Atoms, Molecules and Nuclei Test

Result

Atoms, Molecules and Nuclei Test - 3

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Weekly Quiz Competition

Question 1
1 / -0

A freshly prepared radioactive source of half-life 2 hours emits radiation of intensity which is 64 times the permissible safe level. The minimum time after which it would be possible to work safely with this source is

A
6 hours

B
12 hours

C
24 hours

D
128 hours

Solution

The radioactivity of a sample decreases to (1/2ⁿ) in 'n' half lives. Since the initial activity is 64 times the permissible level, it must become 1/64^thof its initial value.

∴ 1/64 = 1/2ⁿ or n = 6

In other words, in six half-lives, the activity will reduce itself to the permissible level. Since half-life is 2 hours, the total time taken = 2 × 6 h = 12 hours.
Question 2
1 / -0

Consider α particles, β particles and γ rays, each having energy of 0.5 MeV. In the increasing order of penetrating power, the radiations are

A
α,β,γ

B
α,γ,β

C
β,γ,α

D
γ,β,α

Solution

As the energies of alpha particles, beta particles and gamma rays are same, the velocity of alpha particles is least among the given particles as the mass of the alpha particle is 1840 times the mass of the electrons (beta particles), whereas the gamma rays are photons.
As the greater the velocity, the greater is the penetrating power; gamma rays have the greatest penetrating power and alpha particles have the least penetrating power.
Question 3
1 / -0

In the fission of one part of uranium, if 0.5 gm mass is decayed, then how much energy (in kWh) will be obtained?

A
1.25 × 10⁷

B
1.5 × 10⁵

C
2.25 × 10⁷

D
4.5 × 10⁷

Solution

E = mc²= (0.5 × 10^-3) (3 × 10⁸)² = 4.5 × 10¹³ J = 4.5 × 10¹³/(60 × 60) = 1.25 × 10⁷kWh
Question 4
1 / -0

Assertion (A): Nuclear forces arise from strong Coulombic interactions between protons and neutrons.
Reason (R): Nuclear forces are independent of the charge of the nucleons.

A
Both (A) and (B) are true and (R) is the correct explanation of (A).

B
Both (A) and (B) are true, but (R) is not the correct explanation of (A).

C
(A) is true, but (R) is false.

D
(A) is false, but (R) is true.

Solution

The strong nuclear force is created between nucleons by the exchange of particles called mesons. If it were due to Coulombic forces, then there would be strong repulsion between protons inside the nucleus; thereby the nucleus would have not existed. Nuclear force never depends on the charge of nucleons; it depends on exchange of particles called mesons.