MCQ Questions for Class 12 Medical Physics Electromagnetic Waves Quiz 11

Light with an energy flux of

$18 W/cm^2$ falls on a non-reflecting surface at normal incidence. The pressure exerted on the surface is:

0%
$2N/m^2$
0%
$2\times 10^{-4}N/m^2$
0%
$6N/m^2$
0%
$6\times 10^{-4}N/m^2$

Explanation

Pressure exerted on the surface

$P=\dfrac{F}{A}$

Momentum

$p=\dfrac{E}{c}$

where E is the energy of incident light, c is the speed of light.

Thus

$P=\dfrac{1}{c}(\dfrac{1}{A}\dfrac{dE}{dt})$

$=\dfrac{Flux}{c}$

$=\dfrac{18\times 10^{4}}{3\times 10^8}=6\times 10^{-4}N/m^2$

This question has Statement-1 and Statement-2, Of the four choice given after the statements choose the one that best describes the two statements.
Statements-1: Out of the radio waves and microwaves. the radio waves undergo more diffraction.
Statement-2: Radio waves have greater frequency compared to microwaves.

0%
Statement 1 is true, Statement 2 is true, Statement 2 is the correct explanation of Statement 1
0%
Statement 1 is false, Statement 2 is true.
0%
Statement 1 is true, Statement 2 is false
0%
Statement 1 is true, Statement 2 is true, Statement 2 is not the correct explanation of Statement-1

A plane electromagnetic wave of frequency 50 MHz travels in free space along the x-direction . At a particular point in space and time,

$\overrightarrow { E }$ = 6.3

$\hat j$ V

${m}^{-1}$ . At this point

$\overrightarrow { B }$ is equal to

0%
$8.33\ \times { 10 }^{ -8 }\hat { k }\ T$
0%
$18.9\ \times { 10 }^{ -8 }\hat { k }\ T$
0%
$4.1\ \times { 10 }^{ -8 }\hat { k }\ T$
0%
$2.1\ \times { 10 }^{ -8 }\hat { k }\ T$

Explanation

Given: The Electric field intensity due to electromagnetic waves is,

$E_0=6.3\ V/m$

To find: The direction and intensity of the magnetic field of Electromagnetic wave.

The magnetic field intensity due to the wave is given by

$B_0=\dfrac{E_0}{C}$

$\Rightarrow B_0=\dfrac{6.3}{3\times 10^8}=2.1\times 10^{-8}$ Tesla

Since the propagation of the wave is along

$\hat i$ (X-direction) and the electric field vector is along

$\hat j$ , the magnetic field of the wave should lie perpendicular to both the direction of propagation and direction of electric field.

So,

$\vec B$ should be along

$\vec k$ such that

$\vec E\times \vec B$ should give

$\hat i$ ( propagation in X-direction).

$\Rightarrow \vec B=B_0\hat k$

$\vec B=2.1\times 10^{-8}\ T\ \hat k$

A beam of electrons accelerated by a large potential difference

$V$ is made to strike a metal target to produce

$X-$ rays. For which of the following values of

$V$ , the resulting

$X-$ rays have the lowest minimum wave length:

0%
$10\ KV$
0%
$20\ KV$
0%
$30\ KV$
0%
$40\ KV$

Explanation

As we know,

$\boxed{E_{max}=\dfrac{hc}{\lambda_{min}}}$

$\boxed{\lambda_{min}=\dfrac{hc}{ev}}$

Here the value of

$v$ is given as

$10kv,20kv,30kv,40kv$

$\boxed{\lambda \propto \dfrac{1}{V}}$ , large value of

$V$

$\Rightarrow$ min. value of

$\lambda$

Hence for

$40kv$ ,

$\lambda_{min}$ is minimum.

$\therefore$ option

$D$ is correct.

Potential difference across plates of a capacitor

$6\mu F$ is changing at the rate of

$72V{ s }^{ -1 }$ . Displacement current at that instant will be

0%
$1.2A$
0%
12 x ${ 10 }^{ -6 }$ A
0%
7.2 x ${ 10 }^{ -6 }$ A
0%
none

Explanation

Given,

$C=\dfrac{A\varepsilon_0}{d}=6\mu C$

$\dfrac{dV}{dt}=72V/s$

Displacement current,

$I_D=\varepsilon_0 \dfrac{d\phi_E}{dt}$

$I_D=\varepsilon_0\dfrac{d(EA)}{dt}$

$I_D=\varepsilon_0 A\dfrac{d(V/d)}{dt}$

$I_D=\dfrac{\varepsilon_0 A}{d}.\dfrac{dV}{dt}$

$I_D=C\dfrac{dV}{dt}$

$I_D=6\times 10^{-6}\times 72$

$I_D=432\times 10^{-6}A$

The correct option is D.

A parallel late condenser consists of two circular plate each of radius

$2cm$ separated by a distance of

$0.1mm$ . A time varying potential difference of

$5\times 10^{13}v/s$ is applied across the plated of the condenser: The displacement current is

0%
$550A$
0%
$5.56 \times 10^2A$
0%
$5.56 \times 10^3A$
0%
$2.28 \times 10^4A$

Minimum energy that a

$\gamma-ray$ must have to give rise to an electron-position pair is

0%
$0.51\ MeV$
0%
$1.02\ MeV$
0%
$2.04\ MeV$
0%
$1.53\ MeV$

Wavelength of light in different media are proportional to:

0%
speed of light in that medium
0%
Amplitude of light in that medium
0%
frequency of light in that mrdium
0%
Nove of above

A plane electromagnetic wave with an intensity of

$200 W/m^2$ is incident normal to a flat plate of radius 30 cm. If the plate absorbs

$60\%$ and reflects

$40\%$ of the incident radiation, what is the momentum transferred to it in 5 min?

0%
$1.1 \times 10^{-4} kg ms^{-1}$
0%
$2.7 \times 10^{-4} kg ms^{-1}$
0%
$3.7 \times 10^{-4} kg ms^{-1}$
0%
$3.7 \times 10^{-3} kg ms^{-1}$

A potential difference of 0.1kV is applied across an X-ray tube. The ratio of the de-Broglie wave lengths of incident electron, striking the target to the shortest wavelength of X-rays produced nearly (e/m of electron=

$1.8\times 10^{11}C/kg$ ) ?

0%
1:1
0%
1:10
0%
1:100
0%
1:1000

Which of the following electromagnetic waves have minimum frequency

0%
Microwaves
0%
Audible waves
0%
Ultriasonic waves
0%
Radiowaves

In the EM wave , the amplitude of magnetic field

$H_o$ and the amplitude of electric field

$E_o$ at a place D are related as:

0%
$H_o = E_o$
0%
$H_ o=\frac { E_ o }{ c }$
0%
$H_ o=\quad E_ o\quad \sqrt { \frac { \mu _ o }{ \varepsilon _ o } }$
0%
$H_ o=\quad E_ o\quad \sqrt { \frac { \varepsilon _ o }{ \mu _ o } }$

A lamp emits monochromatic green light uniformly in all directions. the lamp is

$3$ % in converting electrical power to electromagnetic waves and consumes

$100 W$ of power. The amplitude of the electric field associated with the electromagnetic radiation at a distance of

$10 m$ from the lamp will nearly

0%
1.34 V/m
0%
2.68 V/m
0%
4.02 V/m
0%
5.36 V/m

Explanation

$\textbf {Hint :}$ Use intensity

$I = \dfrac{P}{4\pi R^2}$ and

$I = \dfrac{1}{2} \epsilon c E^2$

$\textbf{Step 1: }$ Calculating Intensity

Given power of EM waves =

$3\%\ of\ 100w = 3w$

distance

$R=10m$

$I = \dfrac{P}{4\pi R^2}$

$\Rightarrow$

$I = \dfrac{3w}{4\pi 10^2}=0.0024\ w/m^2$

$\textbf{Step 2: }$ Calculating electric field

$I = \dfrac{1}{2} \epsilon c E^2$

$\Rightarrow$

$0.0024 = \dfrac{1}{2}\times 8.85\times 10^{-12}\times 3\times 10^8\times E^2$

$\Rightarrow$

$E = 1.34\ V/m$

Hence the electromagnetic radiation is

$1.34\ V/m$

${\textbf{Correct option: A}}$

A hydrogen atom is in ground state. In order to get six lines in its emission spectrum, wavelength of incident radiation should be

0%
800 $\mathop A\limits^ \circ$
0%
825 $\mathop A\limits^ \circ$
0%
972 $\mathop A\limits^ \circ$
0%
1025 $\mathop A\limits^ \circ$

Electromagnetic wave with frequencies greater than the critical frequency of ionosphere cannot be used for communication using sky wave propagation because

0%
The refractive index of ionosphere becomes very high for $f > f _ { c }$
0%
The refractive index of ionosphere becomes very low for $f > f _ { c }$
0%
The refractive index of ionosphere becomes very high for $f < f _ { c }$
0%
The refractive index of ionosphere becomes very low for $f < f _ { c }$

Ultra sound wave used to scan the internal organs of the body is

0%
Ultra X ray
0%
Ultra scanning
0%
Ultra sonography
0%
None of these

The mathematical equation for magnetic field lines of force is

0%
$\vec \nabla . \vec B = 0$
0%
$\vec \Delta . \vec B \neq 0 1$
0%
$\vec \nabla . \vec B > 0$
0%
$\vec \nabla . \vec B < 0$

The magnetic field in a plane EM wave is given by -

$\mathrm { B } = ( 100 \mu \mathrm { T } ) \sin \left[ \left( 2 \times 10 ^ { 15 } \mathrm { S } ^ { - 1 } \right) ( \mathrm { t } - \mathrm { x } / \mathrm { c } ) \right] \hat { \mathrm { j } }$
The equation for electric field is

0%
$\mathrm { E } = 100 \mu \mathrm { N } / \mathrm { C } \sin \left[ \left( 2 \times 10 ^ { 15 } \mathrm { s } ^ { - 1 } \right) ( \mathrm { t } - \mathrm { x } / \mathrm { c } ) \right] ( - \hat { \mathrm { k } } )$
0%
$\mathrm { E } = 3 \times 10 ^ { 10 } \mu \mathrm { N } / \mathrm { Csin } \left[ \left( 2 \times 10 ^ { 15 } \mathrm { s } ^ { - 1 } \right) ( \mathrm { t } - \mathrm { x } / \mathrm { c } ) \right] ( - \hat { \mathrm { k } } )$
0%
$\mathrm { E } = 3 \times 10 ^ { 10 } \mu \mathrm { N } / \mathrm { C } \sin \left[ \left( 2 \times 10 ^ { 15 } \mathrm { s } ^ { - 1 } \right) ( \mathrm { t } - \mathrm { x } / \mathrm { c } ) \right] \hat { \mathrm { k } }$
0%
$\mathrm { E } = 100 \mu \mathrm { N } / \mathrm { C } \sin \left[ \left( 2 \times 10 ^ { 15 } \mathrm { s } ^ { - 1 } \right) ( \mathrm { t } - \mathrm { x } / \mathrm { c } ) \right] \mathrm { \hat k }$

The Maxwell's equation :

$\oint \vec { \mathrm { B } }$ .

$\vec { \mathrm { d } l } = \mu _ { 0 } \left( \mathrm { i } + \varepsilon _ { 0 } \cdot \frac { \mathrm { d } \phi _ { \mathrm { E } } } { \mathrm { dt } } \right)$ is a statement of

0%
Faraday's law of induction
0%
Modified Ampere's law
0%
Gauss's law of electricity
0%
Gauss's law of magnetism

On photo-emissive cell, with exciting wavelength I, the fastest electron has speed u. If the exciting wavelength is changed to 3I/4, the speed of the fastest emitted electron will be:

0%
$u(3/4)^{ \frac { 1 }{ 2 } }$
0%
$u(4/3)^{ \frac { 1 }{ 2 } }$
0%
less than $u(4/3)^{ \frac { 1 }{ 2 } }$
0%
Greater than $u(4/3)^{ \frac { 1 }{ 2 } }$

An electro magnetic wave of frequency 3 MHz passes from Vacuum into a dielectric medium with permittivity

$\epsilon = 4.0$ Then

0%
Wave length doubled and frequency remains unchanged
0%
Wave length doubled and frequency becomes half
0%
Wave length is halved and frequency remains unchanged
0%
Wave length and and frequency both remain unchanged

In an electromagnetic wave in vacuum. The electrical and magnetic fields are

$40 \pi\ V/m$ and

$0.4\times 10^{-7}T$ . The pointing vector

0%
$4.4\ Wm^{-1}$
0%
$0.44\ Wm^{-1}$
0%
$5.65\ Wm^{-1}$
0%
$4.0\ Wm^{-1}$

Find the distance (in meters) traveled by a radio wave in

$5.00$ seconds?

0%
$3\times {10}^{9}m$
0%
$2.9\times {10}^{9}m$
0%
$3.6\times {10}^{6}m$
0%
$1.5\times {10}^{9}m$

A standard radio broadcasting station has an assigned frequency between

$535$ and

$1605\ kHz$ . The VHF(very high frequency) television stations (channels

$2$ to

$13$ ) have frequencies between

$54$ and

$216\ MHz$ , while the UHF (u=ultra) stations (channels

$14$ to

$83$ ) have frequencies between

$470$ and

$890\ MHz$ . What is the wavelength corresponding to each of the frequencies mentioned?

0%
$9.31, 0.368, 0.773$
0%
$1,39, 0.341, 1.66$
0%
$1.39, 0.638, 0.337$
0%
$None of these$

The structure of solids is studied by

0%
X-rays
0%
$\gamma-rays$
0%
Cosmic rays
0%
Infrared rays

A parallel plate capacitor of plate separation 2 mm is connected in an electric circuit having source voltageWhat is the value of the displacement current for

$10^{-6}$ s, if plate area is 60

$cm^2$ ?

0%
1.062 x $10^{-2}$ A
0%
2.062 x $10^{-2}$ A
0%
3.062 x $10^{-2}$ A
0%
5.062 x $10^{-2}$ A

For plane electromagnetic waves propagating in the positive Z direction, Which one of the following combination gives the correct possible direction of

$\xrightarrow [ E ]{ } abd\xrightarrow [ B ]{ }$ field respectively?

0%
$\left( 2\hat { i } +3\hat { j } \right) and\left( \hat { i } +2\hat { j } \right)$
0%
$\left( -2\hat { i } -3\hat { j } \right) and\left( 3\hat { i } -2\hat { j } \right)$
0%
$\left( 3\hat { i } +3\hat { j } \right) and\left( 4\hat { i } -3\hat { j } \right)$
0%
$\left( \hat { i } +2\hat { j } \right) and\left(2 \hat { i } \hat { j } \right)$

Neglecting reduced mass effects, what optical transition in the

${ He }^{ + }$ spectrum would have the same wavelength as the first Lyman transition of hydrogen (

$n=2$ to

$n=1$ )

0%
$n = 2$ to $n = 1$
0%
$n = 3$ to $n = 1$
0%
$n = 4$ to $n = 2$
0%
None of the above

A plane electromagnetic wave of angular frequency

${ mm }^{ 2 }$ propagates in a poorly conducting medium of conductivity

$\sigma$ and relative permittivity

$\epsilon$ Find the ratio of conduction current density and displacement current density in the medium.

0%
${ \epsilon \epsilon }_{ 0 }\omega /\sigma$
0%
$\sigma /{ \epsilon \epsilon }_{ \sigma }\omega$
0%
$\omega /{ \sigma \epsilon }_{ 0 }\omega$
0%
$\omega \sigma /{ \epsilon }_{ 0 }\epsilon$

If a plane electromagnetic wave satisfies the equation

$\dfrac{\partial ^2E_x}{\partial^2z}= C^2 \dfrac{\partial^2E_x}{\partial^2t},$ the wave propagates in

0%
$x$ -direction
0%
$z$ -direction
0%
$y$ -direction
0%
$xz$ plane at an angle of $45^0$ between the $x$ and $z$ direction

_____ light creates intense heating when it is incident on a substance

0%
visible
0%
ultra violet
0%
Infra red
0%
X-ray

A gas of identical hydrogen like atoms has some atoms in ground state and some atoms in a particular excited state and there are no atoms in any other energy level. The atoms of the gas make transition to a higher state by absorbing monochromatic light of wavelength

$304 \mathring A$ . subsequently, the atoms emit radiation of only six different photon energies. Some of emitted photons have wavelength

$304 \mathring A$ , some have wavelength more and some have less than

$304 \mathring A$ ( Take

$hc = 12420 eV - \mathring A$ ). Find the principal quantum number of the initially excited state.

0%
1
0%
2
0%
3
0%
4

$304 \mathring A$ . subsequently, the atoms emit radiation of only six different photon energies. Some of emitted photons have wavelength

$304 \mathring A$ , some have wavelength more and some have less than

$304 \mathring A$ ( Take

$hc = 12420 eV - \mathring A$ ). Find the principal quantum number of the initially excited state.

0%
1
0%
2
0%
3
0%
4

A plane electromagnetic wave of angular frequency

$\omega$ propagates in a poorly conducting medium

of conductivity

$\sigma$ and relative permittivity

$\varepsilon$ . The ratio of maximum values of conduction current density and displacement current density in the medium is :

0%
$\dfrac {\varepsilon \varepsilon_0 \omega} \sigma$
0%
$\dfrac \sigma {\varepsilon \varepsilon_0 \omega}$
0%
$\dfrac {\omega} {\sigma \varepsilon _0 \varepsilon }$
0%
$\dfrac {\omega \sigma } {\varepsilon _0 \varepsilon }$

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 :

0%
$\vec { E } = E_0 \cos \left(\omega t -\dfrac{2\pi}{\lambda}y\right)\hat{x}$
0%
$\vec{ E } = -E_0 \cos \left(\omega t +\dfrac{2\pi}{\lambda}y\right)\hat{x}$
0%
$\vec{ E } = -E_0 \cos \left(\omega t +\dfrac{2\pi}{\lambda}y\right)\hat{z}$
0%
$\vec { E } = E_0 \cos \left(\omega t -\dfrac{2\pi}{\lambda}y\right)\hat{z}$

When accelerating voltage is increased from

$10\ kV$ to

$20\ kV$ in an X-ray tube, the gap between the wavelengths of

$K_{\alpha}$ line and lowest end of continuous spectrum increases three times. The atomic number of the target element is:-

0%
$29$
0%
$27$
0%
$25$
0%
$23$

$304 \mathring A$ . subsequently, the atoms emit radiation of only six different photon energies. Some of emitted photons have wavelength

$304 \mathring A$ , some have wavelength more and some have less than

$304 \mathring A$ ( Take

$hc = 12420 eV - \mathring A$ )
Find the principal quantum number of the initially excited state.

0%
1
0%
2
0%
3
0%
4

For any EM wave if

$E=100V/m$ and

$B=3.33\times{10}^{-7}T$ , then rate of energy flow per unit area is:

0%
$3.33\times{10}^{-5}J/{m}^{2}$
0%
$26.5J/{m}^{2}$
0%
$3\times{10}^{8}J/{m}^{2}$
0%
None

Which among the four options is not correct ion given situation ? A charged particle oscillates about its mean equilibrium position with a frequency of

$10^9\, Hz.$ The electromagnetic waves produced

0%
Will have frequency of $10^9\, Hz.$
0%
Will have frequency of $2\times 10^9\, Hz.$
0%
Will have wavelength of $0.3\,m.$
0%
Fall in the region of radio waves

The ionization potential of hydrogen is

$13.6 V$ . It is excited by a photon of energy

$12.1 eV$ , then the number of lines in the emission spectrum is

0%
$2$
0%
$3$
0%
$4$
0%
$5$

A point source of electromagnetic radiation has an average power output of

$1500W$ . The maximum value of electric field at a distance of

$3m$ from this source in

$V{m}^{-1}$ is

0%
$500$
0%
$100$
0%
$\cfrac{500}{3}$
0%
$\cfrac{250}{3}$

The solar spectrum is:

0%
continuous
0%
line spectrum
0%
spectrum of black lines
0%
spectrum of black bands

$v_{x}$ ,

$v_{i}$ and

$v_{m}$ are the speeds of gamma rays, X-rays and micro waves respectively in vacuum, then

0%
$v _ { g } > v _ { x } > v _ { m }$
0%
$v _ { x } < v _ { x } < v _ { m }$
0%
$v _ { x } > v _ { i } < v _ { m }$
0%
$v _ { x} = v _ { i } = v _ { m }$

The displacement current is given by the expression

0%
$\mu_0\epsilon_0$
0%
$\mu_0\epsilon_0\cfrac{d\phi_E}{dt}$
0%
$\epsilon_0\cfrac{d\phi_E}{dt}$
0%
$\mu_0\left(1+\epsilon_0\cfrac{d\phi_E}{dt}\right)$

When light of wavelength

$4000A ^ { \circ }$ in vacuum travels through the same thickness in air and vacuum the difference in the number of waves is one. Find the thickness

$\left( \mu _ { air } = 1.0008 \right) .$

0%
$0.5 \mathrm { mm }$
0%
$1 \mathrm { mm }$
0%
$18 \mathrm { mm }$
0%
$24 \mathrm { mm }$

Displacement current flows

0%
Between capacitors plates and wire of circuit
0%
In between capacitor plates only
0%
In resistance of circuit only
0%
none of these

Displacement current goes through the gap between the plates of a capacitor when the charge of the capacitor :-
(a) Increases
(b) Decreases
(c) Does not change
(d) Is zero

0%
a, b, c
0%
a, b
0%
a, c
0%
a, b, c, d

The rms value of the electric filed of a plane electromagnetic wave is 720 V/m.The average energy density of electric field and the average energy density are

0%
$4.58\times{ 10 }^{ -6 }{ Jm }^{ -3 };2.15\times{ 10 }^{ -7 }{ Jm }^{ -3 }$
0%
$4.3\times{ 10 }^{ -7 }{ Jm }^{ -3 };8.6\times{ 10 }^{ -7 }{ Jm }^{ -3 }$
0%
$2.15\times{ 10 }^{ -7 }{ Jm }^{ -3 };4.3\times{ 10 }^{ -7 }{ Jm }^{ -3 }$
0%
$8.6\times{ 10 }^{ -7 }{ Jm }^{ -3 };4.3\times{ 10 }^{ -7 }{ Jm }^{ -3 }$

An observer is moving with half the speed of light towards a stationary microwave source emitting waves at frequency 10 GHz. What is the frequency of the microwave by the observer ?(speed of light =

$3\times { 10 }^{ 8 }m{ s }^{ -1 }$ )

0%
15.3 GHz
0%
10.1 GHz
0%
12.1 GHz
0%
17.3 GHz

Consider the following two statements regarding a linearly polarized plane electromagnetic wave
(A) The electric field and the magnetic filed have equal average values
(B) The electric energy and the magnetic energy have equal average values

0%
Both A and B are true
0%
A is false but B is true
0%
B is false but A is true
0%
Both A and B are false

CBSE Questions for Class 12 Medical Physics Electromagnetic Waves Quiz 11 - MCQExams.com

0:0:1

Practice Class 12 Medical Physics Quiz Questions and Answers

CBSE Questions for Class 12 Medical Physics Electromagnetic Waves Quiz 11 - MCQExams.com

0:0:1

Practice Class 12 Medical Physics Quiz Questions and Answers

Support mcqexams.com by disabling your adblocker.