Photoelectric Effect Questions and Answers

Threshold wavelength for photoelectric emission from a metal surface is 5200 A Photoelectrons will be emitted when this surface is illuminated with monochromatic radiation from 1 1 W IR lamp

Photoelectric effect is observed from a metal surface when light of frequencies 3x10 4 Hz and 2x10 4 Hz is incident If the maximum kinetic energies of the photoelectrons are in ratio 2 1 then for which of the following frequencies photoelectrons are emitted from the same metal plate A 10 Hz 10 4 Hz B C 10 Hz D 4 10 4 Hz

In a photelectric experiment measurement s hows that all the ejected electrons have nonz ero kinetic energy What can you say about th e photelectric current 1 Photo electric curr ent is decreasing 2 Cannot predict the state of photoelectric current 3 Photelectric curre nt is increasing 4 Photelectric current is sat

In a Compton experiment the frequency of an incident photon is 5 1016 Hz Calculate the de Broglie wavelength of the scattered electron when the scattering angle of the photon is a 90 and b 180

If total energy transferred to a surface in time t by electromagnetic waves is U then magnitude of tota momentum delivered to this surface for complete absorption is P 00 2U OP 200 P UC

experiment measurement shows that all the ejected electrons have nonzero kinetic energy What can you say photelectric current about the Cannot predict the state of photoelectric current Photelectric current is saturated Photo electric current is decreasing

10 The stopping potential for photoelectrons ejected from a photosensitive material d function 1 6 eV when it is radiated by photons of energy 2 4 eV is 10 A og y RI 80

The visible spectrum of electromagnetic wave approximately which spans between 300 nm to 800 nm falls on a metallic surface The work function for this metallic surface is 2 40 eV Find the followings a The spectral range that will successfully eject photoelectrons from the metallic surface b The speed of the ejected electrons

5 Plates A and B are a part of a photoelectric cell bearing a separation of 5 cm between each other The plates are connected through a galvanometer in absence of any cell For this combination illumination of wavelength 3000 Angstrom and 5000 Angstrom are incident on plate B carrying a work function of 2 59 eV The magnetic field B is uniformly existing in space then the minimum value of B for which the galvanometer shows zero deflection will be A 13 22 X 10 5 T B 24 22 X 105 T C 3 02 X 10 5 T D 8 3 X 105 T

31 The angular momentum of an electron in the nth orbit is given by 1 nh 2 h 2m 3 nh a 4 n h

3 The given graph shows the variation of frequency of incident radiation with the maximum kinetic energy of the electrons emitted from the surface of photo sensitive material Kmax V Which of the following statements is are true about the graph a Slope of the graph gives the value of Planck s constant b Intercept on the negative Kmax axis gives the value of work function c The maximum kinetic energy of emitted electrons depends on the intensity of incident radiation d Both a and b

SolveLancer Test Which of the following statement is incorrect 1 Kg emission has higher wavelength and energy than k II First line of Lyman series has energy times energy of first line of Balmer series both for H atom 27 5 III For a free H atom during emission of photon momentum of H atom does not change IV If on e of energy 10 3eV is collides of with stationary H atom then excitation of e takes places from n 1 to n 2 in H atom SolveLancer Test a I IV b III IV c I II III d I III IV

Example 7 A tiny glass sphere of mass 10 8 g and 0 02 mm diameter can be kept floating in mid air supported only by a beam of laser light directed upward What is the irradiance intensity necessary to do that

When radiation of wavelength A is incident on a photo sensitive metallic surface the stopping potential is 3 6 volt If the same surface is illuminated with radiation of double wavelength then the stopping potential becomes 1 2 V Then the threshold wavelength of the metal surface is O 4 O 2A OX O 3

Observe the current v s voltage graphs of two photocells receiving same intensity of a monochromatic beam You may consider the plate area receiving the light to be same Now choose the correct statement s Photo Current 2 1 Anode Potential A Photoelectric efficiency of 2 must be greater than 1 B photoelectric efficiency of 2 may be greater than 1 C Work function of 2 must be greater than that of 1 D Work function of 2 must be less than that of 1

Example 8 The potential energy of a simple harmonic oscillator of mass m and oscillating with an angular frequency w is V x mw x a Write the Schr dinger equation for the oscillator b Calculate the energy eigenvalue in the ground state if the corresponding eigen function be 40 mw h 1 4e a x 2 where a mw h soy 10tolline

A photo electric cell is shown in the figure The emitter plate cathode is made of copper o 4 7 eV and emitter is illuminated by a source of monochromatic light of wavelength 200nm Saturation current is observed when potential difference between cathode and anode is 1V and anode at higher potential Range of ammeter is large Take he 1240 ev nm 1 II Cathode Anode 0 5V 1V List I Minimum kinetic energy of photoelectrons reaching the collector is Maximum kinetic energy of photoelectrons reaching the collector is If only S is closed then A I S II R III Q IV S C IT II P III S IV U S S III If wavelength of incident light is decreased no of incident photon same then reading of current as shown by ammeter will IV If number of incident photons increases then reading of current as shown by ammeter will A List II P 2 5 eV Q Remain same R 1 eV S Increase T O U Decrease B I P II T III R IV S D I R II P III Q IV S

4 A photon collides with a stationary hydrogen atom in ground state inelastically Energy of the colliding photon is 10 2 eV After a time interval of the order of microsecond another photon collides with same hydrogen atom inelastically with an energy of 15 eV What will be observed by the detector

Example 5 A crystal has some negative ion vacancies each containing one electron Treat these electrons as moving freely inside a volume whose dimensions are of the order of lattice constant Assuming the value of lattice constant estimate the longest wavelength of electromagnetic radiation absorbed by these electrons

d Tangent to the electric field at every point e Equal to the electric field at every point Problem 11 Show Work to get credit 15 points To start a car engine the car battery moves 4 87 x 1021 electrons through the starter motor How many coulombs of charge were moved

In the photoelectric effect current is produced immediately even with dim light This implies that a electrons need time to absorb energy in order to be ejected Ob electrons do not need time to absorb energy in order to be ejected Oc electrons are constantly being ejected d electrons are not being ejected

14 Given a photon with wavelength 520 nm find the energy and momentum of the photon What equivalent mass would a particle have if all the energy of the photon were converted to mass A 4

initially contain equal number of nuclei X has a half life of 1 hour and Y has a half life of 2 hours After two hours the ratio of the activity of X to the activity of Y is A B C D 1 4 N N 1 2 Your Answer 1 1 Correct Answer 2 1 EXPLANATION No No 4

1 Photons of energy of 6 eV are incident on a metal surface whose work function is 4 eV The minimum kinetic energy of the emitted photo electrons will be Gev 4 A 0 eV C 2 eV B 1 eV D 10 eV M P C E E T 2001

Q9 What is the frequency associated with a photon of energy 3 3 10 10 J Given h 6 626 10 34 Js ans 5 10 23Hz Q10 Light of wavelength 5000 falls on a sensitive plate with work function 1 90eV Calculate a energy of the photon in electron volt and b kinetic energy of the emitted photoelectrons Given h 6 626 10 34 Js ans a 2 48eV b 0 58 eV

In relativistic mechanics m fefTm equivalent relation in electricity for electric charge is af 1 q 90 3 90 9 2 mo mo 2 q 4 q a grea the 90 1 3 qov C

Q 110 What is the stopping potential for photo Q 110 1 2 eV in Grafi icdaci fax Prich fand aur electrons ejected from a metal of work function 1 2 eV when the incident light consist of photons of energy 1 8 eV 1 8 eVicia Buftera 1 0 6 V 3 1 8 V 2 1 2 V 4 2 4 V 1 0 6 V 3 1 8 V 2 1 2 V 4 2 4 V

When radiation of wavelength is incident on a photo sensitive metallic surface the stopping potential is 3 6 volt If the same surface is illuminated with radiation of double wavelength then the stopping potential becomes 1 2 V Then the threshold wavelength of the metal surface is 1 42 3 2 2 4 32

A positron a proton and an a particle are accelerated from rest by same potential A difference If ep and a are their respective de Broglie wavelengths then which of the following is correct a 1 e p a Ae a 2 e 2p 3 e p a P

Beam of light of wavelength incident on a photosensitive work function 2 eV Maximum kinetic 200 nm is surface of energy of photoelectron is 1 6 2 eV 2 2 eV 3 4 2 eV 4 Zero

Work function of a metal surface is 2 eV When light of frequency is incident on the surface maximum kinetic energy of photoelectrons emitted is 5 eV If the frequency of the incident light is increased to 4v then the maximum kinetic energy of photoelectron emitted will be Only one correct answer A B C 20 eV 22 eV 26 eV i

An electron in an atom makes transition from the energy state E E to E 1 5 E The wavelength of the emitted photon is Only one correct answer A B C 2hc hc E 2hc 3E

If the radiations of wavelength 200 nm and nm are incident on a substance of work funct 2 eV one by one then the ratio of the stopp potentials for the emitted photoelectrons will approx 1 2 1 3 4 1 2 1 2 4 1 3

In the circuit shown in figure if the diode forward voltage drop i then the voltage difference between A and B is 5 KQ 5 kn www www B A 0 2 mA O 1 3 V O 0 5 V O 2 3 V O Zero

O In an experiment on photoelectric effect photons of wavelength 300 nm eject electron from a metal of work function 2 25 eV A photon of energy equal to that of the mo energetic electron corresponds to the following transition in the hydrogen atom A n 2 to n 1 state C n 3 to n 2 state B n 3 to n 1 state D n 4 to n 3 state

Consider a hypothetical annihilation of a stationary electron with a stationary positron What is the wavelength of resulting radiation 1 2 3 4 h 2moc h moc 2h moc h 3 1 3 2 1 4 3 9 2 8

In a photelectric experiment measurement shows that all the ejected electrons have nonzero kinetic energy What can you say about the photelectric current Photo electric current is decreasing Cannot predict the state of photoelectric current Photelectric current is increasing Rhotelectric current is saturated

transmitted into radiation and went into one quantum 12 Calculate the De Broglie wavelength associated with an electron of energy 5 Me m 9 1x10 kg h 6 62 10 Js 2 4x9x10 m 13

12 In the diagram shown a uniform electric field E has been applied along the width of the two parallel metal plates The work function of the metal plates is hf and the incident light has photons of energy 2hf What would be the stopping potential in this set up A hf eEL e B hf eEL e C hf eEL1 e D hf eEL e Photon

If energy of incident photon is increased by 30 then the kinetic energy of photoelectrons ejected from the surface is increased from 0 2 eV to 0 85 eV The work function of the metal is nearly equal to 2 1 97 eV 4 2 34 eV 1 1 32 eV 3 2 42 eV

9 Observe the current versus voltage graphs of two photocells receiving same intensity of a monochromatic beam You may consider the plate area receiving light to be same Which of the following statements is are true 1 Photoelectric efficiency of 2 is greater than 1 II Photoelectric efficiency of 1 is greater than 2 III Work function of 2 is greater than 1 IV Work function of 1 is greater than 2 B I III C II IV A I IV Photocurrent D None 2 1 anode potential

11 Photons corresponding to the first five transitions of Balmer series are incident on a metal plate which has work function 3eV What will the number of photoelectrons emitted if corresponding to each wavelength the number of photons available are equal to N Consider one electron to be emitted for every single photon A N B 2N C 3N D 4N

67 Two batteries one of emf 18 V and internal resistance 2 Q and the other of emf 12 V and internal resistance 1 2 are connected as shown The voltmeter V will record a reading of 1 15 V 3 14 V 1921 201 12 V 18 V harge 62 AIPMT Prelims 2005 2 30 V 4 18 V

In a photoelectric experiment set up photons of energy 5 eV falls on the cathode having work function 3 eV i If the saturation current is i 4 A for intensity 105 W m then plot a graph between anode potential and current ii Also draw a graph for intensity of incident radiation 2 x 10 5 W m X rays are incident on a target metal atom having 30 neutrons The ratio of atomic radius of the targe

Light of intensity 10 5W m falls on a sodium photocell of surface area 2cm Assuming that top 5 layers of sodium absorb the incident energy the estimated time required for photoelectric emission considering wave model of light is approximately givenp 0 971gm cc mass 23gm mol work function 2eV Atomic number 11 ERPAD

E 2c V 1 Eph Ee 2 Eph 2C 3 Pph 4 Pe Pph ph 2V is n If the distance between the soruce and the cell is doubled then the number of photoelectrons emitted A source of light is at a distance d from a photocell and the number of photoelectrons emitted from the cell 2 n 4 3 n 8 1 n 2 4 4n nhoton of energy 4eV is incident on a metal surface whose work function is 2eV The minimum reverse 1 ud for stopping the emission of electrons is

A positron of 1MeV collides with an electron of 1 MeV and gets annihilated and the reaction produces two y ray photons If the effective mass of each photon is 0 0016 amu then the energy of each y ray photon is about 1 1 5 MeV dem 4 2 MeV t 2 3 MeV 3 6 MeV

The stopping potential for electrons emitted from a photosensitive surface illuminated by light of wavelength 491 nm is 0 710 V When the incident wavelength is changed to a new value the stopping potential is 1 43 V The new wavelength is 1 329 nm 3 82 2 309 nm 1 100

Light with an energy flux of 6 W cm2 falls on a non reflecting surface at normal incidence If surface has an area of 50 cm What total momentum transferred in one minute the surface for complete absorption NCERT Pg 27 2 3 x 10 5 kg m 4 6 4 kg m s 1 6 x 10 5 kg m s 1 3 2x 10 5 kg m s 1

Photons of wavelength y are incident on a metal The most energetic electrons ejected from the metal are bent into a circular arc of radius R by a perpendicular magnetic field having a magnitude B The work function of the metal is where symbols have their usual meanings A B C he hc ms hc he B R 2me eBR 2me 2me mec 2 e B R2 2me G QUESTION 1 6 Correct 0 2 7 MY PERFOR SCORE