CBSE Questions for Class 12 Medical Physics Electromagnetic Waves Quiz 10 - MCQExams.com

The spectra of radiation emitted by two distant stars are shown below.
The ratio of the surface temperature of star $$A$$ to that of star $$B, T_A: T_B$$, is approximately :

1738939_282597e2613549ccb24b77e293913d0f.png
  • $$2:1$$
  • $$4:1$$
  • $$1:2$$
  • $$1:1$$
Ultrasonic are not used in : 
  • SONAR
  • Sibigraphy
  • CUSA
  • radio waves
At $$0^oC$$ body emits :
  • no radiation
  • electromagnetic radiation of single wavelength
  • electromagnetic radiation of all wavelengths that are emitted by it at room temperature
  • electromagnetic radiation of fewer wavelengths than are emitted by it at room temperature
X-rays are produced due to
  • Bombarding of electrons on solids
  • Bombarding of $$\alpha$$ -particle on solids
  • Bombarding of $$\gamma$$ -rays on solids
  • Bombarding of neutron on solids
Write true or false for the following statements :
In order to find the force experienced by a current carrying conductor , we can use Maxwell's cork screw rule. 
  • True
  • False
The source of electromagnetic waves can be a charge
  • moving with a constant velocity
  • moving in a circular orbit
  • at rest
  • falling in an electric field
In a dark room of photography, generally red light is used. The reason is
  • Most of the photographic films are not red light
  • The frequency for red light is low and hence the energy $$hv$$ of photons is less
  • (a) and (b) both
  • None of these
For the production of X-ray of wavelength $$0.1\ A^o$$ the minimum potential difference will be
  • $$12.4\ kV$$
  • $$24.8\ kV$$
  • $$124\ kV$$
  • $$248\ kV$$
A wavelength $$ 0.60 \mathrm{cm} $$ is produced in air and it travels at a speed of $$ 300  \mathrm{ms} $$. lt will be an
  • Audible wave
  • Infrasonic wave
  • Ultrasonic wave
  • None of the above
A micro-wave and an ultrasonic sound wave have the same wavelength. Their frequencies are in the ratio (approximately)
  • $$10^6 :1$$
  • $$10^2:1$$
  • $$10^4:1$$
  • $$10:1$$
For the production of characteristic $$K_{\gamma, X-}$$ ray, the electron transition is
  • $$n=2$$ to $$n=1$$
  • $$n=3$$ to $$n=2$$
  • $$n=3$$ to $$n=1$$
  • $$n=4$$ to $$n=1$$
The waves used in telecommunication are
  • $$IR$$
  • $$UV$$
  • Microwaves
  • Cosmic rays
Which of the following waves have the maximum wavelength 
  • $$X-$$ rays
  • I.R. rays
  • UV rays
  • Radio waves
Which of the following shows green house effect 
  • Ultraviolet rays
  • Infrared rays
  • $$X$$- rays
  • None of these
Radio wave diffract around building although light waves do not. The reason is that radio waves 
  • Travel with speed larger than $$c$$
  • Have much larger wavelength than light
  • Carry news
  • Are not electromagnetic waves
Which rays are not the portion of electromagnetic spectrum 
  • $$X-$$ rays
  • Microwaves
  • $$\alpha$$- rays
  • Radio waves
Electromagnetic radiation of highest frequency is 
  • Infrared radiations
  • Visible radiation
  • Radio waves
  • $$\gamma$$- rays
The electromagnetic waves travel with a velocity 
  • Equal to velocity of sound
  • Equal to velocity of light
  • Less than velocity of light
  • None of these
The frequencies of $$X-$$ rays, $$\gamma$$- rays and ultraviolet rays are respectively $$a, b$$ and $$c$$. Then 
  • $$a < b, b > c$$
  • $$a > b, b > c$$
  • $$a > b, b < c$$
  • $$a < b, b < c$$
Which of the following rays has the maximum frequency 
  • Gamma rays
  • Blue light
  • Infrared rays
  • Ultraviolet rays
Heat radiations propagate with the speed of 
  • $$\alpha$$- rays
  • $$\beta$$- rays
  • Light waves
  • Sound waves
The wavelength $$21\ cm$$ emitted by atomic hydrogen in interstellar space belongs to 
  • Radio waves
  • Infrared waves
  • Microwaves
  • $$\gamma$$- rays
Which one of the following have minimum wavelength 
  • Ultraviolet rays
  • Cosmic rays
  • $$X-$$ rays
  • $$\gamma-$$ rays
TV waves have a wavelength range of $$1-10$$ meter. Their frequency range in $$MHz$$ is 
  • $$30-300$$
  • $$3-30$$
  • $$300-3000$$
  • $$3-3000$$
If $$\lambda_v , \lambda_r $$ and $$\lambda_m$$ represent the wavelength of visible light $$x-$$ rays and microwaves respectively, then 
  • $$\lambda_m > \lambda_x > \lambda_v$$
  • $$\lambda_v > \lambda_m > \lambda_y$$
  • $$\lambda_m > \lambda_v > \lambda_v$$
  • $$\lambda_v > \lambda_x > \lambda_m$$
Which of the following electromagnetic waves?
  • $$\alpha$$ rays
  • $$\beta$$ rays
  • $$\gamma$$ rays
  • Cathode rays
Which radiation has least wavelenght?
  • $$X-ray$$
  • $$Y-ray$$
  • $$\beta-ray$$
  • $$\alpha-ray$$
A parallel plate capacitor with plate are $$A$$ and seperation between the plates $$d,$$ is charged byb a constant current $$i,$$ consider a plane surface of area $$A/2$$ parallel to the plates and drawn symmetrically between the plates, the displacement current through this area, will be.
  • $$i$$
  • $$\dfrac{i}{2}$$
  • $$\dfrac{i}{4}$$
  • None of these
Waves related to telecommunication are
  • infrared
  • visible light
  • microwaves
  • ultraviolet ray
Rank the following kinds of waves according to their wavelength ranges from those with the largest typical or average wavelength to the smallest, noting any cases of equality:
  • gamma rays
  • microwaves
  • radio waves
  • visible light
  • x-rays
A plane electromagnetic wave with a single frequency moves in vacuum in the positive $$x$$ direction. Its amplitude is uniform over the $$yz$$ plane  its wavelength,
  • increase
  • decrease
  • same
  • none
A plane electromagnetic wave with a single frequency moves in vacuum in the positive x direction. Its amplitude is uniform over the yz plane. its speed,
  • increase
  • decrease
  • stay constant
  • None of these
A plane electromagnetic wave with a single frequency moves in vacuum in the positive $$x$$ direction. Its amplitude is uniform over the $$yz$$ plane.As the wave moves, does its frequency
  • increase
  • decrease
  • stay constant
  • none
Rank the following kinds of waves according to their wavelength ranges from those with the largest typical or average wavelength to the smallest, noting any cases of equality: Rank the kinds of waves according to their speeds in vacuum from fastest to slowest.
  • gamma rays
  • microwaves
  • radio waves
  • visible light
  • x-rays
Rank the following kinds of waves according to their wavelength ranges from those with the largest typical or average wavelength to the smallest, noting any cases of equality: Rank the kinds of waves according to their frequencies from highest to lowest.
  • gamma rays
  • microwaves
  • radio waves
  • visible light
  • x-rays
The ratio of contributions made by the electric field and magnetic field components to the intensity of an electromagnetic wave is :
(c = speed of electromagnetic waves)
  • $$1:1$$
  • $$1:c$$
  • $$1:c^2$$
  • $$c:1$$
The displacement current will be
  • $$6.9\mu A$$
  • $$9.6\mu A$$
  • $$6.3\mu A$$
  • $$5.7\mu A$$
A collimated beam of light of flux density $$3k Wm^{-2}$$ is incident normally on a $$100 mm^2$$ completely absorbing screen. If P is the pressure exerted on the screen and $$\Delta p$$ is the momentum transferred to the screen during a 1000 s interval, then
  • $$P=10^{-3} N m^{-2}$$
  • $$P=10^{-4} N m^{-2}$$
  • $$\Delta p=10^{-4} kg ms^{-1}$$
  • $$\Delta p=10^{-5} kg ms^{-1}$$
A small metallic ball is suspended in a uniform electric field by a thread. If high energy X-rays are made to fall on it , then:
  • ball will be displaced in opposite direction to the direction of field
  • ball will be displaced in the direction of field
  • ball will remain in equilibrium state
  • ball will start oscillating
The incident intensity on a horizontal surface at sea level from the sun is about $$1 kW m^{-2}$$. Assuming that 50 per cent of this intensity is reflected and 50 per cent is absorbed, determine the radiation pressure on this horizontal surface (in pascals).
  • $$8.2\times 10^{-2}$$
  • $$5\times 10^{-6}$$
  • $$3\times 10^{-5}$$
  • $$6\times 10^{-5}$$
A parallel beam of light is incident normally on a plane surface absorbing 40 % of the light and reflecting the rest. If the incident beam carries 60 watt of power, the force exerted by it on the surface is:
  • $$3.2 \times 10^{-8}\, N$$
  • $$3.2 \times 10^{-7}\, N$$
  • $$5.2 \times 10^{-7}\, N$$
  • $$5.12 \times 10^{-8}\, N$$
Light of intensity$$ = 3 W/m^{2}$$ is incident on a perfectly absorbing metal surface of area  $$1 m^{2}$$ making an angle of $$60^0$$ with the normal. If the force exerted by the photons on the surface is $$p \times 10^{-9}$$ (in Newton), then the value of p is :
  • 5
  • 2
  • 1
  • 3
A pulse of light of duration $$100\ ns$$ is absorbed completely by a small object initially at rest. Power of the pulse is $$30\ mW$$ and the speed of light $$3\times 10^8 m/s.$$ The final momentum of the object is
  • $$0.3\times 10^{-17} kg\ ms^{-1}$$
  • $$1.0\times 10^{-17} kg\ ms^{-1}$$
  • $$3\times 10^{-17} kg\ ms^{-1}$$
  • $$9.0\times 10^{-17} kg ms^{-1}$$
Sea water at frequency $$\nu \  =\  4\  x\  { 10 }^{ 8 }$$ Hz has permittivity $$\varepsilon  \  \approx \  80\  { \varepsilon   }_{ 0 }$$, permeability $$\mu \  \approx \  { \mu  }_{ 0 }$$ and resistivity $$\rho \  =\  0.25\  \Omega m$$. Imagine a parallel plate capacitor immersed in sea water and driven by an alternating voltage source V(t) = $${ V }_{ 0 }\  \sin { \  (2\pi \nu t) }$$. The of amplitude of the displacement current density to the conduction current density is
  • $$\dfrac { 2 }{ 3 }$$
  • $$\dfrac { 4 }{ 9 }$$
  • $$\dfrac { 9 }{ 4 }$$
  • 2
Which of the following electromagnetic waves is used in medicine to destroy cancer cell?
  • IR- rays
  • Visible rays
  • Gamma rays
  • Ultraviolet rays
Choose the correct answer from the alternatives given.
Assume a bulb of efficiency 2.5% as a point source. The peak values of electric and magnetic fields produced by the radiation coming from a 100 W bulb at a distance of 3 m is respectively 
  • $$2.5 \, V \, m^1, \, 3.6 \, \times \, 10^{-8} T$$
  • $$4.2 \, V \, m^1, \, 2.8 \, \times \, 10^{-8} T$$
  • $$4.08 \, V \, m^1, \, 1.36 \, \times \, 10^{-8} T$$
  • $$3.6 \, V \, m^1, \, 3.6 \, \times \, 10^{-8} T$$
Choose the correct answer from the alternatives given.
A parallel plate capacitor with plate area $$A$$ and separation between the plates $$d$$ is charged by a constant current $$I$$. Consider a plane surface of area $$\dfrac{A}{2}$$ parallel to the plate and drawn between the plates. The displacement current through the area is :
  • I
  • $$\dfrac{I}{2}$$
  • $$\dfrac{I}{4}$$
  • $$\dfrac{I}{8}$$
A $$1.5\ kW$$ (kilo-watt) laser beam of wavelength $$6400 \mathring A$$ is used to levitate a thin aluminium disc of same area as the cross section of the beam. The laser light is reflected by the aluminium disk without any absorption. The mass of the disc is close to:
  • $$10^{-9}\ kg$$
  • $$10^{-3}\ kg$$
  • $$10^{-4}\ kg$$
  • $$10^{-6}\ kg$$
If $$v_{g}, v_{x}$$, and $$v_{m}$$ are speeds of gamma rays, $$X$$ rays, and microwaves respectively in vacuum, then:
  • $$V_{g} < V_{x} < V_{m}$$
  • $$V_{g}>V_{x}>V_{m}$$
  • $$V_{g} < V_{x}> V_{m}$$
  • $$V_{g}=V_{x}=V_{m}$$
A plane electromagnetic wave travels in free space along X-direction. If the value of $$\overrightarrow { B } $$ (in tesla) at a particular point in space and time is $$1.2 \times {10}^{-8} \hat {k}$$, the value of $$\overrightarrow { E } $$ (in V $${m}^{-1}$$) at that point is,
  • $$1.2\ \hat {j}$$
  • $$3.6\ \hat {k}$$
  • $$1.2\ \hat {k}$$
  • $$3.6\ \hat {j}$$
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