Question 61:
easyAssertion (A): More energy is released in fusion than fission per nucleon.
Reason (R): More number of nucleons takes part in fusion.
Assertion (A) is true; fusion releases significantly more energy per nucleon than fission. Reason (R) is false; fusion involves lighter nuclei (fewer nucleons) compared to fission.
The higher energy release per nucleon is due to the greater increase in binding energy per nucleon.
Question 62:
easyAssertion (A): Deuterium is a good moderator of fast neutrons.
Reason (R): Fast neutrons transfer 90% of their kinetic energy to the nuclei of the moderator in an elastic collision.
Assertion (A) is true. Deuterium's mass is close to a neutron's, making it efficient for moderation. Reason (R) is true; in elastic collision with deuterium, neutrons lose about 89% of their kinetic energy. (R) is the correct explanation for (A).
Question 63:
easyAssertion (A): Beryllium can be used as a moderator in nuclear fission reactor.
Reason (R): A fast moving electron on collision with a light stationary particle loses most of its energy in nuclear reactor.
Assertion (A) is true; Beryllium is a suitable moderator due to low mass and absorption.
Reason (R) is false; moderation involves neutrons, not electrons. Electrons are not used for moderating neutrons in nuclear reactors. Thus, (A) is true, but (R) is false.
Question 64:
easyAssertion (A): Nuclear force is short range while gravitation and electric force are universal.
Reason (R): Nuclear force does not follow inverse square law.
Assertion (A) is true; nuclear force is short-range, while gravitational and electric forces are long-range.
Reason (R) is true; nuclear force has a complex dependence, not \(1/r^2\). (R) correctly explains (A) as the absence of inverse square law behavior is characteristic of short-range forces.
Question 65:
easyAssertion (A): Energy is released when heavy nuclei undergo fission or light nuclei undergo fusion.
Reason (R): For heavy nuclei, binding energy per nucleon increases with increasing (Z) while for light nuclei, it decreases with increasing (Z).
Assertion (A) is true as both fission and fusion release energy. Reason (R) is false because binding energy per nucleon for heavy nuclei decreases with increasing (Z) (after Fe) and increases for light nuclei (up to Fe). Thus, (A) is true, (R) is false.
Question 66:
easyAssertion (A): Size of nucleus determined electron scattering and (alpha)-scattering are same.
Reason (R): Electron scattering or by (alpha)-scattering is controlled by distribution of charge in nucleus.
Assertion (A) is true; both methods estimate nuclear size based on charge distribution. Reason (R) is true; both electron and alpha scattering probe nuclear charge distribution. (R) correctly explains (A) as the interaction with charge distribution determines the 'size' measured.
Question 67:
easyAssertion (A): It is very easy to detect neutrino in nature.
Reason (R): It has high affinity to interact with matter.
Assertion (A) is false; neutrinos are extremely difficult to detect due to very weak interactions. Reason (R) is also false; neutrinos have very low affinity to interact with matter. Therefore, both (A) and (R) are false.
Question 68:
moderateGiven below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): \(\text{Fe}^{56}\) nucleus is more stable than \(\text{U}^{235}\) nucleus.
Reason (R): Binding energy of \(\text{Fe}^{56}\) nucleus is more than the binding energy of \(\text{U}^{235}\).
In the light of the above statements, choose the correct answer from the option given below.
\(\text{Fe}^{56}\) is more stable because its binding energy per nucleon is higher than that of \(\text{U}^{235}\). However, the total binding energy of \(\text{U}^{235}\) is greater than that of \(\text{Fe}^{56}\) because it contains many more nucleons. Hence, Assertion is true but Reason is false.
Question 69:
easyA nucleus of nuclear density \(\rho\) disintegrates into two daughter nuclei with masses in the ratio 9:21. Density of the smaller nucleus is
Nuclear density is constant and independent of mass number \(A\) because mass is proportional to \(A\) and volume is also proportional to \(A\). Thus, the density remains \(\rho\).
Question 70:
easyConsider the following statements:
a. The density of the nuclear matter is independent of the size of the nucleus.
b. Fusion of light nuclei to form heavier nuclei is possible at room temperature.
c. Electron and positron are particle-antiparticle pair.
The correct statement(s) is/are
Nuclear density is constant for all nuclei, hence independent of size (Statement a is true). Nuclear fusion requires extremely high temperatures (Statement b is false). Positron is the antiparticle of electron (Statement c is true).