Photoelectric Effect Questions and Answers

In a hydrogen like atom electron makes transition from an energy level with quantum number n to another with quantum number n 1 If n 1 the frequency of radiation emitted is proportional to 2013 Main a c n 1 n b d n 2 n 3

a the magnitude of b its kinetic energy in joule and in electron volt 14 Find de Broglie wavelength corresponding to the root mean square velocity of hydrogen molecules at room temperature 20 C baldua d state It has a total energy of 3 4 eV find the 070

29 In the arrangement shown in figure 42 E4 y 10 mm d 0 24 mm and D 12 m The work function of the material of the emitter is 2 2 eV Find the stopping potential V needed to stop the photocurrent Bright Dark Bright Dark Bright Ty Ho S M A any naturnoo

3 hv A metal surface of work function 1 07 eV is irradiated with light of wavelength 332 nm The retarding potential required to stop the escape of photo electron is 1 4 81 eV 3 2 66 eV 2 3 74 eV 4 1 07 eV Light of wavelength 3000 A is incident on this metal surface The velocity of

Light from a monochromatic source is incident normally on a small photo sensitive surface S having work function If power of the source is W and a is the distance between the source and S then A the number of photons striking the surface per unit time will be 1 B the maximum energy of the emitted electrons will be hc 26 2 WAS 4thca 1 C the stopping potential needed to stop the most energetic photons will be e hc D photo emission occurs only if 0 x hc 26

663 mW of light from a 540 nm source is incident on the surface of a metal If only 1 of each 5 x 10 incident photons is absorbed and causes an electron to be ejected from the surface Find the tota photocurrent in the circuit

3 The kinetic energy of the fastest moving photo electron from a metal of work function 2 8 eV is 2eV Calculate the value of kinetic energy if the frequency of the light is doubled Ans 6 8 eV of Ans 6 57 x We have E P

c p d Both p and E decrease photoelectrons a inversely with the intensity and is independent of the frequency of the incident radiation b inversely with the frequency and is independent of the intensity of the incident radiation c linearly with the frequency and the intensity of the incident radiation 5 The maximum kinetic energy of the varies d linearly with the frequency and is independent of the intensity of the incident radiation

intensity of the 6 If the particles listed below all have the same kinetic energy which one would possess the shortest de Broglie wavelength a Deuteron c Proton b a particle d Electron

c a particle The energy that should be added to an electron t reduce its de Broglie wavelength from 1 nm to 0 5 nr 2005 is a four times the initial energy b equal to the initial energy c twice the initial energy d thrice the initial energy

3 h The work function of a certain metal is 2 3 eV If light of wave number 2 x 106 m 1 falls on it the kinetic energies of fastest and slowest ejected electron will be respectively 2 0 18 eV zero 4 0 18 eV 0 18 eV mognetic radiations of frequenc 1 2 48 eV 0 18 eV 3 2 30 eV 0 18 eV

10 From the photoelectric effect we may infer correctly that KEA 71 1 Na and Al both have the same threshold frequency 2 Maximum kinetic energy for both the metals depend linearly on the frequency 3 The stopping potentials are different for Na and Al for the same change in frequency from their respe threshold frequency 4 Al is better photosensitive material than Na WAVE NATURE OF MATTER

44 Consider a hydrogem like atom whose energy in 13 6Z2 2 n th n state is given by En When this excited atom makes a transition from excited state to ground state most energetic photons have energy Emax 52 2224 eV and least energetic photons have energy Emin 1 224 eV The atomic number of atom is a 2 c 4 b 5 d 3 5 30

If the wavelength of incident light changes from 4000 to 3100 change in stopping potential will be 0 35 V 0 9 V 0 40 V 0 1 V

If photoelectric electrons are ejected from metals X and Y by light of frequency f the potential difference V required to stop the electrons is measured for various frequencies If Y has a greater work function than X which graph illustrates the expected results 4 V V X V 3 2 0 0 1 0 0 0 0

A light beam of intensity 20 W cm is normally normally on a perfectly incident reflecting surface of sides 25 cm x 15 cm The momentum imparted to the surface by the light per second is A 1x 10 5 kg ms 1 B 5 x 10 5 kg ms 1 P 21 C 1 2 x 10 5 kg ms D 2 x 10 5 kg ms 2x20 7x10

5 A 75 W light source emits light of wavelength 600 nm a Calculate the frequency of the emitted light b How many photons per second does the source emit

0 Across a photoelectric cell a source of variable potential difference is connected and the photoelectric current is plotted against the applied potential difference The graph in broken lines represents a curve of current vs applied potential difference If the frequency is increased and the intensity is reduced the curve which may now represents the situation is 1 A AI 0 0 2 B B C D 3 C V 4 D

A point source of light is placed at the centre of curvature of a hemispherical surface The radius of curvature is r and the inner surface is completely reflecting Find the force on the hemisphere due to the light falling on it if the source emits a power W

2 Show that it is not possible for a photon to be completely absorbed by a free electron

6 Which of the graphs shown below does not represent the relationship between incident light and the ejected from metal surface JEE Mains online 20 Number of electrons K E of electrons 0 0 Frequency of Light Frequency of Light K E of electrons K E of electrons 0 Intensity of Light Energy of Light

16 Maximum kinetic energy of a photoelectron is E when the wavelength of incident light is If becomes four times when wavelength is reduced to one third then work function of the energy metal is 3 hc a c 2 he b d hc 32 hc 22

10 kg ms 2013 The wavelength of the first spectral line in the Balmer series of hydrogen atom is 6561 A The wavelength of the second spectral line in the Balmer series of singly ionized helium atom is A 1215 A C 2430 A B 1640 A D 4687 A 2011 A

Consider a source emitting 100 W of green light at a wavelength of 500 nm The number of photons emerging from source per second is 1 2 5 10 9 photon per second 2 25 1020 photon per second 3 25 x 10 9 photon per second 4 25 x 10 7 photon per second

3 An electron of mass m when accelerated through a potential difference V has de Broglie wavelength The de Broglie wavelength associated with a proton of mass M accelerated through the same potential difference will be 1 2 3 m M m 2 4 2 MX

D The diagram shows the energy level for an electron in a certain atom In which transition the energy emission is maximum 1 I 2 I 3 III IV n 4 n 3 n 2 n 1

Figure shows the graph of stopping potential versus the frequency for a photosensitive metal The plank s constant and work function of the metal are 1 2 4 V 2 K V V V V V2 e V V V V2 V V1 V V e V 2 3 V V V e V V V v V v V V e V V1 V V1 e e a V V V v V V e

1 When a point source of monochromatic light is at a distance of 0 2 m from a photoelectric cell the cut off voltage and the saturation current are 0 6 volt and 18 mA respectively If the same source is placed 0 6 m away from the photoelectric cell then 1 The stopping potential will be 0 2 V 2 The stopping potential will be 0 6 V 3 The saturation current will be 6 mA 4 The saturation current will be 18 mA

A point source of light of power 3 2 milli watts emit energy 5eV If the source is located at a distance of 0 8m from the centre of metallic sphere of work function 3 eV and radius 8mm Number of photoelectrons emitted in 1 sec if efficiency is 1 is x x 10 in significant number then find value of y 1eV 1 6 x 10 9 J

19 Calculate the energy radi minute by a blackbody of surface area 100 cm when it is maintained at 227 C 25

The electric field at a point associated with light wave is given by E Eosin 2xftsin 2xfl whose work function is The velocity of fastest moving photoelectron ermitted will be where f and f are two different frequencies f f If this light wave is incident on a metal hf 4 Vm 0 1 5 41 A hf 4 m 2 Vm h 1 1 4 B platy

8 The ratio of frequencies of incident photons in V2 the graph shown will be K max 8 evt eV 7 eV 5 eV 6 eV V V2 v Hz

distance between source and The wavelength of photons in two cases are 4000 and 3600 respectively what is difference potential for these two

When a metal is irradiated by monochromatic light the maximum kinetic energy of the photo electrons 1 2eV If frequency of the light is increased 50 then maximum kinetic energy of photo electron is 3 6 Evaluate the workfunction of the metal

A 1 milliwatt laser source is emitting light of wavelength 555 nm The number of photons emitted per second are approximately Planck s constant 6 6 10 34 m Kg s B 1011 D 1018 A 107 C 1015

3 A and B are two metals with threshold frequencies 1 8 x 10 4 Hz and 2 2 x 1014 Hz Two identical photons of energy 0 825 eV each are incident on them Then photoelectrons are emitted by Taking h 6 6 x 10 34 J s begge as low as 3 2012 a Balone c Neither A nor B b A alone d Both A and B

21 A radioactive nucleus of mass M emits a photon of frequency v and the nucleus recoils The recoil energy will be AIPMT Prelims 2011 1 hv 2 Mc hv 3 h v 4 Zero

wer Q 11 Q 12 and Q 13 by appropriately matching the information given in the three columns of the following table Q 11 Q 12 13 Work functions of four metals are given below Metals Where Na Zn Cu Pt Consider the Einstien equation for photoelectric effect eVo hv p Vo stopping potential hv energy of radiation photon work function of metal Now consider the following three column Culumn 1 Metal Pt combination A 1 ii R C II ii P Column 2 Wave length of radiation 283 nm Work function 2 38 eV 4 35 eV 4 70 eV 6 40 eV 1 II Cu III Zn IV Na Which of the following options is correct i ii 192 nm iii 262 nm iv 518 nm B I ii P D II ii Q Which of the following options is correct combination A IV iii S C III iii S B IV iv S D III i S Which of the following options is correct combination A II iv P B III i R Column 3 Stopping potential P 0 Q 0 35 eV R 1 7 eV S 1 32 eV

5 A source of power 600 kW emits photon which incident on a surface 2 5 m away out of which 50 is reflected back what is the radiation pressure on the surface 1 3 9 x 105 Pa 2 7 8 x 10 5 Pa 3 11 7 x 10 5 Pa 4 15 6 x 10 5 Pa

A beam of light has three wavelengths 4144 4972 6216 with a total intensity 3 6x10 W m equally distributed amongst the three wavelengths The beam falls normally on a area 1 0 cm of a clean metallic surface of work function 2 3 eV Assume that there is no loss of ligh by reflection and that each energetically capable photon ejects one electron Calculate the number c photoelectrons liberated in two seconds In a photo electric effect set up a point source of light of power 3 2 x 10 W emits mono energeti Foneca 5 0 cV The source is located at a distance of 0 8 m from the centre of a stationary

18 36 54 In photoelectric effect experiment the frequency of incident light is three times of threshold frequency and saturation curren is i Now wavelength of light is made four times of initial wavelength and intensity is doubled the new saturation curren will be on 21 2 14 3 3i fan 1 1 2 The m 4 Zero of their de Broglie wavelength is

An electron and a proton are separated by a large distance and the electron approaches the proton with a kinetic energy of 4 11 eV If the electron is captured by the proton to form hydrogen atom in the ground state the wavelength of photon given off is a x 10 Fill the value of a in your OMR

In a common emitter CE amplifier having a voltage gain G the transistor used has transconductance 0 03 mho and current gain 25 If the above transistor is replaced with another one with transconductance 0 02 mho and current gain 20 the voltage gain will be 1 G 2 2 3 G

6 18 The magnetic field associated with a light wave is given at the origin by B B sin 3 14 107 ct sin 6 28 10 ct If this light falls on a silver plate having a work function of 4 7 eV what will be the maximum kinetic energy of the photo electrons c 3 108 ms h 6 6 10 34J s 1 JEE 2018 a 7 72eV b 8 52 eV c 12 5eV d 6 82 eV

3 An electron in the hydrogen atom jumps from excited state n to the ground state The wavelength so emitted illuminates a photosensitive material having work function 2 75 eV If the stopping potential of the photoelectron is 10 V then the value of n is 1 5 3 3 2 2 4 4

Figure shows the variation of photoele i with anode potential V for a photosensitive surface for two radiations of intensities I and I and frequencies va and vo for the curves a and b Vb respectively It follows from the graph that Vo 1 va Vb b la b a F V O 2 va Vb lb l a A

OTwo blocks are hanging by massless strings beam of light is allowed to fall as shown in figure Assuming that lower surface of lower block is perfectly reflecting and light incident normal to the surface Energy falling on lower block is w every second Find tension in upper string AB Assume no light energy falls on upper block 1 mig m g 1 A B C D 3 2w m 111 2w C m light 2 m g m g W W C

1 potential versus Wavelength and reciprocal of slope of graph will be hc Straight line e 2 Rectangular hyperbola 3 Straight line graph of stopping is drawn Nature C e hc

An amplifier has a voltage gain A 1000 The voltage gain in dB is 1 30 dB 3 3 dB 2 60 dB 4 20 dB

Answer Q 11 Q 12 and Q 13 by appropriately matching the information given in the three columns of the following table 11 12 Work functions of four metals are given below Metals Where Na Zn Cu Pt Consider the Einstien equation for photoelectric effect eVo hv p combination A 1 ii R C II ii P Vo stopping potential hv energy of radiation photon work function of metal Now consider the following three column Culumn 1 Metal 1 Pt II Cu III Zn IV Na Which of the following options is correct 1 Work function 6 2 38 eV 4 35 eV 4 70 eV 6 40 eV Column 2 Wave length of radiation 283 nm ii 192 nm iii 262 nm iv 518 nm B I ii P D II ii Q Which of the following options is correct combination A IV iii S C ii S B IV iv S D III i S Column 3 Stopping potential P 0 Q 0 35 eV R 1 7 eV S 1 32 eV