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1 TEST-7 TOPIC: ELECTRONIC DEICES ND DUL NTURE OF MTTER Q.1 Lights of two different frequencies whose photons have energies 1e and.5 e respectively, successively illuinate a etal of work function.5 e. The ratio of axiu speeds of the eitted electrons will be () 1 : 5 () 1 : 4 1 : 1 : 1 Q. If stopping potentials corresponding to wavelengths 4 Å and 45 Å are 1.3 and.9 respectively, then the work function of the etal is ().3 e.3 e () 1.3 e 5 e. Q.3 Photoelectric effect support quantu nature of light because () there is iniu frequency of light below which no photoelectrons are eitted () the axiu kinetic energy of photoelectrons depends only on the frequency of light and not on its intensity even when the etal surface is faintly illuinated, the photoelectrons leave the surface iediately. ll of the above Q.4 Which of the following phenoena can be explained only on the basis of quantu theory of light? () Energy spectru of black body radiation () toic spectra Photoelectric effect ll of the above Q.5 Light of wavelength strikes a photoelectric surface and electrons are ejected with kinetic energy K. If K is to be increased to exactly twice its original value, the wavelength ust be changed to ' such that () ' < > ' > () ' > ' = Q.6 If in a photoelectric experient, the wavelength of incident radiation is reduced fro 6 Å to 4 Å, then () stopping potential will decrease () stopping potential will increase kinetic energy of eitted electrons will decrease the value of work function will decrease Q. 7 The frequency of incident light falling on a photosensitive etal plate is doubled, the KE of the eitted photoelectrons is () double the earlier value () unchanged ore than doubled less than doubled Q.8 When light of intensity I 1 and frequency 1 is incident on a substance, photoelectric eission take place and variation potential () is as shown by curve (1) in the figure. However, if light of intensity I and frequency falls on the sae substance, photoelectric current varies with potential as shown by curve () which of the following is correct - Current (1) () Potential () I 1 = I, 1 = () I 1 > I, 1 > I 1 > I, 1 < I 1 < I, 1 < Q.9 The work functions for etals, and C are respectively 1.9 e,. e and 5 e. ccording to Einstein's equation, the etals which will eit photo-electrons for a radiation of wavelength 41 Å is/are - () None and only () only ll the three etals Q.1 photocell is illuinated by a sall bright source placed 1 away. When the sae source of light is placed 1/ away, the nuber of electrons eitted by photocathode would - Page 1 of 6

2 () increase by a factor of () decrease by a factor of increase by a factor of 4 decrease by a factor of 4 Q.11 In a photoelectric experient, electrons are ejected fro etals and by light of frequency ƒ. The potential difference required to stop the electrons is easured for various frequencies. If has a greater work function than, which graph illustrates the expected results? () () ƒ ƒ ƒ ƒ Q.11 In a photoelectric cell, the wavelength of incident light is changed fro 4 Å to 36 Å. The change in stopping potential will be - ().14 () Q.1 The work function for aluiniu is 4.15 e. The cut-off wavelength for photoelectric effect for aluiniu is - () 3 n () n 4 n 15 n Q.13 The stopping potential ( ) versus frequency () plot of a substance is shown in figure, the threshold wavelength is Hz () () 6Å 5Å Can not be estiated fro given data Q.14 Figure represents a graph of kinetic energy (K) of photoelectrons (in e) and frequency () for a etal used as cathode in photoelectric experient. The work function of etal is K () 1 e () 1.5 e e 3 e Q.15 Figure represents the graph of photo current I versus applied voltage (). The axiu energy of the eitted photoelectrons is i () e () 4 e e 4 J Q.16 The photoelectric threshold frequency of a etal is. When light of frequency 4 is incident on the etal, the axiu kinetic energy of the eitted photoelectrons is - () 4 h 5 h () 3 h 5h Q.17 The axiu velocity of an electron eitted by light of wavelength incident on the surface of a etal of work function W is - (hc W) () (hc W) () (hc W) (h W) Q.18 The figure shows the variation of photo current with anode potential for a photo-sensitive surface for three difference radiations. Let I a, I b, and I c be the intensities and f a, f b and f c be the frequencies for the curves a,b and c respectively - Page of 6

3 c b () f a = f b and I a I b () f a = f c and I a = I c f a = f b and I a = I b Photo current a O node potential f b = f c and I b = I c Q.19 In a photo eissive cell with executing wavelength, the fastest electron has speed v. If the exciting wavelength is changed to 3/4, the speed of the fastest eitted electron will be - () v (3/4) 1/ () v (4/3) 1/ Less than v (4/3) 1/ Greater than v (4/3) 1/ Q. Two identical photocathode receive light of frequencies f 1 and f. If the velocities of the photo electrons (of ass ) coing out are respectively v 1 and v, then h f 1 f () v 1 v = 1 v () v h = (f 1 f ) h f 1 f v 1 v = 1 v v h = (f 1 f ) 54 n n Q.3 The forward biased diode is - () () Q.4 Which logic gate is represented by the following cobination of logic gates? () OR () NND ND NOR Q.5 Input wavefors and as shown in Fig-I are applied to the cobination of gates as shown in Fig-II. Which of the wavefors shown in Fig. (i) to (iv) correctly represents the output wavefor? Fig-(i) Fig-I Fig-II Q.1 radiation of energy E falls norally on a perfectly reflecting surface. The oentu transferred to the surface is () E/c () E/c E/c E/c Fig-(ii) Fig-(iii) Q. The work function of a substance is 4. e. The longest wavelength of light that can cause photoelectron eission fro this substance is approxiately - () 31 n () 4 n () Fig.(i) Fig.(iii) Fig-(iv) () Fig.(ii) Fig. (iv) Page 3 of 6

4 Q.6 For a transistor, =.9, the value of is - () 1 () Q.7 In the circuit shown in figure the axiu output voltage is i 1 T/ T t r r Q.31 zener diode is to be used as a voltage regulator. Identify the correct set up D 1 k D k k () 5 () () 5 1 Q.8 The following configuration of gate is equivalent to- OR NND ND G 3 () () NND OR Q.9 Find G () OR None of these () 1 () 3 None of these Q.3 Which one is showing the characteristics of a zener diode? Q.3 If a seiconductor has an intrinsic carrier concentration of , when doped with phosphorus, then the concentration of holes at roo teperature will be () 1 1 () r r Q.33 n p-n junction shown in the figure can act () () as a rectifier. n alternating current source () is connected in the circuit. Page 4 of 6

5 The current (I) in the resistor R can be shown by () () Q.34 What is out put of the gate circuit shown in figure? (). ()... Q.35 The logic circuit shown below has the input wavefors and as shown. Pick out the correct output wavefor. Q.36 n n p n transistor circuit has =.985. If I c =, then value of I b is - ().3 () Q.37 If input in a full-wave rectifier is e = 5 sin 314t volt, diode resistance is 1 and load resistance is 1K then. (1) Pulse frequency output voltage is 1. () Input power is 1136 w (3) Output power is 87 w (4) Efficiency is 81. % () 1, 3 () 1, 1,, 3 1,,3,4 Q.38 n n-p-n transistor circuit is arranged as shown, it is a N P N R = 1 K Output is : () Coon base aplifier circuit () Coon-eitter aplifier circuit Coon-collector aplifier circuit None Q.39 In N-type seiconductors, the concentration of inority charge carriers ainly depends upon - () the dopping technique () the dopping ratio the teperature of the aterial None Page 5 of 6

6 Q.4 n P-N-P transistor circuit is arranged as shown. It is a P N P = 1 K () coon base aplifier circuit () coon-eitter aplifier circuit coon-collector circuit None Q.41 Following circuit is equivalent to () ND gate () OR gate NOT gate -OR gate Q.4 Current through the ideal diode is () zero () 5 Q.43 If n e and n h are the nuber of electrons and holes in a sei-conductor heavily doped with phosphorus, then - () n e >> n h () n n h n e << n h none Q.44 n n-type sei-conductor is - () negatively charged () positively charged neutral negatively or positively charged depending upon the aount of ipurity Q.45 In p-type sei-conductor the ajority charge carriers are - () electrons () holes neutrons protons Page 6 of 6

22 - ELECTRON AND PHOTONS Page 1 ( Answers at the end of all questions )

22 - ELECTRON AND PHOTONS Page 1 1 ) A photocell is illuinated by a sall source placed 1 away. When the sae source of light is placed 1 / 2 away, the nuber of electrons eitted by photocathode would ( a