Tag: physics

Quizzes (598) Questions (13441)

Questions Related to physics

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

  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. $\vec { E } = E _0 \cos \left(\omega t -\dfrac{2\pi}{\lambda}y\right)\hat{z}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice the nature of electromagnetic waves space exploration and forms of light observing space: telescopes electromagnetic waves physics

Electro magnetic waves are transverse in nature as is evident by

  1. polarization

  2. interference

  3. reflection

  4. deffraction
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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

  1. $1.5 \,eV$

  2. $6.4 \,eV$

  3. $10 \,eV$

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

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

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

  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. $\vec{B} = \dfrac{E _0}{C} \cos (kz) \sin (\omega t) \hat{j}$
Reveal answer Fill a bubble to check yourself
B Correct answer
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

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

For the propagation of electromagnetic waves

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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

  1. Mechanical waves

  2. Electro-magnetic waves

  3. Both (1) and (2)

  4. Neither (1) and (2)
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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

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

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?

  1. Electromagnetic waves

  2. Transverse waves

  3. Longitudinal waves

  4. Both (A) and (C)
Reveal answer Fill a bubble to check yourself
C Correct answer
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  .


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

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

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
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

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

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.

  1. (i) and (ii)

  2. (i) and (iv)

  3. (ii) and (iii)

  4. (iii) and (iv)
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Electric field has zero average value in electromagnetic waves

Multiple choice parallel plate capacitor electrostatic potential and capacitance electrostatics physics

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

  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. $5q _0 \, 2\pi \, sin2\pi \nu t$
Reveal answer Fill a bubble to check yourself
B Correct answer
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.