field (of amplitude E_0)is :

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. $ \vec { E } = E _0 \cos \left(\omega t -\dfrac{2\pi}{\lambda}y\right)\hat{x}$

  2. $\vec{ E } = -E _0 \cos \left(\omega t +\dfrac{2\pi}{\lambda}y\right)\hat{x}$

  3. $-\vec{ E } = E _0 \cos \left(\omega t +\dfrac{2\pi}{\lambda}y\right)\hat{z}$

  4. $\vec { E } = E _0 \cos \left(\omega t -\dfrac{2\pi}{\lambda}y\right)\hat{z}$

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Correct Option: A

Electro magnetic waves are transverse in nature as is evident by

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. polarization

  2. interference

  3. reflection

  4. deffraction

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Correct Option: A
Explanation:

Electromagnetic waves are transverse in nature as is evident by polarization interference and diffraction explain the wave nature of light or $EM$ waves polarization is the phenomenon by which we restrict the vibration of wave in a particular direction perpendicular to direction of $W$ are propagation. So, it explains the transverse nature of $EM$ waves.

Answer :- polarization.

The maximum kinetic energy of electron if wavelength of incident electromagnetic wave is $260 \,nm$ and cut-off wavelength is $380 \,nm$ given $hc = 1237 \,nm-eV$ is

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. $1.5 \,eV$

  2. $6.4 \,eV$

  3. $10 \,eV$

  4. None of these

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Correct Option: A
Explanation:

We know 
$KE _{max} = \dfrac{hc}{\lambda} - \dfrac{hc}{\lambda _0} $
$= \dfrac{1237 \, nm. eV}{260 \, nm} - \dfrac{1237 \, nm . eV}{380 \, nm}$
$= 1.5 eV$

If $\vec{E} = E _0 \cos (kz) \cos (\omega t)\hat{i}$ then $\vec{B}$ for electromagnetic wave is:

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. $\vec{B} = \dfrac{E _0}{C} \hat{k}$

  2. $\vec{B} = \dfrac{E _0}{C} \sin (kz) \sin (\omega t)\hat{i}$

  3. $\vec{B} = \dfrac{E _0}{C} \sin (kz) \cos (\omega t) \hat{j}$

  4. $\vec{B} = \dfrac{E _0}{C} \cos (kz) \sin (\omega t) \hat{j}$

Show answer
Correct Option: B
Explanation:

$\dfrac{dE}{dz} = -\dfrac{dB}{dt}$
If $\vec{E} = E _0 \, \cos (kz) \cos (\omega t)$ then
$\vec{B} = \dfrac{E _0}{C} \sin (kz) \sin (\omega t)$ will satisfy the equation

For the propagation of electromagnetic waves

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. Medium is required

  2. no medium is required

  3. E and B are in mutually opposite phase

  4. E and b do not contriute

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Correct Option: B
Explanation:

Electromagnetic waves are a result of changing electric field creating magnetic field and the magnetic field does the same for electric field. Unlike mechanical waves, electromagnetic waves does not require material medium to transfer energy from one place to another.

On the basis of the following features identify correct option:
I. They require no material medium.
II. They are always transverse.
II. They are produced by accelerating charged particles

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. Mechanical waves

  2. Electro-magnetic waves

  3. Both (1) and (2)

  4. Neither (1) and (2)

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Correct Option: B
Explanation:

Electromagnetic waves do not need any material medium for their propagation and they are always transverse in nature e.g. light waves.

A long spring is fixed at one end. A person holding the other end compresses the spring with a jerk. The compression travels along the length of the spring. Which kind of wave is travelled along the length of the spring?

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. Electromagnetic waves

  2. Transverse waves

  3. Longitudinal waves

  4. Both (A) and (C)

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Correct Option: C
Explanation:

If the spring is compressed, particles of the spring come close and there is compression.When spring is extended, particles rarefact from each other . Direction of particle motion is in the direction of wave propagation, Hence longitudinal waves  .


In which of the following media can non-mechanical waves travel?

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. In vacuum as well as in a medium

  2. In vacuum but not in a medium

  3. In a medium but not in a vacuum

  4. Neither in a medium nor in vacuum

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Correct Option: A
Explanation:

Non mechanical waves are waves that do not require a medium for transfer of their energy to occur electromagnetic waves are the only type of non mechanical waves.

Non mechanical waves can travel both in vacuum or in any medium

Which of the following have zero average value in a plane electromagnetic wave?
(i) Magnetic field
(ii) Electric field
(iii) Electric energy
(iv) Magnetic energy.

the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

  1. (i) and (ii)

  2. (i) and (iv)

  3. (ii) and (iii)

  4. (iii) and (iv)

Show answer
Correct Option: A
Explanation:

Electric field has zero average value in electromagnetic waves

Choose the correct answer from the alternatives given.
The charge on a parallel plate capacitor varies as $q \, = \, q _0 \, cos2\pi \nu t$. The plates are very large and close together (area = A, separation = d). The displacement current through the capacitor is then

parallel plate capacitor electrostatic potential and capacitance electrostatics physics

  1. $3q _0 \, 2\pi \nu \, sin2\pi \nu t$

  2. $-q _0 \, 2\pi \nu \, sin2\pi \nu t$

  3. $4q _0 \, 2\pi \, sin2\pi \nu t$

  4. $5q _0 \, 2\pi \, sin2\pi \nu t$

Show answer
Correct Option: B
Explanation:

Given: The charge on the parallel plate capacitor varies as $q=q _0cos2\pi\nu t$


To find: The displacement current through the capacitor.

The displacement current in a capacitor is equal to the conduction current of the capacitor.
Displacement current, $I _D \, =I _C$


The conduction current in a capacitor is given by:
$I _C= \dfrac{dq}{dt}$
$\implies\, \dfrac{d}{dt} \, [q _0 \, cos \, 2\pi\nu t]$

$  \,=\, -q _0 \, 2\pi \nu\, sin2\pi \nu\,t$


Option $(B)$ is correct.