Physics M.C.Q (1 Marks)

At any instant the ratio of the amount of radioactive substances is 2 : 1. If their half lives be respectively 12 and 16 hours, then after two days, what will be the ratio of the substances

(a) 1 : 1

(b) 2 : 1

(c) 1 : 2

(d) 1 : 4

An element A decays into element C by a two step process :

A → B +  

B → C +  

Then

(a) A and C are isotopes	(b) A and C are isobars
(c) A and B are isotopes	(d) A and B are isobars

A radioactive sample with a half life of 1 month has the label : “Activity=2 micro curies on 1.8.1991.'' What will be its activity two months later

(a) 1.0 micro curies

(b) 0.5 micro curies

(c) 4 micro curies

(d) 8 micro curies

The nucleus   after two successive   decays will give

(a)

(b)

(c)

(d)

In the given nuclear reaction A, B, C, D, E represents     

(a) A = 234, B = 90, C = 234, D = 91, E = β

(b) A = 234, B = 90, C = 238, D = 94, E = α

(c) A = 238, B = 93, C = 234, D = 91, E = β

(d) A = 234, B = 90, C = 234, D = 93, E = α

Half life of a radioactive element is 10 days. The time during which quantity remains 1/10 of initial mass will be

(a) 100 days

(b) 50 days

(c) 33 days

(d) 16 days

The particles emitted by radioactive decay are deflected by magnetic field. The particles will be

(a) Protons and α - particles	(b) Electrons, protons and α -particles
(c) Electrons, protons and neutrons	(d) Electrons and α -particles

Which of the following statements are true regarding radioactivity

(I)  All radioactive elements decay exponentially with time

(II)  Half life time of a radioactive element is time required for one half of the radioactive atoms to disintegrate

(III)  Age of earth can be determined with the help of radioactive dating

(IV)  Half life time of a radioactive element is 50% of its average life period

Select correct answer using the codes given below

Codes :

(a) I and II

(b) I, III and IV

(c) I, II and III

(d) II and III

An atom of mass number 15 and atomic number 7 captures an α - particle and then emits a proton. The mass number and atomic number of the resulting product will respectively be

(a) 14 and 2

(b) 15 and 3

(c) 16 and 4

(d) 18 and 8

Carbon -14 decays with half-life of about 5,800 years. In a sample of bone, the ratio of carbon -14 to carbon -12 is found to be   of what it is in free air. This bone may belong to a period about x centuries ago, where x is nearest to

(a) 2 × 58

(b) 58

(c) 58/2

(d) 3 × 58

The half life of  is 8 days. Given a sample of  at time t = 0, we can assert that

(a) No nucleus will decay before t = 4 days

(b) No nucleus will decay before t = 8 days

(c) All nuclei will decay before t = 16 days

(d) A given nucleus may decay at any time after t = 0

If the radioactive decay constant of radium is 1.07  per year, then its half life period is approximately equal to

(a) 8,900 years

(b) 7,000 years

(c) 6,476 years

(d) 2,520 years

A nucleus  emits one α  and one β  particles. The resulting nucleus is

(a)

(b)

(c)

(d)

Half lives of two radioactive substances A and B are respectively 20 minutes and 40 minutes. Initially the sample of A and B have equal number of nuclei. After 80 minutes, the ratio of remaining number of A and B nuclei is

(a) 1 : 16

(b) 4 : 1

(c) 1 : 4

(d) 1 : 1

Which of the following is a correct statement

(a) Beta rays are same as cathode rays

(b) Gamma rays are high energy neutrons

(c) Alpha particles are singly ionized helium atoms

(d) Protons and neutrons have exactly the same mass

Binding energy per nucleon verses mass number curve for nuclei is shown in the figure. W, X, Y and Z are four nuclei indicated on the curve. The process that would release energy is

(a) Y →  2Z

(b) W → X + Z

(c) W → 2Y

(d) X → Y + Z

Which of the following isotopes is used for the treatment of cancer

(a)

(b)

(c)

(d)

After 1α and 2β emissions

(a) Mass number reduces by 3	(b) Mass number reduces by 4
(c) Mass number reduces by 6	(d) Atomic number remains unchanged

In the uranium radioactive series, the initial nucleus is  and the final nucleus is  . When the uranium nucleus decays to lead, the number of α - particles emitted will be

(a) 1

(b) 2

(c) 4

(d) 8

Half life of a radioactive substance is T.  The time taken for all the nuclei to disintegrate will be

(a) 2T

(b) T2

(c) 4T

(d) Uncertain

The half life period of a radioactive substance is 5 min. The amount of substance decayed in 20 min will be

(a) 93.75%

(b) 75%

(c) 25%

(d) 6.25%

The half life (T) and the disintegration constant (λ) of a radioactive substance are related as

(a) λT  = 1

(b) λT = 0.693

(c)

(d)

The rate of disintegration of fixed quantity of a radioactive element can be increased by

(a) Increasing the temperature	(b) Increasing the pressure
(c) Chemical reaction	(d) It is not possible

In a radioactive decay, neither the atomic number nor the mass number changes. Which of the following would be emitted in the decay process

(a) Proton

(b) Neutron

(c) Electron

(d) Photon

The radioactive decay of uranium into thorium is expressed by the equation  where ‘X’ is

(a) An electron

(b) A proton

(c) A deuteron

(d) An alpha particle

The counting rate observed from a radioactive source at t = 0 second was 1600 counts per second and at t = 8 seconds it was 100 counts per second. The counting rate observed, as counts per second at t = 6 seconds, will be

(a) 400

(b) 300

(c) 200

(d) 150

A radioactive nucleus  decays to  . Which of the following particles are emitted

(a) One alpha and one electron	(b) Two deuterons and one positron
(c) One alpha and one proton	(d) One proton and four neutrons

A element used for radioactive carbon dating for more than 5600 years is

(a) C - 14

(b) U - 234

(c) U - 238

(d) Po - 94

A radioactive substance has a half life of 60 minutes. After 3 hours, the fraction of atom that have decayed would be

(a)12.5%

(b) 87.5%

(c) 8.5%

(d) 25.1%

A radioactive reaction is  → . How many α and β particles are emitted

(a) 10α, 6β	(b) 4 protons, 8 neutrons
(c) 6 electrons, 8 protons	(d) 6β, 8α

What is the respective number of α and β  particles emitted in the following radioactive decay

(a) 6 and 8

(b) 8 and 8

(c) 6 and 6

(d) 8 and 6

The count rate of a Geiger- Muller counter for the radiation of a radioactive material of half life of 30 minutes decreases to 5 after 2 hours. The initial count rate was

(a) 25

(b) 80

(c) 625

(d) 20

Unit of radioactivity is Rutherford. Its value is

(a) 3.7  disi tegrations/sec	(b) 3.7  disintegrations/sec
(c) 1.0  disintegrations/sec	(d) 1.0  disintegrations/sec

The binding energy of deuteron  is 1.112 MeV per nucleon and an α - particle  has a binding energy of 7.047 MeV per nucleon. Then in the fusion reaction  the energy Q released is

(a) 1 MeV

(b) 11.9 MeV

(c) 23.8 MeV

(d) 931 MeV

If 20 gm of a radioactive substance due to radioactive decay reduces to 10 gm in  4 minutes, then in what time 80 gm of the same substance will reduce to 10 gm

(a) In 8 minutes

(b) In 12 minutes

(c) In 16 minutes

(d) In 20 minutes

The half life of the isotope  is 15 hrs. How much time does it take for   of a sample of this isotope to decay

(a) 75 hrs

(b) 65 hrs

(c) 55 hrs

(d) 45 hrs

Consider a radioactive material of half-life 1.0 minute. If one of the nuclei decays now, the next one will decay

(a) After 1 minute

(b) After   minute

(c) After  minute, where N is the number of nuclei present at that moment

(d) After any time

The correct order of ionizing capacity of α, β and γ - rays is

(a) α >  γ > β

(b) α > β > γ

(c) α < β <γ

(d) α > β > γ

The half life of polonium is 140 days. After how many days, 16 gm polonium will be reduced to 1 gm  (or 15g will decay)

(a) 700 days

(b) 280 days

(c) 560 days

(d) 420 days

Which can pass through 20 cm thickness of the steel

(a) α -  particles

(b) β - particles

(c) γ-  rays

(d) Ultraviolet rays

Three α - particles and one β - particle decaying takes place in series from an isotope . Finally the isotope obtained will be

(a)

(b)

(c)

(d)

Some radioactive nucleus may emit

(a) Only one α,β or γ at a time

(b) All the three α,β  and  γ one after another

(c) All the three α,β  and γ  simultaneously

(d) Only α and β  simultaneously

A radioactive element emits 200 particles per second. After three hours 25 particles per second are emitted. The half life period of element will be

(a) 50 minutes

(b) 60 minutes

(c) 70 minutes

(d) 80 minutes

Curie is a unit of

(a) Length

(b) It is not any unit

(c) Activity

(d) Atomic number

A radio-isotope has a half- life of 5 years. The fraction of the atoms of this material that would decay in 15 years will be

(a) 1/8

(b) 2/3

(c) 7/8

(d) 5/8

The relationship between λ and half life ( of a radioactive substance is

(a) λ =

(b)  λ =

(c) λ =

(d)  λ =

A sample contains 16 gm of a radioactive material, the half life of which is two days. After 32 days, the amount of radioactive material left in the sample is

(a) Less than 1 mg

(b)

(c)

(d) 1 gm

The decay constant of a radioactive element is 0.01 per second. Its half life period is

(a) 693 sec

(b) 6.93 sec

(c) 0.693 sec

(d) 69.3 sec

Atomic mass number of an element thorium is 232 and its atomic number is 90. The end product of this radioactive element is an isotope of lead (atomic mass 208 and atomic number 82). The number of alpha and beta particles emitted is

(a) α = 3, β = 3

(b) α = 6, β = 4

(c) α = 6, β = 0

(d) α = 4, β = 6

16 gm sample of a radioactive element is taken from Bombay to Delhi in 2 hour and it was found that 1 gm of the element remained (undisintegrated). Half life of the element is

(a) 2 hour

(b) 1 hour

(c)

(d)