CBSE Questions for Class 12 Medical Physics Dual Nature Of Radiation And Matter Quiz 7 - MCQExams.com

The minimum intensity of light to be detected by human eye is $${ 10 }^{ -10 }W/{ m }^{ 2 }$$. The number of photons of wavelength $$5.6\times { 10 }^{ -7 }m$$ entering the eye, with pupil area $${ 10 }^{ -6 }{ m }^{ 2 }$$, per second for vision will be nearly
  • $$100$$
  • $$200$$
  • $$300$$
  • $$400$$
If alpha particle, proton and electron move with the same momentum, then their respective de-Broglie wavelengths $${ \lambda  }_{ \alpha  },{ \lambda  }_{ p },{ \lambda  }_{ e }$$ are related as
  • $${ \lambda }_{ \alpha }={ \lambda }_{ p }={ \lambda }_{ e }$$
  • $${ \lambda }_{ \alpha }<{ \lambda }_{ p }<{ \lambda }_{ e }$$
  • $${ \lambda }_{ \alpha }>{ \lambda }_{ p }>{ \lambda }_{ e }$$
  • $${ \lambda }_{ p }>{ \lambda }_{ e }>{ \lambda }_{ \alpha }$$
  • $${ \lambda }_{ p }<{ \lambda }_{ e }<{ \lambda }_{ \alpha }$$
De-Broglie wavelength of a body of mass $$1$$kg moving with velocity of $$2000 \>$$m$$/$$s is?
  • $$3.32\times 10^{-27}\overset{o}{A}$$
  • $$1.5\times 10^7\overset{o}{A}$$
  • $$0.55\times 10^{-22}\overset{o}{A}$$
  • None of these
In a photoemissive cell with exciting wave length $$\lambda$$, the fastest electron has a speed $$v$$. If the exciting wavelength is change to $$3\lambda / 4$$, then the speed of the fastest emitted electron will be
  • $$v\left (\dfrac {3}{4}\right )^{\dfrac {1}{2}}$$
  • $$v\left (\dfrac {4}{3}\right )^{\dfrac {1}{2}}$$
  • Less than $$v\left (\dfrac {4}{3}\right )^{\dfrac {1}{2}}$$
  • Greater than $$v\left (\dfrac {4}{3}\right )^{\dfrac {1}{2}}$$
The de-Broglie wavelength of a neutron at $${ 27 }^{ o }C$$ is $$\lambda $$. What will be its wavelength at $${ 927 }^{ o }C$$?
  • $$\lambda /2$$
  • $$\lambda /3$$
  • $$\lambda /4$$
  • $$\lambda /9$$
Threshold wavelength of a metal is $$4000\overset{o}{A}$$. If light of wavelength $$3000\overset{o}{A}$$ irradiates the surface, the maximum kinetic energy of photoelectron is?
  • $$1.7$$eV
  • $$1.6$$eV
  • $$1.5$$eV
  • $$1.0$$eV
The de-Broglie wavelength of an electron and the wavelength of a photon are the same. The ratio between the energy of that photon and the momentum of that electron is (c =velocity of light, h= Planck's constant)
  • $$h$$
  • $$c$$
  • $$\dfrac {1}{c}$$
  • None of these
The speed of an electron having a wavelength of $${ 10 }^{ -10 }m$$ is
  • $$4.24\times { 10 }^{ 6 }m/s\quad $$
  • $$5.25\times { 10 }^{ 6 }m/s$$
  • $$6.26\times { 10 }^{ 6 }m/s\quad $$
  • $$7.25\times { 10 }^{ 6 }m/s\quad $$
If alpha particle and deutron move with velocity $$v$$ and $$2v$$ respectively, the ratio of their de-Broglie wavelength will be _____
  • $$2 : 1$$
  • $$1 : \sqrt {2}$$
  • $$1 : 1$$
  • $$\sqrt {2} : 1$$

The energies of the incident photons are $$3,4,5\,eV.$$ The work functions of the metals are $$0.5,1.5,2.5\,eV.$$ The maximum K.E.s of the photoelectrons are in the ratio:
  • $$3:4:5$$
  • $$1:3:5$$
  • $$1:1:1$$
  • $$5:3:1$$
If the kinetic energy of free electron is made double; the new de-Broglie wavelength will be __________ times that of initial wavelength.
  • $$\dfrac { 1 }{ \sqrt { 2 } } $$
  • $$\sqrt { 2 } $$
  • $$2$$
  • $$\dfrac { 1 }{ 2 } $$
Light of wavelength $$\lambda $$ falls on a metal having work function $$\cfrac { hc }{ { \lambda  }_{ 0 } } $$. Photoelectric effect will take place only if
  • $$\lambda \ge { \lambda }_{ 0 }$$
  • $$\lambda \ge 2{ \lambda }_{ 0 }$$
  • $$ \lambda \le { \lambda }_{ 0 }$$
  • $$\lambda =4{ \lambda }_{ 0 }$$
A body of mass $$100 g$$ moves at the speed of $$36 { km }/{ h }$$. The de-Broglie wavelength related to it is of the order _________ $$m$$.
$$\left( h=6.626\times { 10 }^{ -34 }Js \right) $$
  • $${ 10 }^{ -24 }$$
  • $${ 10 }^{ -14 }$$
  • $${ 10 }^{ -34 }$$
  • $${ 10 }^{ -44 }$$
If the linear momentum of a particle is $$2.2 \times 10^4\, kg\, ms^{-1}$$, then what will be its de-Broglie wavelength ? (Take hr. $$6.6 \times 10^{-34}\, Js$$) 
  • $$3 \times 10^{-29}\, m$$
  • $$3 \times 10^{-29}\, nm$$
  • $$6 \times 10^{-29}\, m$$
  • $$6 \times 10^{-29}\, nm$$
The wavelength $$\lambda$$ of a photon and the de-Broglie wavelength of an electron have the same value. Find the ratio of energy of photon of the kinetic energy of electron in terms of mass m, speed of light c and planck constant.
  • $$\displaystyle\frac{\lambda mc}{h}$$
  • $$\displaystyle\frac{hmc}{\lambda}$$
  • $$\displaystyle\frac{2hmc}{\lambda}$$
  • $$\displaystyle\frac{2\lambda mc}{h}$$
What is the photon flux and photon density at 2 m from the lamp?
  • $$5.9\times 10^{14} photons cm^{-2}, 2\times 10^4 photons cm^{-2}$$
  • $$2\times 10^4 photons cm^{-2}, 5.9\times 10^{14} photons cm^{-2}$$
  • $$5.9\times 10^{10} photons cm^{-2}, 2\times 10^3 photons cm^{-2}$$
  • $$2\times 10^3 photons cm^{-2}, 5.9\times 10^{10} photons cm^{-2}$$
An electron in an electron microscope with initial velocity $$v_0i$$ enters a region of a stray transverse electric field $$E_0j$$. The time taken for the change in its de Broglie wavelength from the initial value of $$\lambda$$ to $$\dfrac{\lambda}{3}$$ is proportional to.
  • $$E_0$$
  • $$\displaystyle\frac{1}{E_0}$$
  • $$\displaystyle\frac{1}{\sqrt{E_0}}$$
  • $$\displaystyle\sqrt{E_0}$$
The approximate number of photons in a femtosecond $$(10^{-15}s)$$ pulse of 600 nanometers wavelenghth light from a 10-kilowatt peak-power dye laser is
  • $$10^3$$
  • $$10^7$$
  • $$10^{11}$$
  • $$10^{15}$$
  • $$10^{18}$$
An electron and a photon have same wavelength of $$10^{-9}$$m. If E is the energy of the photon and p is the momentum of the electron, the magnitude of E/p in SI units is?
  • $$1.00\times 10^{-9}$$
  • $$1.50\times 10^8$$
  • $$3.00\times 10^8$$
  • $$1.20\times 10^7$$
The energy of a $$K$$-electron in tungsten is $$-20keV$$ and of an $$L$$-electrons is $$-2keV$$. The wavelength of X-rays emitted when there is electron jump from $$L$$ to $$K$$ shell:
  • $$0.3443\mathring { A } $$
  • $$0.6887\mathring { A } $$
  • $$1.3982\mathring { A } $$
  • $$2.78\mathring { A } $$
The formula of kinetic mass of photon is? Where h is Planck's constant, v is frequency of the photon and c is its speed.
  • $$\displaystyle\frac{hv}{c}$$
  • $$\displaystyle\frac{hv}{c^2}$$
  • $$\displaystyle\frac{hc}{v}$$
  • $$\displaystyle\frac{c^2}{hv}$$
A particle is projected horizontally with a velocity $$10\ m/s$$. What will be the ratio of de-Broglie wavelengths of the particle, when the velocity vector makes an angle $$30^{\circ}$$ and $$60^{\circ}$$ with the horizontal?
  • $$\sqrt {3} : 1$$
  • $$1 : \sqrt {3}$$
  • $$2 : \sqrt {3}$$
  • $$\sqrt {3} : 2$$
de-Broglie wavelength of atom at $$TK$$ absolute temperature will be
  • $$\cfrac { h }{ mKT } $$
  • $$\cfrac { h }{ \sqrt { 3mKT } } $$
  • $$\cfrac { \sqrt { 2mKT } }{ h } $$
  • $$\sqrt { 2mKT } $$
The momentum associated with photon is given by __________.
  • $$h \upsilon$$
  • $$\displaystyle \frac{h \upsilon}{c}$$
  • $$h E$$
  • $$h \lambda$$
An electron of mass m with an initial velocity $$\overrightarrow{V}=V_0\hat{i}(V_0 > 0)$$ enters an electric field $$\overrightarrow{E}=-E_0\hat{i}$$($$E_0=$$constant $$> 0$$) at $$t=0$$. If $$\lambda_0$$ is its de-Broglie wavelength initially, then its de-Broglie wavelength at time t is?
  • $$\lambda_0\left(\displaystyle 1+\frac{eE_0}{mV_0}t\right)$$
  • $$\lambda_0 t$$
  • $$\displaystyle\frac{\lambda_0}{\left(\displaystyle 1+\frac{eE_0}{mV_0}t\right)}$$
  • $$\lambda_0$$
A charged particle is accelerated from rest through a certain potential difference. The de Broglie wavelength is $${ \lambda  }_{ 1 }$$ when it is accelerated through $${V}_{1}$$ and is $${ \lambda  }_{ 2 }$$ when accelerated through $${V}_{2}$$. The ratio $${ \lambda  }_{ 1 }/{ \lambda  }_{ 2 }$$ is
  • $${ V }_{ 1 }^{ 3/2 }:{ V }_{ 2 }^{ 3/2 }$$
  • $${ V }_{ 2 }^{ 1/2 }:{ V }_{ 1 }^{ 1/2 }$$
  • $${ V }_{ 1 }^{ \cfrac { 1 }{ 2 } }:{ V }_{ 2 }^{ \cfrac { 1 }{ 2 } }$$
  • $${ V }_{ 1 }^{ 2 }:{ V }_{ 2 }$$
An electron of mass m and a photon have same energy E.Find out the ratio of de-Brogile wavelength associated with them is (c- velocity of light)
  • $$c { \left[ 2mE \right] }^{ \dfrac { 1 }{ 2 } }$$
  • $$\dfrac { 1 }{ c } { \left[ \dfrac { 2m }{ E } \right] }^{ \dfrac { 1 }{ 2 } }$$
  • $$\dfrac { 1 }{ c } { \left[ \dfrac { E }{ 2m } \right] }^{ \dfrac { 1 }{ 2 } }$$
  • $${ \left[ \dfrac { E }{ 2m } \right] }^{ \dfrac { 1 }{ 2 } }$$
A material particle with a rest mass $$m_0$$ is moving with a velocity of light c. Then determine the wavelength of the de Broglie wave associated with it is.
  • $$\displaystyle(h/m_0c)$$
  • zero
  • $$\displaystyle\infty $$
  • $$\displaystyle(m_0c/h)$$
The frequencies of X-rays, $$\gamma$$ rays and Ultra violet rays are respectively incident on a metal, having work function is $$0.5eV$$. The ratio of maximum speed of emtted electrons is
  • $$p< q, q> r$$
  • $$p> q, q >r$$
  • $$p< q, q< r$$
  • $$p> q, q< r$$
About 5% of the power of a 100W light bulb is converted to visible radiation.What is the average intensity of visible radiation at distance of 10 m.
  • 0.4 W / $$m^2$$
  • 0.04 W / $$m^2$$
  • 0.004 W / $$m^2$$
  • 0.0004 W / $$m^2$$
Choose the correct answer from the alternatives given.
The photon energy in units of $$eV$$ for electromagnetic waves of wavelength $$2\ cm$$ is then
  • $$2.5 \, \times \, 10^{-19}$$
  • $$5.2 \, \times \, 10^{16}$$
  • $$3.2 \, \times \, 10^{-16}$$
  • $$6.2 \, \times \, 10^{-5}$$
A $$100 W$$ sodium lamp radiates energy uniformly in all directions. The lamp is located at the centre of a large sphere that absorbs all the sodium light which is incident on it. The  wavelength of the sodium light is $$589 nm$$. The number of photons delivered per second to the sphere is
  • $$3 \, \times \, 10^{15}$$
  • $$3 \, \times \, 10^{10}$$
  • $$3 \, \times \, 10^{20}$$
  • $$3 \, \times \, 10^{19}$$
A blue lamp mainly emits light of wavelength 4500 $$\mathring{A}$$. The lamp is rated at 150 W and 8% of the energy is emitted as visible light. The number of photons emitted by the lamp per second is:
  • $$3 \, \times \, 10^{19}$$
  • $$3 \, \times \, 10^{24}$$
  • $$3 \, \times \, 10^{20}$$
  • $$3 \, \times \, 10^{18}$$
Which of the following functions is performed by a photo-electric cell?
  • It converts electrical energy into light
  • It converts light energy into electrical energy
  • It conserves sound energy
  • It converts electrical energy into sound
If h is Plancks constant, the momentum of a photon of wavelength 0.01 $$A^o$$ is
  • $$10^{-2}h$$
  • h
  • $$10^2$$
  • $$10^{12}h$$
A laser beam is for locating distant objects because
  • it is monochromatic
  • it is constant
  • it is not observed
  • it has small angular spread
The maximum value of photoelectric current is called:
  • base current
  • Saturation current
  • collector current
  • emitter current
The energy flux of sunlight reaching the surface of the earth is $$1.388 \, \times \, 10^3 Wm^{-2}$$. The photons in the sunlight have an average wavelength of 550 nm. How many photons per square metre are incident on the earth per second?
  • $$4 \, \times \, 10^{21}$$
  • $$4 \, \times \, 10^{34}$$
  • $$4 \, \times \, 10^{31}$$
  • $$4 \, \times \, 10^{28}$$
The wavelength of light in the visible region is about $$390 nm$$ for violet colour and about $$760 nm$$ for red colour. The energy of photon in $$eV$$ at violet end is
  • $$2.32$$
  • $$3.19$$
  • $$1.42$$
  • $$4.13$$
The linear momentum of a 3 MeV photon is:
  • 0.01 $$eV \, sm^{-1}$$
  • 0.02 $$eV \, sm^{-1}$$
  • 0.03 $$eV \, sm^{-1}$$
  • 0.04 $$eV \, sm^{-1}$$
A proton, a neutron, an electron and an $$\alpha$$-particle have same energy. Then their de Broglie wavelengths compare as :
  • $$\lambda_p\, = \,\lambda_n\, > \,\lambda_e \,> \,\lambda_\alpha$$
  • $$\lambda_\alpha\, < \,\lambda_p\, = \,\lambda_n \,< \,\lambda_e $$
  • $$\lambda_e\, < \,\lambda_p\, = \,\lambda_n \,> \,\lambda_\alpha$$
  • $$\lambda_e\, = \,\lambda_p\, = \,\lambda_n \, = \,\lambda_\alpha$$
When the velocity of an electron increases, its de Broglie wavelength:
  • increases
  • decreases
  • remains same
  • may increase or decrease
The de Broglie wavelength of an electron in a metal at $$27^{\circ}C$$ is $$(Given \, m_e \, = \, 9.1 \, \times \, 10^{-31} \, kg,\,  k_B \, = \, 1.38 \, \times \, 10^{-23} \, J \, K^{-1})$$ 
  • $$6.2 \, \times \, 10^{-9} \, m$$
  • $$6.2 \, \times \, 10^{-10} \, m$$
  • $$6.2 \, \times \, 10^{-8} \, m$$
  • $$6.2 \, \times \, 10^{-7} \, m$$
A monochromatic light of frequency $$3 \, \times \, 10^{14} \, Hz$$ is produced by a LASER, emits the power of $$3 \, \times \, 10^{-3}\, W$$. Find how many numbers of photons are emitted per second.
  • $$1.5 \, \times \, 10^{16}$$
  • $$2.5 \, \times \, 10^{16}$$
  • $$4.5 \, \times \, 10^{16}$$
  • $$8.5 \, \times \, 10^{16}$$
A particle of mass $$4m$$ at rest decays into two particles of masses $$m$$ and $$3m$$ having non-zero velocities. The ratio of the de Broglie wavelengths of the particles 1 and 2 is:
  • $$\dfrac{1}{2}$$
  • $$\dfrac{1}{4}$$
  • $$2$$
  • $$1$$
There are two sources of light, each emitting with a power of 100 W. One emits X-rays of wavelength 1 nm and the other visible light of 500 nm. The ratio of number of photons of X-rays to the photons of visible light of the given wavelength is:
  • 1:500
  • 1:400
  • 1:300
  • 1:200
Relativistic corrections become necessary when the expression for the kinetic energy $$\dfrac{1}{2} mv^2$$, becomes comparable with $$mc^2$$, where m is the mass of the particle. At what de Broglie waxelength will relativistic corrections become important for an electron?
  • $$\lambda \, = \, l \, nm$$
  • $$\lambda \, = \, l0 \, nm$$
  • $$\lambda \, = \, l0^{-1} \, nm$$
  • $$\lambda \, = \, l0^{-4} \, nm$$
Consider the four gases hydrogen, oxygen, nitrogen and helium at the same temperature. Arrange them in the increasing order of the de Broglie wavelengths of their molecules.
  • Hydrogen, helium, nitrogen, oxygen
  • Oxygen, nitrogen, hydrogen, helium
  • Oxygen, nitrogen, helium, hydrogen
  • Nitrogen, oxygen, helium, hydrogen
Two particles $$A_1$$ and $$A_2$$ of masses $$m_1, \, m_2 \, (m_1 \, > \, m_2)$$ have the same de Broglie wavelength. Then
  • their momenta are the same.
  • their energies are the same.
  • momentum of $$A_1$$ is less than momentum of $$A_2$$
  • energy of $$A_1$$ is more than the energy of $$A_2$$
A particle $$A$$ of mass $$m$$ and initial velocity $$v$$ collides with a particle $$B$$ of mass $$\cfrac{m}{2}$$ which is at rest. The collision is head on, and elastic. The ratio of the de-Broglie wavelengths $${ \lambda  }_{ A }$$ and $${ \lambda  }_{ B }$$ after the collision is :
  • $$\cfrac { { \lambda }_{ A } }{ { \lambda }_{ B } } =\cfrac { 1 }{ 2 } $$
  • $$\cfrac { { \lambda }_{ A } }{ { \lambda }_{ B } } =\cfrac { 1 }{ 3 } $$
  • $$\cfrac { { \lambda }_{ A } }{ { \lambda }_{ B } } =2$$
  • $$\cfrac { { \lambda }_{ A } }{ { \lambda }_{ B } } =\cfrac { 2 }{ 3 } $$
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