# Radioactivity Questions and Answers

Physics

Radioactivity18 Shift 1 An active nucleus decays to one third 13 in 20 Hrs The fraction of original activity re maining after 80 Hrs is 1 a b 16 1 c d 36 1 812201 1 54

Physics

RadioactivityD A certain radioactive element has a half life of 20 years If we have a block with 10 g of the element in it after how many years will there be just 2 5 g of the element in the block a 80 years 40 years c 100 years 60 years b d 1995 2001

Physics

RadioactivityThe plane wall of an oven is of thickness L 0 05 m and is exposed to the surrounding at 300 K The outer surface of the oven exposed to the surrounding is at temperature 320 K in steady state The energy radiated in W m by outer surface is proportional to the temperature difference between the surface and the surrounding with proportionality constant 20 W m K What is the temperature of inner surface of the oven in steady state if the wall has a thermal conductivity of K 0 5 W m K A 400 K C 380 K B 340 K D 360 K

Physics

RadioactivityTwo radioactive sources A and B of half lives of 1 hour an 2 hours respectively initially contain the same number of radioactive atoms At the end of two hours their rates of disintegration are in the ratio of to

Physics

RadioactivityA nuclear fusion reaction is given below H H He n 3 2 MeV A How much energy will be generated when 2 kg of deuterons are fused approx 1 1030 eV D 2 5 x 1023 MeV 2 1022 Mo 4 1033 eV

Physics

RadioactivityConsider the following reaction HHHH Yer The atomic masses are given as m H 1 007825 u m H 2 014102 u m H 3 016049 u 4 0 linn ofteaq The Q value of the above reaction will be 1 4 03 MeV OP 2 2 01 MeV 3 2 01 MeV 4 4 03 MeV

Physics

RadioactivityWhen Th238 changes into Bi222 then the number 90 of emitted a and B particles are 2 4a 7B 4 4a 18 1 8a 7B 3 4a 4p men 5 svig toolqmsa 83 16 107

Physics

Radioactivity7 If E is the amount of energy released radioactive element having mass number A undergoes alpha decay then the velocity of alpha particle is 1 3 2Q VA 4 A 4 E 2 4 2 A 4 E V Ama 2AE

Physics

RadioactivityWhich of the following statement is true A catalyst alter Gibbs energy of a reaction The action of the catalyst cannot be explaine by intermediate complex theory O A catalyst does not change the equilibrium constant of a reaction O Catalyst catalyses the non spontaneous reaction

Physics

Radioactivity09 There are two radio nuclie A and B A is an alpha emitter and B is a beta emitter Their distintegration constants are in the ratio of 1 2 What should be the ratio of number of atoms of two at time t 0 so that probabilities of getting a and particles are same at time t 0 A 2 1 C e B 1 2 D e

Physics

Radioactivity4 If the energy released in the fission of one nucleus is 200MeV Then the number of nuclei required per second in a power plant of 16KW will be A 0 5 x 1014 C 5 x 1012 B 0 5 x 1012 D 5 x 1014

Physics

RadioactivityThe ratio of masses of two copper spheres of identical surfaces is 8 1 If their temperatures are 2000K and 1000 respectively then the ratio of energies radiated per second by the two is 1 128 1 2 64 1 3 16 1 4 4 1 mom terial and radius with height equal to the radi

Physics

RadioactivityThe rate of emission of energy by a unit area of a body is 10 watt and that of sun is 10 watt The emissive power the body is 0 1 If the temperature of the sun is 6000K then the temperature of the body will be 4 600 10 K 1 6000K 2 600K 3 600 10 K

Physics

Radioactivity4 If Assertion Reason both are false The temperature of a body is increased from 73 C to 327 C Then the ratio of emissive power is AIIMS 2 3 27 4 81 1 1 9 2 1 27 A body initially at 80 C cools to 64 C in 5 min and to 52 C in 10 min The temperature of the surrounding is

Physics

RadioactivityTwo particles Y and Z emitted by a radioactive source at P made tracks in a cold chamber as illustrated in the figure A magnetic field acted downward into the paper Carful measurements showed that both tracks were circular the radius of Y track being half that of the Z track Which one of the following statements is certainlty true fi za f fuff P af fagur tefter for any f A Both Y and Z particles carried a positive charge ciaria B The mass of Z particle was one half that of the Y particle C The mass of the Z particle was twice that of the Y particle I D The charge of the Z particle was twice that of the Y particle Your Answer

Physics

RadioactivityThe mass of radium mass number 226 half life 1600 years with an activity of one curie is almost 544 2261600 A B OU O 1 gram 1 8 gram C 2 gram D 3 2 gram Your Answer

Physics

RadioactivityA radioactive isotope A with a half life of 1 25 x 1010 year decays into B wh stable A sample of rock from a planet is found to contain both A and B pre in the ratio 1 15 The age of the rock is 0 4x107 year O 5 x 10 year O 5 10 0 year O 4 x 10 1 year

Physics

Radioactivity1 2 1 2 3 2 3 4 2 In a sample of radioactive material what percentage of the initial number of active nuclei will during one mean life 1 63 2 50 3 77 4 88 2 RPMT 2014 The angle voluate of photocell is kept fixed The wavelength 2 of the light falling o the cathode is gradually changed RPMT 2014 KF of the photoelectrons emitted varies with as

Physics

RadioactivityAt a given instant there are 25 undecayed radioactive nuclei in a sample After 10 sec the number of undecayed nuclei reduces to 6 25 the mean life of the nuclei is Question Type Single Correct Type 1 14 43 sec 2 7 21 sec 3 5 sec

Physics

Radioactivity21 A particle of charge q is moving with velocity v in the presence of crossed electric field E and magnetic field B as shown in the figure i Write an expression for the force experienced by the charge and under what condition will the particle to move along the x axis ii How the trajectory of the particle would be affected if the electric field is switched off and the velocity has a component along B Draw it FE E V

Physics

RadioactivityThe half life of a radioactive isotope X is 25 years It decays to another element Y which is stable The two elements X and Y were found to be in the ratio of 1 15 in a sample of a given rock The age of the rock was estimated to be Question Type Single Correct Type 1 150 years 2 200 years 3 250 years 4 100 years

Physics

RadioactivityTritium t 2 12 33 y is mostly produced for military purposes If we had stopped producing tritium in 1960 with a 2500 kg stockpile how much would be left in the year 2015 Enter your answer in kg ka

Physics

RadioactivityA y ray photon produces an electron positron pair If the rest mass energy of electron is 0 51 Mev and the total kinetic energy of electron positron pair is 0 78 MeV then the energy of Y ray photon in Mey is 1 0 78 2 1 8 3 1 28 4 0 28

Physics

Radioactivity2 A nuclear transformation is denoted by X n a Li Which of the following is the nucleus of element X a Be 10 d B inquit onerating from 50 Hz mains b 2C6 c Be

Physics

RadioactivityStarting with a sample of pure 66 Cu c 7 minutes 8 Zn in 15 minutes The corresponding half life is a 15 minutes b 10 minutes of it decays into d 5 minutes

Physics

RadioactivityWe are given the following atomic masses 238 238 05079 u16 234Th 234 04363 u 2013 4He 4 00260 u gitvilos brit boow The energy released during the alpha decay of 238 U is 1 6 00 MeV 3 3 75 MeV 2 4 25 MeV 4 5 03 MeV

Physics

RadioactivityQuestion 35 A Activity of a radioactive nuclei 100x sample is 6 023 1012 dps then mass of radioactive nucleii sample will be given 2 of X is 10 min B C 10 10 gm M M 4 00 6 10 10 gm 10 11gm N M 1 00 Correct Answer

Physics

RadioactivityIn the presence of an inhomogeneous weak magnetic field spectral fines due to transitions between two set of states were observed 1 H and 2 DS 2 P3 2 512 The types of Zeeman effect observed in 1 and 2 respectively are a normal normal c anomalous normal The number of levels into which each of the above four terms split into respectively is a 6 4 10 8 b 4 6 10 12 c 11 9 6 4 d 9 5 12 10 ME b anomalous anomalous d normal anomalous

Physics

Radioactivity15 Find the focal length of a plano convex lens when curved surface is silvered and the object is in front of plane surface A f behaves as concave mirror behaves as concave lens C R B D f behaves as convex mirror behaves as convex lens R 24

Physics

RadioactivityEXERCISE 13 2 Half life of a radioactive element is 40 minute What amount will remain undecayed after 4 hour 1 1 32 3 1 128 1 2 64 4 1 16 lives and to respectively W

Physics

RadioactivityIf sun radiates electromagnetic energy of 18 3 9 x 1026 watt and radius of sun is 6 96 x 108 m then intensity of sunlight at the solar surface will be 1 5 6 x 106 W m 3 4 2 x 106 W m 2 6 4 x 107 W m 4 4 2 x 10 W m

Physics

RadioactivityThe energy gap of an element is given as 5 9 10 ev Calculate the intrinsic com length if 1 5 82 10 m s n 5 0 mm b 1 2 m c 9 5 mm d 2 1 m Answer 8 question 3 e ec D

Physics

RadioactivityTwo radioactive substances A and B have decay constants 4 and respectively At t 0 they have the same number of nuclei The ratio of number of nuclei of A to those of B will be after a time interval of 1 2 2 3 a

Physics

RadioactivityIf the nucleus 4X has a radius of about 3 6 fm then 125 would have the radius as A 27 3 6 fm 6 0 fm 4 8 fm 7 2 fm A Y

Physics

RadioactivityThe activity of a sample is measured as No counts per minute at t 0 and No e counts at t 10 minutes The time in minutes at which the activity reduces to half its value is 5log 0 2 5log 2

Physics

RadioactivityLike an atom when a nucleus is in excited state spontaneously decays to its ground state and a photon is emitted with energy of order of eV keV meV

Physics

RadioactivityNuclei of radioactive element A are produced at rate 2 where t is time at any time t The element A has decay constant A Let N be the number of nuclei of element A at any time t F time t to dN dt is minimum The number of nuclei of element A at time t to is ONO Xt 12 2to At to

Physics

RadioactivityA radioactive isotopes is being produced at a constant rate X Half life of substance is Y After some time the no of radioactive nuclei become constant The value of constant is ONO XY in 2 XY In 2 XY

Physics

Radioactivity5 A radioactive isotope a has half life of 2 3 105 yrs The isotope decays into stable 3 A rock sample discovered by archaeologist contains a as 1 15 What could be the possible age of the rock a 9 2 105 yrs b 4 6 105 yrs c 6 9 105 yrs d 1 38 106 yrs O A O B O C C

Physics

RadioactivityWhich of the following statements is false A C D The energy spectrum of a decay is line spectrum The energy spectrum of B particles is continuous The energy spectrum of y decay is continuous The energy spectra of a y decay are line spectra

Physics

Radioactivity2 A photon of energy E ejects a photo electron from a metal surface whose work function is Po The electron then enters into an uniform magnetic field B in a direction perpendicular to the field It is observed that the electron describes a circular path Then calculate the radius r of the path a b c d eB O O O O A B 2M E Po eB 2M E Po eB O C D 2M Po E eB 2M o E

Physics

RadioactivityCalculate the energy generated in MeV when 0 1 kg of Li is converted to He by proton bombardmen Given masses of Li He and H in a m u are 7 0183 4 0040 and 1 0081 respectively Li H 2 He Q

Physics

RadioactivityThere is a stream of radioactive material having No number of nuclei initially moving with constant speed of 2500 m s If half life of material is 693 s then amount of material remain after they travel a NCERT Pg 448 distance of 2500 km is 1 No 2 4 3 No 2 LARA Dettol 2 G 4 No 2 e No 4

Physics

RadioactivityThe nuclear binding energy may be approximated by the empirical expression B E q A a A 3 a 2 A a4 A 2Z A Considering a set of isobaric nuclei derive a relationship between A and Z for naturally occuring nuclei A a 2 A a3 az A213 2a b A az A213 2a c A a4 A2 3 293 2 d 2 94 41 13 203

Physics

RadioactivityA radioactive element X converes into another stable element Y Half life of X is 2hrs Initially only X is present After time t the ratio of atoms of X and Y is found to be 1 4 then t in hours is x 2 3 between 4 and 6 2 4 4 6

Physics

Radioactivity39 Half lives of two radioactive nuclei A and B are 10 minutes and 20 minutes respectively If initially a sample has equal number of nuclei then after 60 minutes the ratio of decayed numbers of nuclei A and B will be 1 3 8 2 1 8 3 8 1 A 0 0

Physics

Radioactivity8 Half life of a radioactive substance is 2 34 minute It is produced at a constant rate of 10 nuclei per sec How soon after in minute the beginning of production will its activity be equal to 7 5 10 disintegration per sec

Physics

RadioactivityQ Nos 10 11 are based on the following paragraph A nucleus of mass M Am is at rest and decays into two daughter nuclei of equal mass M each 2 Speed of light is c 10 The binding energy per nucleon for the parent nucleus is E and that for the daughter nuclei is Then a E 2E c E E b E E d E 2F

Physics

RadioactivityTwo radio active substances A and B have decay constant 52 and respectively At t 0 they have the same number of active nuclei The ratio of number of active nuclei of A to those of B will be 1 e2 after a time interval O 4 O 22 O 122 Marks 4 1

Physics

Radioactivity7 Consider a radioactive substance which decays following the law of disintegration At an instant t its activity is R and at time t it becomes Find 1 R the average life of radioactive substance if t t in R 1 2 2ln R t 2 t In R 3 t 2 t 1 2ln R 4