Photoelectric Effect Questions and Answers

Maximum kinetic energy of emitted electron depends on frequency of incident photon when frequency of incident photons is Equal to threshold frequency Half of threshold frequency Greater than threshold frequency One third of threshold frequency

Illustration 3 6 A plate of mass 10 g is in in air due to the force exerted by equilibrium a light beam on the plate Calculate power of the beam Assume that the plate is perfectly absorbing 111 Fig 3 8

The rest energy of an electron is 0 511 MeV The electron is accelerated from rest to a velocity 0 5 c The change in its energy will be 1 0 026 MeV 2 0 051 MeV 3 0 079 MeV 4 0 105 MeV

Consider a plane electromagnetic wave propagating in free space and having an electric field distribution given by 3 2 4 0 1 0 1 E E ax ay 2 2 where E and a are constants Calculate the corresponding magnetic field R

If min is minimum wavelength produced in X ray tube and is the wavelength of K line As the operating voltage is increased A B C Ky increases 7 K decreases K min increases

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 AIPMT 2014 1 0 65 eV 2 1 0 eV

A 200 W sodium street lamp emits yellow light of wavelength 0 6 m Assuming it to be 25 efficient in converting electrical energy to light the number of photons of yellow light it emits per second is AIPMT Prelims 2012 2 3 1019 4 6 1018 1 62 1020 3 1 5 1020

Monochromatic radiation emitted when electron on hydrogen atom jumps from first excited to the ground state irradiates a photosensitive material The stopping potential is measured to be 3 57 V The threshold frequency of the material is 1 1 6 x 1015 Hz 3 4 x 1015 Hz AIPMT Prelims 2012 2 2 5 x 1015 Hz 4 5 x 1015 Hz

1311 is an isotope of lodine that decays to an isotope of Xenon with a half life of 8 days A small amount of a serum labelled with 131 is injected into the blood of a person The activity of the amount of 131 linjected was 2 4 x 105Becquerel Bq It is known that the injected serum will get distributed uniformly in the blood stream in less than half an hour After 11 5 hours 2 5 ml of blood is drawn from the person s body and gives an activity of 115 Bq The total volume of blood in the person s body in liters is approximately you may use et 1 x for x 1 and In 2 0 7

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Electromagnetic radiation whose electric component varies with time as E C C C3coswt coswot here C C and C3 are constants is incident on lithium and librates photoelectrons If the kinetic energy of most energetic electrons be 0 592 10 19 J Given that wo 3 6 10 5 rad s and w 6 x 1014 rad s What is the work function of lithium in eV take planks constant h 6 6 10 34 MKS

When the light of frequency 2vo where vo is threshold frequency is incident on a metal plate the maximum velocity of electrons emitted is v When the frequency of the incident radiation is increased to 5vo the maximum velocity of electrons emitted from the same plate is v The ratio of v to v is NEET 2018 1 1 2 3 2 1 2 1 4 4 4 1

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 x 10 10 m is Given h 4 14 x 10 15 eVs and c 3 x 108 m s 1 NEET 2017 1 6 x 105 m s 1 2 0 6 106 m s 1 3 61 x 10 m s 1 4 0 3 x 106 m s 1

Which of the following relations between the particle number density n and temperature T must hold goc for a gas consisting of non interacting particles to be described by quantum statistics a n T l c n T3 2 1 b n T3 1 d n T1 2 and n T2 can have any value

5 A ray of light travelling in a transparent medium falls on a surface separating the medium from air at an angle of incidence of 45 The ray undergoes total internal reflection If n is the refractive index of the medium with respect to air select the possible value of n from the following 1 1 2 3 1 4 2 4 3 4 1 5

2 b State the schematic plots for each of following cases of photoelectric effect i Photoelectric current vs potential difference for two different intensities of UV light ii Maximum photoelectron kinetic energy us frequency of incident UV light for two different metal surfaces having different work functions 4

A mono chromatic lightwave moves from one transparent medium to another The refractive index of the second medium is thrice the refractive index of the first medium If the wavelength of light in first medium is 6 x 10 7 m then the wave length of the lightwave in second medium would be 1 1 x 10 7m 2 2 x 10 7 m 4 18 x 10 7m 3 9 x 10 7 m

9 If E and P are the energy and the momentum of a photon respectively then on reducing the wavelength of photon 1 P and E both will decrease 2 Pland E both will increase 3 P will increase and E will decrease 4 P will decrease and E will increase

The threshold frequency for photoelectric emission in Cu is 1 1 10 5 s Find the maximum energy of photoelectrons when light of frequency 1 5 10 5 s falls on Cu surface also calculate the retarding potentiall

Which of the following equations is relativistically invariant a B Y and 8 are constants of suitable dimensions 2 x 1 t 2 x 1 x x 1 ap x 1 di x Y b d a x 1 x t B di ap x 1 t 8 x x 1 x

A pion rest mass m 135 MeV c is moving with a velocity v 0 8c2 If it decays by emitting two photons both of which move in z direction find their energies and frequencies in units of MeV and MeV h respectively

16 Photoelectric effect experiments are performed using three different metal plates p q and r having work function Op 2 0 eV q 2 5 eV and o 3 0 eV respectively A light beam containing wavelengths of 550 nm 450 nm and 350 nm with equal intensities illuminates each of the plates The correct I V graph for the experiment is Take hc 1240 eV nm IA a c P 9 r r 9 P V V b d 14 14 V IZ

V When radiation of the wavelength is incident on a metallic surface the stopping potential is 4 8 volt If the same surface is illuminated with radiation of double the wavelength then the stopping potential becomes 1 6 volt Then the threshold wavelength for the surface is a 22 b 42 c 62 d 82

experiment graph of stopping 1 is drawn Nature 21 In photoelectric potential versus Wavelength and reciprocal of slope of graph will be hc 1 Straight line e 2 Rectangular hyperbola C 3 Straight line e slope he M e hc Ve VR 1 X 26 For nuclear nucleus z My are the reaction na 1 Negati 2 Positiv 3 Nega 4 Posit 27 Consider following

A photon of wavelength is scattered from an electron which was at rest The wavelength shift A is three times of and the angle of scattering is 60 The angle at which the electron recoiled is p The value of tan is electron speed is much smaller than the speed of light 1 0 28 2 0 22 3 0 25 4 0 16

JJ SCIENCE ACADEMY A photon of green light of wavelength 5500 is incident on a photo emitter of work function 1 2 eV The minimum de broglie wavelength of the photoelectron will be 1 12500 A 2 12 3 A 3 1 6 A 4 5500 In a CE amplifier the collector current changes by 100 mA when the base current changes by 100 A If

Identify the wrong statement 1 The electrical potential energy of a system of two protons shall increase if the separation between the two is decreased 2 The electrical potential energy of a proton electron system will increase if the separation between the two is decreased 3 The electrical potential energy of a proton electron system will increase if the separation between the two is increased 4 The electrical potential energy of system of two electrons shall increase if the separation between the two is decreased 5

BPH2101 PHYSICS REMAINING TIME HOURS MINUTES SECONDS 1 48 49 31 The output of a laser has pulse duration of 30 ms and average output power of 1 W per pulse How much energy is released per putse it wavelength is 6600 A 0 003 00 002 00 004 00001

If K and K are maximum kinetic energies of photoelectrons emitted when lights of wavelength and 2 respectively incident on a metallic surface If 3 2 then A B C D K K 3 x 2 K 3 K 3K K 3K1

de Broglie wavelength of an electron accelerated by a voltage of 50 V is close to el 1 6x10 C m 9 1x10 kg h 6 6x10 4 Js 00 C 0 5 A 1 2 A 1 7 A

In Moseley s law for characteristic X rays is vv a Z b skipped B C D both a and b are independent of the material only a depends on material only b depends on material both of a and b depend on the material

During charging a capacitor variations of potential V of the capacitor with time t is shown as skipped Jury 6 7

When light of wavelength 800A illuminates a metal the most energetic photoelectron emitted can just ionise the hydrogen atom in ground state What is the work function of the metal approximately 1 1 2 eV 2 1 9 eV 3 3 4 eV 4 4 8 eV

AIPMT 2008 The work function of a surface of a photosensitive material is 6 2 eV The wavelength of the incident radiation for which the stopping potential is 5V lies in the 1 Infrared region 3 Ultraviolet region AIPMT NEET 2 X ray region 4 Visible region AIPMT 2009 MP0070

MT 2006 A photo cell employs photoelectric effect to convert 1 Change in the frequency of light into a change in electric voltage 2 Change in the intensity of illumination into a change in photoelectric current 3 Change in the intensity of illumination into a change in the work function of the photocathode 6 4 Change in the frequency of light into a change in the electric current AL The work functi material is 6 2 radiation for w in the 1 Infrared r 3 Ultraviole F

e in a change MP0064 When photons of energy hv fall on an aluminium plate of work function Eo photoelectrons on maximum kinetic energy K are ejected If the frequency of the radiation is doubled the maximum kinetic energy of the ejected photoelectrons will be 2 2K 1 K Eo 3 K 4 K hv 7 traviolet region 2 X ray regio 4 Visible rec AIPMT 2009 The number of photo electrons emi a frequency v higher than the thre v is proportional to 1 Frequency of light v 2 v Vo 3 Threshold frequency v 4 Intensity of light MP0065 The momentum of a photon of energy 1 MeV in kg 8 Monochromatic light alium

4 5 Quantum efficiency n number of electrons emitted per second Quantum efficiency total number of photons incident per second nph X n nph If quantum efficiency is x then n 6 Photoelectric current i X 100 n from equation i ph Here n 5 x 1024 J m P ph OBECTIC EFFECT

05 Monochromatic light of wavelength 400 nm and 560 nm are incident simultaneously and normally on double slits apparatus whose slits separation is 0 1 mm and screen distance is 1m Distance between areas of total darkness will be a 4mm b 5 6mm c 14mm d 28mm

If the concentration of free electrons in a metal object equals 1 102 electrons m Determine the temperature at which two percent probability that an energy level of 7 73eV is empty O O O O O O O 334 15K 330 11K 340 22K 337 15K O 344 15K 322 15K

3 100 kg 4 100 gm Wavelength of n neutron at temperature 27 C is 6 A Its wavelength at 927 C will be 1 A 2 2X 3 4 10 gm of ice at 20 C is added to 10gm of water at 7 3 100 kg and 1 A 27 C 27 C 2 2X 4 100 gm 2010 m

The peak emission from a black body at a certain temperature occurs at a wavelength of 6000A On increasing its temperature the total radiation emitted is increased to 16 times These radiations are allowed to fall on a metal surface Photoelectrons emitted by the peak radiation at higher temperature can be bought to rest by applying a potential equivalent to the excitation potential corresponding to the transition for the level n 4 to n 2 in the Bohr s hydrogen atom The work function of the metal is O eV a given by 100 where is the umerical constant The value of is found out to be 3p find the 0

When a metallic surface of threshold wavelength 4X is illuminated with light of wavelength X the stopping potential is V When the same surface is illuminated by the light of wavelength 2X stopping potential is Threshold wavelength for the metallic surface is A B C V 2 2V V 3 Correct Answer

we have a ne 44 25 5 Example 2 Electrons of energy 10 eV are incident on a potential step of height 13 8 eV Find the distance in which the probability density of finding the particle decreases to a factor of 0 01 as it penetrates into the FOR LEH classically forbidden region PARCER ENDEAVOUR U

iii What is the need to achieve population inversion a To excite most of the atoms b To bring most of the atoms to ground state c To achieve stable condition d To reduce the time of production of laser

A clean surface of a metal in a vacuum tube is irradiated with a monochromatic light of wavelength 500nm and the resulting photoelectric current is measured by the ammeter A as shown in the circuit It is found that it the voltmeter V reading is greater than 0 8V the ammeter shows zero reading Now with a second source of light the ammeter reading vanishes when the voltmeter regarding is changed to 1 2 V Then Battery B with rheostat R makes a potential divider circuit wwwwwwwwww 500m Given h 6 6x10 Jsc 3x10 ms e 1 6x10 C A The frequency of second source is 6 97x10 Hz B The kinetic energy of photoelectrons due to first source is less than or equal to 08 eV C The work function of emitting surface is 1 68eV D The kinetic energy of photoelectrons due to second source is 1 2 eV

If work function of a metal is 3 eV and wavelength of subjected radiation to the metal is 275 nm Then the de Broglie s wavelength in A of photoelectrons emitted by the metal is nearly n Value of n rounded off to nearest integer is Given hc 1240 eV nm

Which of the following figures represent the variation of particle momentum and the associated de Broglie wavelength o P 2

xplain the absorption process in LASER Derive the mathematical expression for Einstein s Co efficient and its significance 3 7 Once you upload files from your second device click on Sync to check your o Camera

The activity of a radioactive sample moving with velocity V is given by R R o e 2t A detector at a distance from the sample detects number of counts per second If the count number detected by the counter remains constant what is the speed of the sample

A photo sensitive plate p 1 2 eV is placed at 200 cm from a point source of light of 4 8 x 10 7 m and a power output of 1 0 W The light falls nearly normally to the plate Assuming the photon efficiency of plate to be 0 05 Use Area of plate 0 25 m Choose correct statement Photon flux is 2 4 10 6 Photon flux is 4 8 x1016 Photoelectric current is 9 6 x10 7 A Photoelectric current is 4 8 10 7 A