(c) Heat lost by ice = Heat gained by water + Heat gained by copper

Question 10:

(a) (i) State two properties which a substance should possess when used as a thermionic emitter.
(ii) When an alpha particle gains two electrons it becomes neutral and becomes an atom of an element which is a rare gas. What is the name of this rare gas ?  [3]

(b) (i) Define radioactivity.
(ii) What happens inside the nucleus that causes the emission of beta particle ?
(iii) Express the above change in the form of an equation.  [3]

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(c) (i) Name a device which is commonly used to convert an electrical signal into a visual signal.
(ii) The nucleus $_{ 84 }^{ 202 }{ X }$ emits an alpha particle and forms the nucleus Y. Represent this change in the form of an equation.
(iii) What changes will take place in the mass number and atomic number of the nucleus Y if it emits gamma radiations ?  [4]

Answer:10

(a) (i) 1. Low Work Function
2. High Melting Point.
(ii) Helium gas.

(b) (i) Radioactivity is a random nuclear phenomenon in which spontaneous emission of α β or γ radiations from the nuclei of atoms during their decay takes place.
(ii) In an unstable nucleus, number of neutrons are more than number of protons. In such a case, a neutron may change to a proton to achieve stability by emitting an electron called beta particle.
(iii)

(c) (i) Cathode Ray Tube.
(ii)

(iii) No change.

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