Physics [2 Mark Question Answer]

(a) Alpha radiations have least penetrating power.
(b) Radio isotopes are used in cure of cancer.
(c) Radiations which is omnipresent and can be detected by Geiger Muller tube are called background radiation.

(i) Cathode rays and beta rays have a unit negative charge on each particle. This charge is equal to charge on an electron.
(ii) Cathode rays and beta rays have same mass, as is of one electron.
(iii) Cathode rays and beta rays are deflected by electric and magnetic fields.

(a) When the atomic number of an element exceeds 82 or when the nucleus of an atom has far more number of neutrons as compared to protons, then the nucleus of that atom becomes radioactive.
(b) Radioactivity is not affected by any kind of chemical change.
(c) Slow moving neutrons.

(a) The isotopes of some elements having atomic number less than 82 , such that they emit radioactive radiations are called radio-isotopes.
(b) There will be no change in the nature of radioactivity. Oxidation is the process which takes place in orientation of electrons around the nucleus, whereas radioactivity is associated with protons and neutrons within the nucleus. As no change in nucleus takes place, therefore there is no change in the nature of radioactivity.

(a) The atoms of same element, having the same atomic number but different mass number are called isotopes.
(b) Isotopes are the atoms of same substance (element), which have same atomic number but different mass numbers.
(c) The nucleus of the isotopes have same number of protons but different number of neutrons.

(a) Radioactivity is the phenomenon due to which certain elements give out highly penetrating radiations spontaneously.
(b) The process of combining lighter nuclei (atomic weight less than 20 ) into heavier nuclei with the release of energy, is called nuclear fusion.

(a) Any physical change or chemical change does not alter the rate of decay of the radioactive substance. It means that the phenomenon of radioactivity cannot be due to the orbital electrons which could easily be affected by such changes. So radioactivity is considered to be a nuclear phenomenon.
(b) Atoms of different elements, having the same mass number, but different number of protons (atomic number) are called isobars.

(a) The radiations given out during the decay of radioactive substance can damage living tissues.
(b) Alpha radiations have least penetrating power.
(c) Radio isotopes are used in the cure of cancer under medical supervision.
(d) Radiation which is omnipresent and can be detected by Geiger Muller tube is called background radiation.

(a) The process by which a heavy radioactive nucleus is broken into light nuclei by the bombardment of slow neutrons, so as to liberate energy and more neutrons than used for bombardment is called nuclear fission.
(b) Nuclear chain reaction : This occurs when one single nuclear fission produces more neutrons then absorbed by it, which further disintegrates more nuclei so as to form a chain reaction, with the release of enormous amount of energy in a short span of time is called nuclear chain reaction.

Uncontrolled nuclear fission reaction : As one atom of uranium can liberate three neutrons, and if these neutrons are utilised to break further uranium atoms a kind of chain reaction takes place with spontaneous release of enormous energy. The rate of release of energy during chain reaction is uncontrollable. This principle is used in making atomic bomb.
Controlled nuclear fission reaction : If the fission process is carried out under controlled conditions, ie., the neutrons formed during fission are absorbed by moderators like heavy water or graphite, then the energy so released in the form of heat can be utilised in producing steam, which can be further used in running electric turbines.