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Q.2 Write short answers to any SIX (6) questions.
(i) What are the main postulates of Dalton's Atomic Theory?
Ans Dalton's Atomic Theory:
According to Dalton:
(1) An atom is an indivisible, hard, dense sphere
(2) Atoms of the same element are alike.
(3) Atoms combine in different ways to form a compound.
(ii) Write two/four characteristics of cathode rays.
Ans. Characteristics of Cathode Rays: The cathode rays were studied in detail and their properties were determined, which are given below:
(1) These rays travel in a straight line perpendicular to the cathode surface.
(2) They can cast a sharp shadow of an opaque object if placed in their path
(3)They are deflected towards positive plate in an electric field showing that they are negatively charged.
(4) They raise temperature of the body on which they fall.
(5) J.J. Thomson discovered the charge/mass (e/m) ratio.
(6) Light is produced when these rays hit the sides of the discharge tube.
(7) It was found that the same type of rays were emitted no matter which gas and which anode was used in the discharge tube.
(iii) Write down two/four properties of canal rays.
Ans. The properties of canal rays are as follow:
(1) These rays travel in a straight line in a direction opposite to cathode rays.
(2)Their deflection in electric and magnetic field proved that these were positively charged.
(3) The nature of canal rays depends upon the nature of gas, present in the discharge tube.
(4)These rays do not originate from the anode.
In fact these rays are produced when the cathode rays or electrons collide with residual gas molecules present in the discharge tube and ionize
(5) Mass of these particles was found equal to that of a proton or simple multiple of it.
(v) How the canal rays are produced in the discharge tube?
Ans. These rays do not originate from the anode. In fact these rays are produced when the cathode rays or electrons collide with the residual gas molecule present in the discharge tube and ionize them as follows M+e M 2e
(vi) How it was concluded that cathode rays are fast moving particles called electrons?
Ans. It was observed that when an opaque object is placed in the path of cathode rays, they cast the shadow of the given object. This fact suggested that these are not rays but they are fast moving material particles. Later, they were given the name electrons
(vii) Who discovered an electron, a proton and a neutron?
Ans. In 1897,JJ. Thomson discovered electron.
In 1836, Goldstein discovered positively charged particles called protons
In 1932, James Chadwick discovered a neutron
(viii) Describe the defects of Rutherford's atomic model.
Ans. Defects in Rutherford's Model: Although Rutherford's experiment proved that the plum pudding' model of an atom was not rect, yet it had following defects:
(1) According to classical theory, electrons being the charged particles should release or emit energy continuously and they should ultimately fall into the nucleus.
(2) If the electrons emit energy continuously, they should form a continuous spectrum but in fact, line spectrum was observed
(i) As long as electron remains in an orbit, it does not emit or absorb energy. When it does emit or absorb energy?
Ans. As long as electron remains in a particular orbit it does not radiates or absorbs energy. The energy is emitted or absorbed only when an electron jumps from one orbit to another.
(1) When an electron jumps from lower orbit to higher orbit it absorbs energy.
(2) When it jumps back from higher orbit to lower orbit it radiates energy
(ii) What is classical theory of radiation? How does it differ from quantum theory?
Ans. Classical theory:
According to classical theory of radiation, a hot vibrating body radiates energy all the time it is vibrating.
Quantum theory:
According to quantum theory of radiation, a hot vibrating body does not emit or absorb energy continuously but does so discontinuously in the form of small packets or bundles of energy known as quantum or photons in case of light energy.
(vi) Differentiate between a shell and a subshell with examples.
And. Shells:
"Shells are the main energy levels that electrons occupy while revolving around the nucleus."
Names of Energy Levels:
Energy levels are represented by 'n' values such as 1, 2, 3, .... and so on.
Names of Shells:
When energy levels are called shells, they are designated as K, L, M, N and so on.
Sub-shell:
"A shell consists of a smaller shells called sub-shells or orbitals".
Names (Symbols) of Subshells:
Each subshell or orbital is designated by a small alphabet italic letters such as 's pid and
(vi) Differentiate between radioactive-isotopes dating and radiocarbon dating.
Ans. Radioactive-Isotope Dating: The age determination of very old objects based on the half-lives of the radioactive isotope is called radioactive isotope dating.
Radiocarbon Dating:
The method of age determination of old carbon containing objects (fossils) by measuring the radioactivity o C-14 in them is called radio-carbon dating or simply carbon dating."
(vii) How radio isotopes are used for the treatment of cancer?
Ans. Radio isotopes are used both for skin cancer and organ cancer.
Get A Skin Cancer:
For the treatment of skin cancer, isotopes likep-32 and Sr-90 are used because they emit less penetrating beta radiations.
Organ Cancer: For cancer, Co-60, affecting within the body, is used because it emits strongly penetrating gamma rays.
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