Selina Textbook Solutions: Radioactivity | Physics Class 10 ICSE PDF Download

 Page 1


Exercise 12(A) 
Solution 1. 
Three constituent of an atom are: 
1. Electrons: mass is 9.1 x 10
-31 
kg, charge is -1.6 x 10
-19
C 
2. Neutron: mass is 1.6749 x 10
-27
 kg, charge is zero. 
3. Protons: mass is 1.6726 x 10
-27
 kg, charge is +1.6 x 10
-19
 C 
Solution 2. 
Atomic number – the number of protons in the nucleus is called atomic number. 
Mass number – the total number of nucleons in the nucleus is called mass number. 
Solution 3. 
? The nucleus at the centre of atom, whose size is of the order of 10
-15
 m to 10
-14
 m. 
? The size of a nucleus is 10
-5
 to 10
-4
 times the size of an atom. It consists of protons 
and neutrons. 
? If Z is the atomic number and A is the mass number of an atom, then the atom 
contains Z number of electrons; Z number of protons and A – Z number of 
neutrons. 
? The atom is specified by the symbol ZX
A 
where X is the chemical symbol for the 
element. 
Solution 4. 
Atomic number Z = 11 
Mass number A = 23 
Number of neutrons A – Z = 12 
 
Chapter 12 - Radioactivity
Page 2


Exercise 12(A) 
Solution 1. 
Three constituent of an atom are: 
1. Electrons: mass is 9.1 x 10
-31 
kg, charge is -1.6 x 10
-19
C 
2. Neutron: mass is 1.6749 x 10
-27
 kg, charge is zero. 
3. Protons: mass is 1.6726 x 10
-27
 kg, charge is +1.6 x 10
-19
 C 
Solution 2. 
Atomic number – the number of protons in the nucleus is called atomic number. 
Mass number – the total number of nucleons in the nucleus is called mass number. 
Solution 3. 
? The nucleus at the centre of atom, whose size is of the order of 10
-15
 m to 10
-14
 m. 
? The size of a nucleus is 10
-5
 to 10
-4
 times the size of an atom. It consists of protons 
and neutrons. 
? If Z is the atomic number and A is the mass number of an atom, then the atom 
contains Z number of electrons; Z number of protons and A – Z number of 
neutrons. 
? The atom is specified by the symbol ZX
A 
where X is the chemical symbol for the 
element. 
Solution 4. 
Atomic number Z = 11 
Mass number A = 23 
Number of neutrons A – Z = 12 
 
Chapter 12 - Radioactivity
Solution 5. 
Isotopes: the atoms of the same element which have the same atomic number Z but 
differ in their mass number A are called isotopes. 
 
Solution 6. 
Isobars: the atoms of different elements which have the same mass number A, but 
differ in their atomic number Z are called isobars. 
 
Solution 7. 
 
Solution 8. 
Radioactivity: Radioactivity is a nuclear phenomenon. It is the process of spontaneous 
emission of a or ß and ? radiations from the nuclei of atoms during their decay. 
Example: uranium, radium. 
Solution 9. 
There will be no change in the nature of radioactivity. This is because radioactivity is a 
nuclear phenomenon. 
Solution 10. 
(a) Three types of radiations: Alpha, beta and gamma. 
(b) Alpha and beta radiations 
(c) Gamma radiations 
(d) Gamma radiations 
(e) Alpha radiations 
(f) Beta radiations 
Page 3


Exercise 12(A) 
Solution 1. 
Three constituent of an atom are: 
1. Electrons: mass is 9.1 x 10
-31 
kg, charge is -1.6 x 10
-19
C 
2. Neutron: mass is 1.6749 x 10
-27
 kg, charge is zero. 
3. Protons: mass is 1.6726 x 10
-27
 kg, charge is +1.6 x 10
-19
 C 
Solution 2. 
Atomic number – the number of protons in the nucleus is called atomic number. 
Mass number – the total number of nucleons in the nucleus is called mass number. 
Solution 3. 
? The nucleus at the centre of atom, whose size is of the order of 10
-15
 m to 10
-14
 m. 
? The size of a nucleus is 10
-5
 to 10
-4
 times the size of an atom. It consists of protons 
and neutrons. 
? If Z is the atomic number and A is the mass number of an atom, then the atom 
contains Z number of electrons; Z number of protons and A – Z number of 
neutrons. 
? The atom is specified by the symbol ZX
A 
where X is the chemical symbol for the 
element. 
Solution 4. 
Atomic number Z = 11 
Mass number A = 23 
Number of neutrons A – Z = 12 
 
Chapter 12 - Radioactivity
Solution 5. 
Isotopes: the atoms of the same element which have the same atomic number Z but 
differ in their mass number A are called isotopes. 
 
Solution 6. 
Isobars: the atoms of different elements which have the same mass number A, but 
differ in their atomic number Z are called isobars. 
 
Solution 7. 
 
Solution 8. 
Radioactivity: Radioactivity is a nuclear phenomenon. It is the process of spontaneous 
emission of a or ß and ? radiations from the nuclei of atoms during their decay. 
Example: uranium, radium. 
Solution 9. 
There will be no change in the nature of radioactivity. This is because radioactivity is a 
nuclear phenomenon. 
Solution 10. 
(a) Three types of radiations: Alpha, beta and gamma. 
(b) Alpha and beta radiations 
(c) Gamma radiations 
(d) Gamma radiations 
(e) Alpha radiations 
(f) Beta radiations 
Solution 11. 
(a) Gamma radiations have zero mass. 
(b) Gamma radiations have the lowest ionizing power. 
(c) Alpha particles have lowest penetrating power. 
(d) Alpha particle has positive charge equal to 3.2 x 10
-19
C and rest mass equal to 4 
times the mass of proton i.e. 6.68 x 10
-27
 kg. 
(e) The gas is Helium. 
 
(f) These radiations come from nucleus of the atom. 
Solution 12. 
? Radiations labeled A, B and C are a, ß and ? respectively. 
? Radiation labeled A is gamma radiation because they have no charge and hence 
under action of magnetic field they go undeflected. 
? Radiation B is alpha radiation because its mass is large and it would be deflected 
less in comparison to beta radiation. The direction of deflection is given by 
Fleming’s left hand rule. Also directions of deflection of alpha and beta radiations 
are opposite as they have opposite charge. 
Page 4


Exercise 12(A) 
Solution 1. 
Three constituent of an atom are: 
1. Electrons: mass is 9.1 x 10
-31 
kg, charge is -1.6 x 10
-19
C 
2. Neutron: mass is 1.6749 x 10
-27
 kg, charge is zero. 
3. Protons: mass is 1.6726 x 10
-27
 kg, charge is +1.6 x 10
-19
 C 
Solution 2. 
Atomic number – the number of protons in the nucleus is called atomic number. 
Mass number – the total number of nucleons in the nucleus is called mass number. 
Solution 3. 
? The nucleus at the centre of atom, whose size is of the order of 10
-15
 m to 10
-14
 m. 
? The size of a nucleus is 10
-5
 to 10
-4
 times the size of an atom. It consists of protons 
and neutrons. 
? If Z is the atomic number and A is the mass number of an atom, then the atom 
contains Z number of electrons; Z number of protons and A – Z number of 
neutrons. 
? The atom is specified by the symbol ZX
A 
where X is the chemical symbol for the 
element. 
Solution 4. 
Atomic number Z = 11 
Mass number A = 23 
Number of neutrons A – Z = 12 
 
Chapter 12 - Radioactivity
Solution 5. 
Isotopes: the atoms of the same element which have the same atomic number Z but 
differ in their mass number A are called isotopes. 
 
Solution 6. 
Isobars: the atoms of different elements which have the same mass number A, but 
differ in their atomic number Z are called isobars. 
 
Solution 7. 
 
Solution 8. 
Radioactivity: Radioactivity is a nuclear phenomenon. It is the process of spontaneous 
emission of a or ß and ? radiations from the nuclei of atoms during their decay. 
Example: uranium, radium. 
Solution 9. 
There will be no change in the nature of radioactivity. This is because radioactivity is a 
nuclear phenomenon. 
Solution 10. 
(a) Three types of radiations: Alpha, beta and gamma. 
(b) Alpha and beta radiations 
(c) Gamma radiations 
(d) Gamma radiations 
(e) Alpha radiations 
(f) Beta radiations 
Solution 11. 
(a) Gamma radiations have zero mass. 
(b) Gamma radiations have the lowest ionizing power. 
(c) Alpha particles have lowest penetrating power. 
(d) Alpha particle has positive charge equal to 3.2 x 10
-19
C and rest mass equal to 4 
times the mass of proton i.e. 6.68 x 10
-27
 kg. 
(e) The gas is Helium. 
 
(f) These radiations come from nucleus of the atom. 
Solution 12. 
? Radiations labeled A, B and C are a, ß and ? respectively. 
? Radiation labeled A is gamma radiation because they have no charge and hence 
under action of magnetic field they go undeflected. 
? Radiation B is alpha radiation because its mass is large and it would be deflected 
less in comparison to beta radiation. The direction of deflection is given by 
Fleming’s left hand rule. Also directions of deflection of alpha and beta radiations 
are opposite as they have opposite charge. 
Solution 13. 
 
Solution 14. 
 
(b) The radioactive substances are kept in thick lead containers with a very narrow 
opening, so as to stop radiations coming out from other directions because they may 
cause biological damage. 
Solution 15. 
This is because alpha and beta particles are charged particles, but gamma rays are 
neutral particles. 
 
Page 5


Exercise 12(A) 
Solution 1. 
Three constituent of an atom are: 
1. Electrons: mass is 9.1 x 10
-31 
kg, charge is -1.6 x 10
-19
C 
2. Neutron: mass is 1.6749 x 10
-27
 kg, charge is zero. 
3. Protons: mass is 1.6726 x 10
-27
 kg, charge is +1.6 x 10
-19
 C 
Solution 2. 
Atomic number – the number of protons in the nucleus is called atomic number. 
Mass number – the total number of nucleons in the nucleus is called mass number. 
Solution 3. 
? The nucleus at the centre of atom, whose size is of the order of 10
-15
 m to 10
-14
 m. 
? The size of a nucleus is 10
-5
 to 10
-4
 times the size of an atom. It consists of protons 
and neutrons. 
? If Z is the atomic number and A is the mass number of an atom, then the atom 
contains Z number of electrons; Z number of protons and A – Z number of 
neutrons. 
? The atom is specified by the symbol ZX
A 
where X is the chemical symbol for the 
element. 
Solution 4. 
Atomic number Z = 11 
Mass number A = 23 
Number of neutrons A – Z = 12 
 
Chapter 12 - Radioactivity
Solution 5. 
Isotopes: the atoms of the same element which have the same atomic number Z but 
differ in their mass number A are called isotopes. 
 
Solution 6. 
Isobars: the atoms of different elements which have the same mass number A, but 
differ in their atomic number Z are called isobars. 
 
Solution 7. 
 
Solution 8. 
Radioactivity: Radioactivity is a nuclear phenomenon. It is the process of spontaneous 
emission of a or ß and ? radiations from the nuclei of atoms during their decay. 
Example: uranium, radium. 
Solution 9. 
There will be no change in the nature of radioactivity. This is because radioactivity is a 
nuclear phenomenon. 
Solution 10. 
(a) Three types of radiations: Alpha, beta and gamma. 
(b) Alpha and beta radiations 
(c) Gamma radiations 
(d) Gamma radiations 
(e) Alpha radiations 
(f) Beta radiations 
Solution 11. 
(a) Gamma radiations have zero mass. 
(b) Gamma radiations have the lowest ionizing power. 
(c) Alpha particles have lowest penetrating power. 
(d) Alpha particle has positive charge equal to 3.2 x 10
-19
C and rest mass equal to 4 
times the mass of proton i.e. 6.68 x 10
-27
 kg. 
(e) The gas is Helium. 
 
(f) These radiations come from nucleus of the atom. 
Solution 12. 
? Radiations labeled A, B and C are a, ß and ? respectively. 
? Radiation labeled A is gamma radiation because they have no charge and hence 
under action of magnetic field they go undeflected. 
? Radiation B is alpha radiation because its mass is large and it would be deflected 
less in comparison to beta radiation. The direction of deflection is given by 
Fleming’s left hand rule. Also directions of deflection of alpha and beta radiations 
are opposite as they have opposite charge. 
Solution 13. 
 
Solution 14. 
 
(b) The radioactive substances are kept in thick lead containers with a very narrow 
opening, so as to stop radiations coming out from other directions because they may 
cause biological damage. 
Solution 15. 
This is because alpha and beta particles are charged particles, but gamma rays are 
neutral particles. 
 
Solution 16. 
No, it is not possible to deflect gamma radiation in a way similar to alpha and beta 
particles, using the electric or magnetic field because they are neutral and hence do not 
deflected under the action of electric or magnetic field. 
Solution 17. 
Property a-particle ß-particle ?-particle 
Nature Stream of positively 
charged particles, i.e. 
helium nuclei. 
Stream of negatively 
charged particles, i.e. 
energetic electrons. 
Highly energetic 
electromagnetic radiation. 
Charge Positive charge (Two 
times that of a proton) 
= + 3.2 x 10-19 C (or 
+2e) 
Negative charge = – 1.6 
x 10-19 C (or -e) 
No charge 
Mass Four times the mass of 
proton i.e., 6.68 x 10-
27 kg 
Equal to the mass of 
electron, i.e. 9.1 x 10-
31 kg 
No mass (Rest mass is 
zero) 
Effect of electric field Less deflected More deflected than 
alpha particles but in 
direction opposite to 
those of a particles 
Unaffected 
Solution 18. 
Ionizing power of alpha radiation is maximum i.e., 10000 times of gamma radiation 
while beta particles have lesser ionizing power i.e., 100 times of gamma radiation and 
gamma radiation have least ionizing power. 
Penetration power is least for alpha particle and maximum for gamma radiation. 
Solution 19. 
? Speed of a radiation is nearly 10
7
 m/s. 
? Speed of ß radiation is about 90% of the speed of light or 2.7 x 10
8
 m/s. 
? Speed of ? radiation is 3 x 10
8
 m/s in vacuum. 
Solution 20. 
? Alpha radiations are composed two protons and two neutrons. 
? Beta particles are fast moving electrons. 
? Gamma radiations are photons or electromagnetic waves like X rays. 
? Alpha radiations have the least penetrating power.