Radioactivity Questions and Answers

18 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

D 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

The 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

Two 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

A 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

Consider 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

When 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

7 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

Which 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

09 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

4 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

The 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

The 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

4 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

Two 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

The 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

A 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

1 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

At 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

21 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

The 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

Tritium 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

A 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

2 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

Starting 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

We 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

Question 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

In 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

15 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

EXERCISE 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

If 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

The 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

Two 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

If 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

The 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

Like 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

Nuclei 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

A 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

5 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

Which 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

2 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

Calculate 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

There 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

The 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

A 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

39 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

8 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

Q 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

Two 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

7 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