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

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:
  • $$2N/m^2$$
  • $$2\times 10^{-4}N/m^2$$
  • $$6N/m^2$$
  • $$6\times 10^{-4}N/m^2$$
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.
  • Statement 1 is true, Statement 2 is true, Statement 2 is the correct explanation of Statement 1
  • Statement 1 is false, Statement 2 is true.
  • Statement 1 is true, Statement 2 is false
  • 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
  • $$8.33\ \times { 10 }^{ -8 }\hat { k }\ T$$
  • $$18.9\ \times { 10 }^{ -8 }\hat { k }\ T$$
  • $$4.1\ \times { 10 }^{ -8 }\hat { k }\ T$$
  • $$2.1\ \times { 10 }^{ -8 }\hat { k }\ T$$
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:
  • $$10\ KV$$
  • $$20\ KV$$
  • $$30\ KV$$
  • $$40\ KV$$
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 
  • $$1.2A$$
  • 12 x $${ 10 }^{ -6 }$$A
  • 7.2 x $${ 10 }^{ -6 }$$A
  • none 
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 
  • $$550A$$
  • $$5.56 \times 10^2A$$
  • $$5.56 \times 10^3A$$
  • $$2.28 \times 10^4A$$
Minimum energy that a $$\gamma-ray$$ must have to give rise to an electron-position pair is
  • $$0.51\ MeV$$
  • $$1.02\ MeV$$
  • $$2.04\ MeV$$
  • $$1.53\ MeV$$
Wavelength of light in different media are proportional to:
  • speed of light in that medium
  • Amplitude of light in that medium
  • frequency of light in that mrdium
  • 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?
  • $$1.1 \times 10^{-4} kg ms^{-1}$$
  • $$2.7 \times 10^{-4} kg ms^{-1}$$
  • $$3.7 \times 10^{-4} kg ms^{-1}$$
  • $$3.7 \times 10^{-3} kg ms^{-1}$$
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= $$1.8\times 10^{11}C/kg$$) ?
  • 1:1
  • 1:10
  • 1:100
  • 1:1000
Which of the following electromagnetic waves have minimum frequency 
  • Microwaves
  • Audible waves
  • Ultriasonic waves
  • 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:
  • $$ H_o = E_o $$
  • $$ H_ o=\frac { E_ o }{ c } $$
  • $$ H_ o=\quad E_ o\quad \sqrt { \frac { \mu _ o }{ \varepsilon _ o } } $$
  • $$ H_ o=\quad E_ o\quad \sqrt { \frac { \varepsilon _ o }{ \mu _ o } } $$
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 
  • 1.34 V/m
  • 2.68 V/m
  • 4.02 V/m
  • 5.36 V/m
A hydrogen atom is in ground state. In order to get six lines in its emission spectrum, wavelength of incident radiation should be 
  • 800 $$\mathop A\limits^ \circ $$
  • 825 $$\mathop A\limits^ \circ $$
  • 972 $$\mathop A\limits^ \circ $$
  • 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
  • The refractive index of ionosphere becomes very high for $$f > f _ { c }$$
  • The refractive index of ionosphere becomes very low for $$f > f _ { c }$$
  • The refractive index of ionosphere becomes very high for $$f < f _ { c }$$
  • 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
  • Ultra X ray
  • Ultra scanning
  • Ultra sonography
  • None of these
The mathematical equation for magnetic field lines of force is 
  • $$\vec \nabla . \vec B = 0$$
  • $$\vec \Delta . \vec B \neq 0 1$$
  • $$\vec \nabla . \vec B > 0$$
  • $$\vec \nabla . \vec B < 0$$
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
  • $$\mathrm { E } = 100 \mu \mathrm { N } / \mathrm { C } \sin \left[ \left( 2 \times 10 ^ { 15 } \mathrm { s } ^ { - 1 } \right) ( \mathrm { t } - \mathrm { x } / \mathrm { c } ) \right] ( - \hat { \mathrm { k } } )$$
  • $$\mathrm { E } = 3 \times 10 ^ { 10 } \mu \mathrm { N } / \mathrm { Csin } \left[ \left( 2 \times 10 ^ { 15 } \mathrm { s } ^ { - 1 } \right) ( \mathrm { t } - \mathrm { x } / \mathrm { c } ) \right] ( - \hat { \mathrm { k } } )$$
  • $$\mathrm { E } = 3 \times 10 ^ { 10 } \mu \mathrm { N } / \mathrm { C } \sin \left[ \left( 2 \times 10 ^ { 15 } \mathrm { s } ^ { - 1 } \right) ( \mathrm { t } - \mathrm { x } / \mathrm { c } ) \right] \hat { \mathrm { k } }$$
  • $$\mathrm { E } = 100 \mu \mathrm { N } / \mathrm { C } \sin \left[ \left( 2 \times 10 ^ { 15 } \mathrm { s } ^ { - 1 } \right) ( \mathrm { t } - \mathrm { x } / \mathrm { c } ) \right] \mathrm { \hat k }$$
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
  • Faraday's law of induction
  • Modified Ampere's law
  • Gauss's law of electricity
  • 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:
  • $$ u(3/4)^{ \frac { 1 }{ 2 } } $$
  • $$ u(4/3)^{ \frac { 1 }{ 2 } } $$
  • less than $$ u(4/3)^{ \frac { 1 }{ 2 } } $$
  • 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 
  • Wave length doubled and frequency remains unchanged
  • Wave length doubled and frequency becomes half
  • Wave length is halved and frequency remains unchanged
  • 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 
  • $$4.4\ Wm^{-1}$$
  • $$0.44\ Wm^{-1}$$
  • $$5.65\ Wm^{-1}$$
  • $$4.0\ Wm^{-1}$$
Find the distance (in meters) traveled by a radio wave in $$5.00$$ seconds?
  • $$3\times {10}^{9}m$$
  • $$2.9\times {10}^{9}m$$
  • $$3.6\times {10}^{6}m$$
  • $$1.5\times {10}^{9}m$$
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?
  • $$9.31, 0.368, 0.773$$
  • $$1,39, 0.341, 1.66$$
  • $$1.39, 0.638, 0.337$$
  • $$None of these$$
The structure of solids is studied by
  • X-rays
  • $$\gamma-rays$$
  • Cosmic rays
  • 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 $$cm^2$$?  
  • 1.062 x $$10^{-2}$$ A
  • 2.062 x $$10^{-2}$$ A
  • 3.062 x $$10^{-2}$$ A
  • 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?
  • $$ \left( 2\hat { i } +3\hat { j } \right) and\left( \hat { i } +2\hat { j } \right) $$
  • $$ \left( -2\hat { i } -3\hat { j } \right) and\left( 3\hat { i } -2\hat { j } \right) $$
  • $$ \left( 3\hat { i } +3\hat { j } \right) and\left( 4\hat { i } -3\hat { j } \right) $$
  • $$ \left( \hat { i } +2\hat { j } \right) and\left(2 \hat { i } \hat { j } \right) $$
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 $$n=1$$)
  • $$n = 2$$ to $$n = 1$$
  • $$n = 3$$ to $$n = 1$$
  • $$n = 4$$ to $$n = 2$$
  • 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.
  • $${ \epsilon \epsilon }_{ 0 }\omega /\sigma $$
  • $$\sigma /{ \epsilon \epsilon }_{ \sigma }\omega $$
  • $$\omega /{ \sigma \epsilon }_{ 0 }\omega $$
  • $$\omega \sigma /{ \epsilon }_{ 0 }\epsilon $$
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
  • $$x$$-direction
  • $$z$$-direction
  • $$y$$-direction
  • $$xz$$ plane at an angle of $$45^0$$ between the $$x$$ and $$z$$direction
_____ light creates intense heating when it is incident on a substance
  • visible
  • ultra violet
  • Infra red
  • 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.
  • 1
  • 2
  • 3
  • 4
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.
  • 1
  • 2
  • 3
  • 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 :
  • $$\dfrac {\varepsilon \varepsilon_0 \omega} \sigma $$
  • $$\dfrac \sigma {\varepsilon \varepsilon_0 \omega}$$
  • $$\dfrac {\omega} {\sigma \varepsilon _0 \varepsilon }$$
  • $$\dfrac {\omega \sigma } {\varepsilon _0 \varepsilon }$$
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 :
  • $$ \vec { E } = E_0 \cos \left(\omega t -\dfrac{2\pi}{\lambda}y\right)\hat{x}$$
  • $$\vec{ E } = -E_0 \cos \left(\omega t +\dfrac{2\pi}{\lambda}y\right)\hat{x}$$
  • $$\vec{ E } = -E_0 \cos \left(\omega t +\dfrac{2\pi}{\lambda}y\right)\hat{z}$$
  • $$\vec { E } = E_0 \cos \left(\omega t -\dfrac{2\pi}{\lambda}y\right)\hat{z}$$
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:-
  • $$29$$
  • $$27$$
  • $$25$$
  • $$23$$
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.
  • 1
  • 2
  • 3
  • 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:
  • $$3.33\times{10}^{-5}J/{m}^{2}$$
  • $$26.5J/{m}^{2}$$
  • $$3\times{10}^{8}J/{m}^{2}$$
  • 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 
  • Will have frequency of $$10^9\, Hz.$$
  • Will have frequency of $$2\times 10^9\, Hz.$$
  • Will have wavelength of $$0.3\,m.$$
  • 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 
  • $$2$$
  • $$3$$
  • $$4$$
  • $$5$$
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 
  • $$500$$
  • $$100$$
  • $$\cfrac{500}{3}$$
  • $$\cfrac{250}{3}$$
The solar spectrum is:
  • continuous
  • line spectrum
  • spectrum of black lines
  • spectrum of black bands
If $$v_{x}$$, $$v_{i}$$ and $$v_{m}$$ are the speeds of gamma rays, X-rays and micro waves respectively in vacuum, then 
  • $$v _ { g } > v _ { x } > v _ { m }$$
  • $$v _ { x } < v _ { x } < v _ { m }$$
  • $$v _ { x } > v _ { i } < v _ { m }$$
  • $$v _ { x} = v _ { i } = v _ { m }$$
The displacement current is given by the expression
  • $$\mu_0\epsilon_0$$
  • $$\mu_0\epsilon_0\cfrac{d\phi_E}{dt}$$
  • $$\epsilon_0\cfrac{d\phi_E}{dt}$$
  • $$\mu_0\left(1+\epsilon_0\cfrac{d\phi_E}{dt}\right)$$
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  $$\left( \mu _ { air } = 1.0008 \right) .$$
  • $$0.5 \mathrm { mm }$$
  • $$1 \mathrm { mm }$$
  • $$18 \mathrm { mm }$$
  • $$24 \mathrm { mm }$$
Displacement current flows
  • Between capacitors plates and wire of circuit
  • In between capacitor plates only
  • In resistance of circuit only
  • 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
  • a, b, c
  • a, b
  • a, c
  • 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 
  • $$4.58\times{ 10 }^{ -6 }{ Jm }^{ -3 };2.15\times{ 10 }^{ -7 }{ Jm }^{ -3 }$$
  • $$4.3\times{ 10 }^{ -7 }{ Jm }^{ -3 };8.6\times{ 10 }^{ -7 }{ Jm }^{ -3 }$$
  • $$2.15\times{ 10 }^{ -7 }{ Jm }^{ -3 };4.3\times{ 10 }^{ -7 }{ Jm }^{ -3 }$$
  • $$8.6\times{ 10 }^{ -7 }{ Jm }^{ -3 };4.3\times{ 10 }^{ -7 }{ Jm }^{ -3 }$$
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 = $$3\times { 10 }^{ 8 }m{ s }^{ -1 }$$)
  • 15.3 GHz
  • 10.1 GHz
  • 12.1 GHz
  • 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
  • Both A and B are true
  • A is false but B is true
  • B is false but A is true
  • Both A and B are false
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