Photoelectric Effect & Einstein's Equation — Practice Questions

Free NEET Physics multiple-choice questions on Photoelectric Effect & Einstein's Equation. Attempt each question and reveal the answer with a full explanation.

In the photoelectric effect, if the intensity of incident light is doubled, then: The saturation photocurrent is doubled. The maximum kinetic energy is doubled. The stopping potential is doubled. The threshold frequency is halved. The phenomenon of photoelectric effect was explained by Einstein by assuming that: Light is made of discrete packets of energy called photons Light is an electromagnetic wave Electrons behave like waves Matter is composed of atoms The threshold wavelength for a photoelectric emission from a material is 5200 Å. Photoelectrons will be emitted when this material is illuminated with monochromatic radiation from a: 50 W ultraviolet lamp 1 W infrared lamp 50 W infrared lamp 10 W sodium lamp The momentum of a photon of energy 1 MeV in kg m/s will be: 5 10 -22 0.33 10 -22 7 10 -24 10 -22 A photo-cell is illuminated by a source of light which is placed at a distance d from the cell. If the distance becomes d/2 , then the number of electrons emitted per second will be: Four times Two times One-fourth Same Monochromatic light of frequency 6.0 10 14 Hz is produced by a laser. The power emitted is 2.0 10 -3 W . How many photons per second on average are emitted by the source? 5 10 15 5 10 16 5 10 17 5 10 14 Light of frequency 1.5 times the threshold frequency is incident on a photosensitive material. What will be the photoelectric current if the frequency is halved and intensity is doubled? Zero Doubled Four times Halved A 5W source emits monochromatic light of wavelength 5000 . When placed 0.5 m away, it liberates photoelectrons from a photosensitive metallic surface. When the source is moved to a distance of 1 m , the number of photoelectrons liberated will be reduced by a factor of: 4 2 8 16 The work function of a surface is . If a photon of energy E falls on it, the maximum kinetic energy of the emitted photoelectron is K . If the energy of the incident photon is increased to 2E , the new maximum kinetic energy of the photoelectron will be: K + E 2K 2K + K + 2 The threshold frequency for a metallic surface corresponds to an energy of 6.2 eV and the stopping potential for a radiation incident on this surface is 5 V . The incident radiation lies in the: Ultra-violet region Infra-red region Visible region X-ray region In a photoelectric experiment, the stopping potential V 0 is plotted against the reciprocal of the wavelength 1/ . The slope of this graph is: hc/e h/e hc c/e A metal surface of work function 1.07 eV is irradiated with light of wavelength 332 nm . The retarding potential required to stop the fastest photoelectrons is: 2.66 V 1.07 V 3.73 V 4.80 V Light of frequency 1.5 times the threshold frequency is incident on a photosensitive material. If the frequency is halved and intensity is doubled, the photoelectric current becomes: Zero Doubled Four times Halved If the threshold wavelength for a metal is 600 nm , what is the maximum kinetic energy of photoelectrons emitted when light of wavelength 400 nm is incident? 1.03 eV 0.52 eV 3.10 eV 2.07 eV The threshold frequency for a certain metal is 0 . When light of frequency 2 0 is incident on it, the maximum velocity of photoelectrons is 4 10 6 m/s . If the frequency of incident radiation is increased to 5 0 , then the maximum velocity of photoelectrons will be: 8 10 6 m/s 2 10 6 m/s 16 10 6 m/s 4 10 7 m/s A beam of light of wavelength 600 nm from a distant source falls on a photosensitive surface at a rate of 2 mW . The number of photons striking the surface per second is: 6 10 15 3 10 16 9 10 18 1 10 12 The variation of photoelectric current with the collector plate potential for two different intensities I 1 and I 2 ( I 2 > I 1 ) of incident radiation of the same frequency is correctly shown by: Curves with same stopping potential but different saturation currents Curves with different stopping potentials but same saturation current Parallel straight lines Curves with different stopping potentials and different saturation currents Photons of energy 6 eV are incident on a metal surface whose work function is 4 eV . The minimum kinetic energy of the emitted photoelectrons is: 0 eV 2 eV 10 eV 1 eV A 20 W laser source emits monochromatic light of wavelength 663 nm . The number of photons emitted per second is: ( h = 6.63 10 -34 J s ) 6.67 10 19 3.33 10 19 6.67 10 20 2.0 10 20 When light of frequency is incident on a metal surface, the stopping potential is V 0 . When light of frequency 2 is incident on the same surface, the stopping potential is V' 0 . The relation between them is: V' 0 > 2V 0 V' 0 = 2V 0 V' 0 < 2V 0 V' 0 = V 0 The threshold frequency of a metal is 10 15 Hz . When light of frequency 4 10 15 Hz is incident on the metal, the maximum kinetic energy of the emitted photoelectrons is: ( h = 6.63 10 -34 J s ) 1.989 10 -18 J 1.989 10 -19 J 6.63 10 -19 J 4.42 10 -18 J A radio transmitter operates at a frequency of 1000 kHz and a power of 66.3 kW . The number of photons emitted per second is: 10 32 10 30 10 35 10 28 Two monochromatic beams of light A and B have the same intensity. Beam A has a higher frequency than beam B. Which of the following is true? Beam B has more photons per second per unit area than A. Beam A has more photons per second per unit area than B. Both beams have the same number of photons per second per unit area. None of these. Light of frequency is incident on a surface of work function W 0 . The maximum kinetic energy of photoelectrons is K . If the intensity of light is tripled, the maximum kinetic energy becomes: K 3K K/3 9K Light of two different frequencies whose photons have energies 1 eV and 2.5 eV respectively, illuminate a metallic surface whose work function is 0.5 eV successively. The ratio of maximum speeds of emitted electrons will be: 1 : 2 1 : 4 1 : 1 1 : 5 What is the force exerted by a 10 W laser beam on a non-reflecting surface when it is incident normally? 3.33 10 -8 N 6.67 10 -8 N 3.33 10 -7 N 0 N When the wavelength of light incident on a photoelectric cell is reduced from 1 to 2 , the change in stopping potential is: (hc/e) [( 1 - 2) / ( 1 2)] (hc/e) [( 1 + 2) / ( 1 2)] (hc/e) [ 1 2 / ( 1 - 2)] Zero Which of the following graphs correctly shows the variation of 1/ with V for an electron accelerated through potential V ? A straight line passing through the origin A parabola A rectangular hyperbola A straight line with a non-zero intercept Light of frequency 1.9 times the threshold frequency is incident on a photosensitive surface. If the frequency is doubled and the intensity is halved, the photoelectric current will: Be halved Be doubled Remain unchanged Become zero In a photoelectric experiment, the stopping potential V 0 is plotted against the frequency . The intercept on the V 0 -axis is: - /e /h -h/e /e If the wavelength of incident light on a metal surface is decreased from 600 nm to 400 nm , the change in stopping potential will be: 1.03 V 0.52 V 2.06 V 1.55 V A photoelectric surface is illuminated successively by monochromatic light of wavelength and /2 . If the maximum kinetic energy of the emitted photoelectrons in the second case is 3 times that in the first case, the work function of the surface of the material is: ( h = Planck's constant, c = speed of light) hc 2 hc hc 3 3hc A laser beam of power P and wavelength is incident normally on a perfectly reflecting surface. The force exerted by the beam on the surface is: 2P c P c 2P hc P 2c The slope of the graph plotted between the square of maximum velocity ( v max 2 ) of photoelectrons and the frequency ( ) of incident radiation is: 2h/m h/m h/e e/m The photoelectric effect can be observed when: Incident frequency > Threshold frequency Incident wavelength > Threshold wavelength Incident energy < Work function Intensity is high regardless of frequency The number of photons per second entering the eye from a point source of light of power 10 -10 W and wavelength 500 nm is approximately: 2.5 10 8 2.5 10 10 5 10 7 1.2 10 11 When the frequency of incident radiation on a metallic surface is doubled, the maximum kinetic energy of the photoelectrons: Becomes more than double Becomes exactly double Becomes less than double Remains unchanged A gamma-ray photon has a wavelength of 10 -12 m . Its energy is approximately: 1.24 MeV 12.4 MeV 0.124 MeV 124 keV If the wavelength of light incident on a metal is halved, the maximum kinetic energy of the photoelectrons will be: More than double Exactly double Exactly half Less than double A photon of wavelength and an electron have the same momentum. The energy of the photon is E ph and the kinetic energy of the electron is E e . Which of the following is correct? E ph > E e E ph < E e E ph = E e E ph = 2E e If the wavelength of light incident on a photoelectric cell is 3000 r , what is the maximum kinetic energy of photoelectrons if the work function of the metal is 2.0 eV ? (Use hc = 12400 eV r ) 2.13 eV 4.13 eV 1.13 eV 3.13 eV If the threshold frequency for a metal is 1.2 10 15 Hz , what is the work function of the metal? ( h = 6.63 10 -34 J s ) 4.97 eV 3.12 eV 6.21 eV 2.45 eV The number of photons emitted per second by a 60 W source of monochromatic light of wavelength 663 nm is: ( h = 6.63 10 -34 J s ) 2 10 20 2 10 18 3 10 20 1.5 10 20 Light of wavelength falls on a metal surface. The maximum kinetic energy of emitted electrons is K . If the wavelength is changed to /2 , the new maximum kinetic energy K' will be: K' > 2K K' = 2K K' < 2K K' = K/2 Which of the following statements is FALSE regarding photons? The speed of a photon is different in different inertial frames. Photons are not deflected by electric and magnetic fields. Photons have zero rest mass. In a photon-particle collision, the total energy and total momentum are conserved. The intensity of radiation from a point source is I . If the distance from the source is doubled, the number of photoelectrons emitted per second from a surface will: Decrease to 1/4 Decrease to 1/2 Increase by 4 Remain unchanged A metal surface of work function W is irradiated with light of frequency . If the frequency is doubled, the maximum kinetic energy of the photoelectrons will be: 2h - W 2(h - W) h - 2W h + W Which of the following represents the correct variation of the stopping potential ( V 0 ) with the frequency ( ) of the incident radiation for two different metals having work functions 1 and 2 where 1 > 2 ? Parallel lines where the line for 1 is shifted to the right (higher threshold frequency). Lines with different slopes intersecting at the y-axis. Parallel lines where the line for 1 is shifted to the left. Non-parallel lines meeting at the origin. A radiation of intensity I is incident on a surface. If 50 % of the radiation is reflected and the rest is absorbed, the radiation pressure exerted on the surface for normal incidence is ( c is the speed of light): 1.5 I/c 2 I/c I/c 0.5 I/c If the wavelength of light incident on a photoelectric cell is reduced from 400 nm to 360 nm , the change in stopping potential will be approximately: 0.34 V 0.15 V 0.68 V 1.2 V For an electron accelerated through a potential V , the plot of vs V is a straight line. The slope of this line is: -1/2 1/2 -1 1 When monochromatic light of wavelength is incident on a metal, the stopping potential is 3V 0 . When wavelength 2 is incident, the stopping potential is V 0 . The threshold wavelength is: 4 3 1.5 8 Which of the following figures correctly shows the variation of collector current ( I ) with collector plate potential ( V ) for a photosensitive surface when light of two different frequencies 1 and 2 (with 1 > 2 ) but same intensity is incident? Two curves starting from different negative potentials on V-axis but ending at the same saturation current level Two curves starting from the same negative potential but ending at different saturation current levels Two curves starting from different negative potentials and ending at different saturation current levels Two parallel straight lines If the wavelength of light incident on a metal is halved, then the maximum kinetic energy of the emitted photoelectrons: Becomes more than double Becomes double Becomes half Becomes less than double The threshold frequency of a metal is f 0 . When light of frequency 2f 0 is incident on it, the maximum velocity of electrons is v 1 . When the frequency of incident radiation is 5f 0 , the maximum velocity of electrons is v 2 . The ratio v 1/v 2 is: 1/2 1/4 1/ 2 2 The work function of a metal is W 0 . If light of frequency is incident on it, the maximum kinetic energy of photoelectrons is K . If the frequency is tripled, the maximum kinetic energy will be: 3K + 2W 0 3K 3K - 2W 0 K + 2h In a photoelectric experiment, the graph of stopping potential V 0 versus the frequency of incident light is plotted for two metals A and B. If the two lines are parallel, which physical quantity is the same for both metals? Planck's constant Work function Threshold frequency Saturation current Light of frequency 1.5 0 is incident on a photosensitive surface. If the frequency is doubled and intensity is halved, the photoelectric current will: Be halved Remain same Become zero Be doubled An electron of mass m and a photon have the same de-Broglie wavelength . If the energy of the photon is E ph and the kinetic energy of the electron is K e , then the ratio E ph /K e is: 2mc / h h / 2mc 2h / mc mc / 2h The threshold frequency for a certain metal is 0 . When light of frequency = 2 0 is incident on it, the maximum velocity of photoelectrons is v . If the frequency of incident radiation is increased to 5 0 , the maximum velocity of photoelectrons will be: 2v v/2 4v 2 v The stopping potential V 0 as a function of the frequency of incident radiation is plotted for two different photoelectric surfaces A and B . The graphs are parallel straight lines. This implies that: Surface A and B have different work functions but the same h/e ratio Surface A and B have the same work function Surface A and B have the same threshold frequency The slope of the lines depends on the intensity of light The number of photons emitted per second by a source of power P and wavelength is N . If the wavelength is doubled and the power is halved, the number of photons emitted per second becomes: N 2N N/2 N/4 For a photoelectric surface, the threshold wavelength is L . When light of wavelength L/2 is incident, the maximum velocity of emitted photoelectrons is V . If the incident wavelength is changed to L/3 , the maximum velocity will be: 2 V 2V V/ 2 3 V The slope of the graph between the stopping potential ( V 0 ) and the reciprocal of wavelength ( 1/ ) in a photoelectric experiment is: hc/e h/e e/hc W 0/e When light of frequency 2 u 0 is incident on a metal plate, the maximum velocity of emitted photoelectrons is v 1 . If the frequency is increased to 10 u 0 , the maximum velocity becomes v 2 . The ratio v 2/v 1 is: 3 9 √3 √10 A photon of frequency is incident on a metal of threshold frequency 0 . If = 2 u 0 , the maximum kinetic energy of emitted photoelectrons is K . If the frequency is doubled, the new maximum kinetic energy will be: 3K 2K 4K K/2 The threshold wavelength for a metal is 3000 Å . If light of wavelength 2000 Å is incident, the maximum kinetic energy of the photoelectrons is approximately: ( hc = 12400 eVÅ ) 2.07 eV 4.14 eV 6.21 eV 1.03 eV According to the wave theory of light, the time required to eject a photoelectron from a metal surface is predicted to be: Quite large (hours) Instantaneous ( 10 -9 s ) Zero Independent of intensity The number of photons emitted per second by a 1 MW transmitter operating at 10 6 Hz is: 1.5 10 33 1.5 10 30 6.6 10 27 6.6 10 36 If the energy of a photon is E = 10 keV , its momentum in kg m/s is approximately: 5.33 10 -24 3.33 10 -27 1.33 10 -22 2.66 10 -25 Two radiations of photon energies 1 eV and 2.5 eV successively illuminate a photosensitive metallic surface of work function 0.5 eV . The ratio of the maximum speeds of the emitted electrons is: 1:2 1:4 1:1 2:1 What is the force exerted by a 10 W light beam on a perfectly reflecting surface if it is incident normally? 6.67 10 -8 N 3.33 10 -8 N 1.33 10 -7 N 2.00 10 -8 N A photosensitive metallic surface has work function, h 0 . If photons of energy 2h 0 fall on this surface, the electrons come out with a maximum velocity of 4 10 6 m/s . When the photon energy is increased to 5h 0 , then maximum velocity of photo electrons will be 2 10 7 m/s 2 10 6 m/s 8 10 5 m/s 8 10 6 m/s The figure shows a plot of photo current versus anode potential for a photo sensitive surface for three different radiations. Which one of the following is a correct statement ? Curves (b) and (c) represent incident radiations same frequencies having same intensity. Curves (a) and (b) represent incident radiations of different frequencies and different intensities Curves (a) and (b) represent incident radiations of same frequencies but of different intensities Curves (b) and (c) represent incident radiations of different frequencies and different intensities When the energy of the incident radiation is increased by 20%, the kinetic energy of the photoelectrons emitted from a metal surface increased from 0.5 , eV to 0.8 , eV . The work function of the metal is :- 0.65 , eV 1.0 , eV 1.3 , eV 1.5 , eV When a metallic surface is illuminated with radiation of wavelength , the stopping potential is V . If the same surface is illuminated with radiation of wavelength 2 , the stopping potential is V 4 . The threshold wavelength for the metallic surface is :- 4 5 5 2 3 In an experiment of photoelectric effect the stopping potential was measured to be V 1 and V 2 with incident light of wavelength and /2 , respectively. The relation between V 1 and V 2 is V 2 > 2V 1 V 2 < V 1 V 1 < V 2 < 2V 1 V 2 = 2V 1 When the light of frequency 2 0 (where 0 is threshold frequency), is incident on a metal plate, the maximum velocity of electrons emitted is v 1 . When the frequency of the incident radiation is increased to 5 0 , the maximum velocity of electrons emitted from the same plate is v 2 . The ratio of v 1 to v 2 is 4:1 1:4 1:2 2:1 If the stopping potential for photoelectrons emitted from a metal surface is zero, it means: The incident frequency is equal to the threshold frequency The incident frequency is zero The work function is zero The intensity is zero An electromagnetic wave of wavelength ' ' is incident on a photosensitive surface of negligible work function. If ' m ' mass is of photoelectron emitted from the surface has de-Broglie wavelength ' d ', then d= ( 2mc h ) 2 = ( 2mc h ) d 2 = ( 2h mc ) d 2 = ( 2m hc ) d 2 When two monochromatic lights of frequency, and 2 are incident on a photoelectric metal, their stopping potential becomes V s 2 and V s respectively. The threshold frequency for this metal is 3 2 3 3 2 2 If c is the velocity of light in free space, the correct statements about photon among the following are: A. The energy of a photon is E = h . B. The velocity of a photon is c . C. The momentum of a photon, p = h c . D. In a photon-electron collision, both total energy and total momentum are conserved. E. Photon possesses positive charge. Choose the correct answer from the options given below: A and B only A, B, C and D only A, C and D only A, B, D and E only For a metal of work function 6.6 eV , which of the following wavelengths of incident radiation does not give rise to the photoelectric effect? (Take Planck's constant as 6.6 10 -34 J s ) 200 nm 100 nm 50 nm 150 nm When light of frequency 2 0 (where 0 is threshold frequency) is incident on a metal plate, the maximum velocity of electrons emitted is v 1 . When the frequency of incident radiation is increased to 5 0 , the maximum velocity of electrons emitted from the same plate is v 2 . The ratio v 1/v 2 is: 1:2 1:4 4:1 2:1 A source S 1 is producing 10 15 photons per second of wavelength 5000 Å. Another source S 2 is producing 1.02 10 15 photons per second of wavelength 5100 Å. The ratio of power of S 2 to S 1 is: 1.00 1.02 2.01 0.98 Light of wavelength 500 nm is incident on a metal with work function 2.28 eV . The de-Broglie wavelength of the emitted electron is: 2.8 10 -9 m 2.8 10 -12 m < 2.8 10 -10 m < 2.8 10 -12 m The wavelength e of an electron and p of a photon of same energy E are related by: e p e p e p 2 e 1/ p The stopping potential for photoelectrons emitted from a surface illuminated by light of wavelength is 3V 0 . When the same surface is illuminated by light of wavelength 2 , the stopping potential is V 0 . The threshold wavelength for the surface is: 4 3 6 8 A radioactive nucleus of mass M emits a photon of frequency and the nucleus recoils. The recoil energy will be: h 2 2 / 2Mc 2 h Mc 2 Zero Which of the following is the correct Einstein's photoelectric equation in terms of stopping potential V 0 and incident wavelength ? V 0 = (hc/e ) - ( /e) V 0 = (h/e ) - V 0 = (hc /e) - V 0 = (hc/e) - ( / ) When a metal surface is illuminated with radiation of wavelength , the stopping potential is V . If the same surface is illuminated with radiation of wavelength 2 , the stopping potential is V/4 . The threshold wavelength for the metallic surface is: 3 4 5 9/4 An electromagnetic wave of wavelength is incident on a photosensitive surface of negligible work function. If the photo-electrons emitted from this surface have the same de-Broglie wavelength d , then: = ( 2mc h ) d 2 = ( 2h mc ) d 2 = ( 2m hc ) d 2 d = ( 2mc h ) 2 The number of photons per second emitted by a 10 kW transmitter at 880 kHz is approximately: 1.7 10 31 1.7 10 25 1.7 10 35 1.7 10 28 When the energy of the incident radiation is increased by 20 % , the maximum kinetic energy of the photoelectrons emitted from a metal surface increased from 0.5 eV to 0.8 eV . The work function of the metal is: 1.0 eV 1.5 eV 0.65 eV 0.3 eV The maximum velocity of an electron emitted by light of wavelength incident on a surface of work function is v . If the wavelength is changed to ' , the maximum velocity becomes 2v . The work function is given by: hc 3 ' (4 ' - ) hc ' ( - 4 ') hc - ' hc + ' Light of wavelength 330 nm is incident on a metal surface. The intensity of light is 5 10 -2 W/m 2 . If 1 % of the incident photons eject photoelectrons, find the number of photoelectrons emitted per second from an area of 1 cm 2 . 8.3 10 11 8.3 10 13 8.3 10 9 8.3 10 15 A photocell is being operated in saturation mode. If the frequency of the incident light is increased, while keeping the intensity constant, the photoelectric current will: Decrease Increase Remain constant Become zero The de-Broglie wavelength of an electron is the same as that of a photon. If v is the velocity of the electron, the ratio of kinetic energy of electron to the energy of photon is: v/2c v/c 2v/c v 2/2c 2 If the wavelength of incident light changes from 400 nm to 300 nm , the change in stopping potential for a given metal will be approximately: 1.03 V 0.54 V 2.10 V 0.31 V An electron and a photon have the same wavelength of 10 -10 m . If E p is the energy of the photon and E e is the kinetic energy of the electron, then: E p > E e E p < E e E p = E e E p = 2E e The work function of a metal is h 0 . If light of frequency 5 u 0 is incident on it, the maximum kinetic energy of the photoelectrons is 4h u 0 . If the frequency of incident light is doubled, the maximum kinetic energy will be: 9h u 0 8h u 0 10h u 0 12h u 0 When a surface is irradiated with light of wavelength , the stopping potential is V 0 . When the same surface is irradiated with light of wavelength 2 , the stopping potential is V 0/4 . The threshold wavelength for this surface is: 3 4 5 /2 3 /2 A 100 W sodium lamp emits yellow light of wavelength 589 nm . Assuming it to be 25 % efficient in converting electrical energy to light, the number of photons emitted per second is approximately: 7.4 10 19 3.0 10 20 1.5 10 18 7.4 10 17 The threshold frequency for a metal is 10 15 Hz . What is the maximum kinetic energy of photoelectrons emitted when radiation of wavelength 2000 is incident on it? 2.1 10 -19 J 6.6 10 -19 J 3.3 10 -19 J 1.0 10 -19 J A photon and an electron have the same energy E . If E is very large compared to the rest mass energy of the electron, the ratio of the momentum of the photon to that of the electron is approximately: 1 2 1/2 2 In a photoelectric experiment, light of frequency is incident on a metal surface. The stopping potential is V 0 . If the frequency is increased to 3 , the new stopping potential V' will be: More than 3V 0 Exactly 3V 0 Less than 3V 0 Exactly V 0/3 The photoelectric threshold wavelength of silver is 3250 10 -10 m . The velocity of the electron ejected from a silver surface by ultraviolet light of wavelength 2536 10 -10 m is approximately: ( h = 4.14 10 -15 eV s , c = 3 10 8 m/s ) 6 10 5 m/s 0.6 10 5 m/s 61 10 3 m/s 0.3 10 6 m/s A point source of light is used in a photoelectric experiment. If the distance between the source and the photocathode is increased by 20 % , the saturation photocurrent will decrease by approximately: 31 % 20 % 44 % 10 % A photon of energy E ejects a photoelectron from a metal of work function . If this electron enters a uniform magnetic field B perpendicularly and moves in a circle of radius r , then r is given by: 2m(E- ) / eB 2mE / eB 2m / eB (E- ) / eB The work function of a metal is 2.5 eV . When light of frequency is incident, the maximum velocity of photoelectrons is v . If the frequency is doubled, the maximum velocity becomes v' . Then: v' > 2 v v' = 2v v' = 2 v v' < 2 v A light of wavelength 4000 is incident on a metal plate. The work function of the metal is 2.5 eV . The maximum velocity of the photoelectrons is approximately: ( m = 9.1 10 -31 kg ) 4.6 10 5 m/s 1.2 10 6 m/s 2.1 10 5 m/s Zero Which of the following graphs correctly represents the variation of stopping potential ( V 0 ) with the intensity of incident light ( I ) for a fixed frequency? A horizontal straight line A straight line passing through the origin A parabola An exponential curve In a photoelectric experiment, when the intensity of incident light is increased, while keeping the frequency constant: The number of photoelectrons increases, but their maximum kinetic energy remains same The maximum kinetic energy increases, but the number of photoelectrons remains same Both increase Both remain same A monochromatic light source of power 200 W emits 4 10 20 photons per second. The wavelength of the light is: ( h = 6.6 10 -34 J s ) 400 nm 500 nm 600 nm 700 nm The maximum kinetic energy of photoelectrons emitted from a surface is K when the incident radiation wavelength is . If the wavelength is reduced to /3 , the new maximum kinetic energy will be: More than 3K Exactly 3K Less than 3K Independent of K A beam of light falls on a metal surface such that photo-electrons are generated. If power of the light source starts to decrease linearly with time t , then variation of the photocurrent I and magnitude of the stopping potential |V| with time is best represented by: Graph (1) Graph (2) Graph (3) Graph (4) A ray of light with wavelength is incident on three different photoelectric cells namely 1, 2 and 3. The threshold wavelength of these photoelectric cells are 1, 2 and 3 , respectively and the magnitude of stopping potentials of these cells are V 1,V 2 and V 3 , respectively. The relation between and threshold wavelengths are 1< , 2> , 3 . The correct option is: V 1=0,V 2<V 3 V 1=0,V 2>V 3 V 1>V 2,V 3=0 V 1<V 2,V 3=0 A metallic surface ejects photoelectrons when hit by green light but not by yellow light. Will it eject photoelectrons for red light? No Yes Only if intensity is high Only if time of exposure is high If the work function of a metal is 5 eV , what is the maximum wavelength of light that can cause photoelectron emission? 2480 Å 1240 Å 4000 Å 6000 Å Which property of light is demonstrated by the photoelectric effect? Particle nature Wave nature Transverse nature Longitudinal nature The slope of the graph between the maximum kinetic energy and the frequency of incident radiation for a metal surface is a universal constant. This constant is: Planck's constant Electronic charge Boltzmann constant Rydberg constant Which of the following graphs represents the variation of the maximum kinetic energy ( K max ) of emitted electrons with the frequency ( ) of incident radiation? A straight line with a negative intercept on the K max axis. A straight line passing through the origin. A parabola opening upwards. An exponential curve. According to Einstein's photoelectric equation, the plot of the maximum kinetic energy of the emitted photoelectrons from a metal vs. the frequency of the incident radiation gives a straight line whose slope: is the same for all metals and independent of the intensity of radiation depends on the nature of the metal used depends on the intensity of the radiation depends both on the intensity of the radiation and the metal used A photon of energy E has momentum p . If the energy of the photon is doubled, then its momentum will be: 2p p/2 2 p 4p Monochromatic light of frequency is incident on a metal surface of threshold frequency 0 . If the stopping potential is V 0 , then the slope of the graph V 0 vs is: h/e e/h h e Which of the following is NOT a characteristic of the photoelectric effect? Emission of electrons occurs after a significant time lag. Threshold frequency depends on the nature of the metal. Maximum kinetic energy is independent of light intensity. The number of emitted photoelectrons is proportional to intensity. The photoelectric effect can be explained by assuming that light: Consists of packets of energy Is a transverse electromagnetic wave Is a longitudinal wave Is a continuous stream of energy A radiation of energy E falls normally on a perfectly reflecting surface. The momentum transferred to the surface is: 2E/c E/c Ec E/c 2 The stopping potential for photoelectrons depends on: Frequency of incident light and nature of surface Intensity of incident light only Distance between the source and metal surface Area of the metal surface Light of wavelength 5000 falls on a sensitive plate with photoelectric work function of 1.9 eV . The kinetic energy of the photoelectrons emitted will be: 0.58 eV 1.24 eV 2.48 eV 1.16 eV The work function of a substance is 4.0 eV . The longest wavelength of light that can cause photoemission from this substance is approximately: 310 nm 540 nm 400 nm 220 nm The slope of the graph between maximum kinetic energy of photoelectrons and the frequency of incident radiation is: h h/e e Work function If the energy of a photon is E , then its momentum is: E/c E/c 2 2E/c E /c A point source of light is used in a photoelectric effect experiment. If the distance of the source from the cathode is doubled, then the saturation photocurrent: Becomes one-fourth Becomes half Remains constant Becomes four times The slope of the graph between stopping potential V 0 and frequency of incident radiation for a metal is: h/e e/h h e The dynamic mass of a photon of wavelength is: h/(c ) h /c hc/ h/c 2 The number of photoelectrons emitted per unit time is directly proportional to: Intensity of incident light Frequency of incident light Wavelength of incident light Stopping potential The dynamic mass of a photon of frequency is given by: h /c 2 h /c hc/ h When a light of wavelength 300 nm falls on a photoelectric emitter, photoelectrons are liberated. For another emitter, light of wavelength 600 nm is sufficient for liberating photoelectrons. The ratio of the work function of the two emitters is: 2 : 1 1 : 2 4 : 1 1 : 4 In a photoelectric experiment, if the intensity of incident light is increased, then: The saturation current increases The maximum kinetic energy of photoelectrons increases The stopping potential increases The threshold frequency decreases If the photoelectric threshold wavelength for a surface is 4000 Å, the work function is: 3.1 eV 2.0 eV 1.1 eV 4.2 eV The energy of a photon of light of wavelength 450 nm is approximately: 2.75 eV 1.50 eV 4.50 eV 3.20 eV A metal has a threshold wavelength of 6000 . Its work function is: 2.07 eV 3.10 eV 1.50 eV 4.14 eV If the energy of a photon is increased by a factor of 4, then its momentum will increase by a factor of: 4 2 16 8 In a photoelectric effect experiment, for a given photosensitive material, the graph of stopping potential ( V 0 ) versus frequency ( ) of incident radiation is a straight line. The intercept of this line on the frequency axis represents: Threshold frequency Work function Planck's constant Saturation current Which of the following statements is true regarding the photoelectric effect? The maximum K.E. of photoelectrons depends only on the frequency of light. The photoelectric current is independent of the intensity of light. The stopping potential increases with increase in intensity. The threshold frequency depends on the intensity of light. The momentum of a photon of frequency is: h / c h c h / c h / c 2 The rest mass of a photon is: Zero Equal to that of an electron Equal to that of a proton Infinity If the momentum of a photon is p , then the frequency of the corresponding radiation is: pc/h ph/c hc/p hp/c A photocathode with work function 2.4 eV is struck by photons of energy 3.5 eV . The stopping potential is: 1.1 V 2.4 V 3.5 V 5.9 V The slope of the graph between the frequency of incident light and the maximum kinetic energy of emitted photoelectrons is: Universal constant Depends on the nature of the metal Depends on the intensity of light Depends on the temperature of the metal The maximum kinetic energy of photoelectrons is 4 eV . What is the stopping potential? 4 V 2 V 8 V -4 V A radiation of intensity I falls on a perfectly reflecting surface. The pressure exerted by the radiation on the surface is ( c is the velocity of light): 2I/c I/c Ic I/c 2 The work function of a metal is W . If light of wavelength is incident, the maximum kinetic energy is K . To increase the maximum kinetic energy to 2K , the incident wavelength should be changed to ' , where: ' < ' > ' = /2 ' = 2 In the photoelectric effect, if the intensity of incident light is increased, the maximum speed of the emitted electrons: Remains constant Increases Decreases First increases then decreases According to the wave theory of light, the kinetic energy of photoelectrons should depend on: Intensity of light Frequency of light Wavelength of light Nature of the surface The maximum kinetic energy of photoelectrons emitted from a surface is 2.0 eV . The stopping potential for these electrons is: 2.0 V 1.0 V 4.0 V 0.5 V A photon of frequency has momentum p and speed c . The wavelength is: h/p p/h c/p h /c If the threshold wavelength for a metal is 0 , then its work function is: hc/ 0 h 0/c c/(h 0) 0/(hc) A photon of frequency has momentum h /c . If it is incident on a perfectly absorbing surface, the momentum transferred to the surface is p 1 . If it is incident on a perfectly reflecting surface, the momentum transferred is p 2 . The ratio p 2/p 1 is: 2 1 1/2 4 Which of the following properties of a photon does NOT change when it enters a different medium? Frequency Wavelength Velocity Momentum Light of energy E falls on a metal of work function E/3 . The ratio of the energy of the incident photon to the maximum kinetic energy of the photoelectrons is: 3:2 2:3 3:1 1:3 The work function of a metal is 1 eV . If a photon of energy 3 eV is incident on it, the maximum velocity of photoelectrons is v 1 . If a photon of energy 5 eV is incident, the maximum velocity is v 2 . The ratio v 2/v 1 is: 2 2 5 / 3 4 If the energy of a photon is equal to the rest mass energy of an electron, then the wavelength of the photon is: ( m e is mass of electron, c is speed of light, h is Planck's constant) h m e c h 2m e c 2h m e c m e c h The dynamic mass of a photon of frequency is: h / c 2 h / c h/( c) Zero The threshold wavelength for a metal is 4000 . A radiation of wavelength 3000 is incident on the metal. The maximum kinetic energy of the photoelectrons is approximately: 1.03 eV 2.10 eV 3.10 eV 0.50 eV In the photoelectric effect, if the intensity of incident light is increased, while keeping the frequency constant: The saturation current increases but stopping potential remains same The saturation current remains same but stopping potential increases Both saturation current and stopping potential increase Both saturation current and stopping potential remain same The momentum of a photon of wavelength 0.01 is: 6.63 10 -22 kg m/s 6.63 10 -24 kg m/s 3.31 10 -22 kg m/s 1.1 10 -23 kg m/s A light source is at a distance r from a photoelectric cell. If the distance is increased to 2r , then the saturation photoelectric current i will become: i/4 i/2 2i 4i In photoelectric effect, the photoelectrons: Are emitted with different speeds up to a maximum value. Are all emitted with the same speed. Are emitted with speeds between zero and infinity. Have speeds that depend only on the intensity of light. The work function of a metal is 2.0 eV . If it is illuminated by light of wavelength 500 nm , what is the maximum kinetic energy of the emitted photoelectrons? ( hc = 1240 eV nm ) 0.48 eV 2.48 eV 0.88 eV No emission occurs When the frequency of incident radiation is increased, what happens to the stopping potential in a photoelectric experiment? It increases linearly with frequency. It decreases linearly with frequency. It remains constant. It increases as the square of the frequency. The energy of a photon is E . Its momentum is p . If the wavelength is reduced by half, the new energy and momentum will be: 2E, 2p E/2, p/2 4E, 4p 2E, p/2 In a photoelectric experiment, if the intensity of incident light is doubled, the maximum kinetic energy of the emitted photoelectrons will: Remain unchanged Be doubled Be halved Increase by four times The work function of a metal is 4.2 eV . If the radiation of photon energy 5.6 eV falls on it, the stopping potential will be: 1.4 V 5.6 V 4.2 V 9.8 V For a given frequency of incident radiation, the stopping potential depends on: The nature of the material of the emitter The intensity of incident radiation The distance between the source and the emitter The potential of the collector Which of the following phenomena supports the particle nature of light? Photoelectric effect Interference Diffraction Polarization In a photoelectric effect experiment, the slope of the graph between the stopping potential and the reciprocal of the wavelength is: hc / e h / e e / hc hc For a photon of frequency , the equivalent mass is: h / c 2 h / c h / (c ) h c 2 A photoelectric cell is illuminated by a small bright source of light placed at a distance d . When the same source of light is placed at a distance 2d , the number of electrons emitted per second is: Reduced to one-fourth Reduced to half Doubled Quadrupled If a photon has velocity c and frequency , then which of the following represents its wavelength? c/ /c h /c 2 h /c Which of the following values of the work function is most likely for an alkali metal like Cesium? 2.1 eV 4.5 eV 6.2 eV 10.0 eV The threshold frequency for a metal is 0 . When light of frequency 4 0 is incident on the metal, the maximum kinetic energy of the photoelectrons is K 1 . When light of frequency 3 0 is incident, the maximum kinetic energy is K 2 . The ratio K 1/K 2 is: 1.5 2.0 0.75 3.0 In the photoelectric effect, if the intensity of incident monochromatic light is increased, which of the following remains unchanged? Maximum kinetic energy of photoelectrons Saturation current Number of photons incident per unit time Rate of emission of photoelectrons The number of photons emitted per second by a 100 W sodium lamp (wavelength 589 nm ) is approximately: 3 10 20 3 10 18 1.5 10 20 6 10 20 What is the momentum of a photon having an energy of 3 eV ? 1.6 10 -27 kg m/s 4.8 10 -27 kg m/s 1.1 10 -27 kg m/s 9.1 10 -31 kg m/s The work functions for metals A, B and C are respectively 1.92 eV , 2.0 eV and 5 eV .