Plus Two Physics Chapter Wise Previous Questions Chapter 13 Nuclei is part of Kerala Plus Two Physics Chapter Wise Previous Questions and Answers Kerala. Here we have given Plus Two Physics Chapter Wise Questions and Answers Chapter 13 Nuclei.

## Kerala Plus Two Physics Chapter Wise Previous Questions and Answers Chapter 13 Nuclei

Question 1.

How many electrons, protons and neutrons are there in 16g of _{8}O^{16}?** [March-2018]
**Answer:

16 g of oxygen contains

N

_{A}no.of atoms

N

_{a}= 6.025 × 10

^{23 }N

_{p}= 8 × 6.025 ×10

^{23 }N = 8 × 6.025 × 10

^{23 }N

_{n}= (16-8)× 6.025 × 10

^{23 }i.e., N = N = N = 8 × 6.025 × 10

^{23 }= 48.2 × 10

^{23}

Question 2.

a. State radioactive decay law.

b. Prove the relation N(t)= N_{0}e^{λt }**[March-2018]
**Answer:

a. Law of radioactive Decay. According to this law, the rate of decay of radioactive atoms at any instant is proporational o the number of atoms present at that instant in the sample.

where X = decay constant and N = number of undisintegrated nucleus present in the sample at any time t.

N = N

_{0}e

^{-λt}; N

_{0}= initial amount.

b.

Question 3.

a. Define half life period of a radioactive nucleus. Write down the relation connecting half life period and mean life.

b. Define 1 amu. Calculate its energy equivalent in MeV. **[March-2017]
**Answer:

a. Half life(T

_{1/2}) is the time taken for half of the number of atoms in the sample to decay.

Mean life is defined as the time taken by the sample to reduce to 1/e

^{th}of its initial value.

b. The unit in which atomic and nuclear masses are measured is called atomic mass unit (a.m.u). 1 amu is defined as 1/12

^{th}of the mass of an atom of

_{6}C

^{12}isotope.

It can be shown that 1 amu= 1.66 ×10

^{27 }kg

According to einstein mass energy equivalence E = mC

^{2 }Where m = 1.66 x 10

^{-27}kg, C = 3 × 10

^{8}ms

Question 4.

a. What do you mean by Q value of a nuclear reaction?

b. Write down the expression for Q value in the case of a

c. Two nuclei have mass numbers in the ratio 1 : 64. What is the ratio of their nuclear radii ?** [March-2016]
**Answer:

a. The disintegration energy or the Q- value of a nuclear reaction is the difference between the initial mass energy and the total mass energy of the decay products.

b. For a-decay

Question 5.

i. Obtain an expression for the number of radioactive nuclei present at any instant in terms of the decay constant and initial nunber of nuclei.

ii. The half life of radioactive radon is 3.8 days. Find the time during which 1/20 of radon sample will remain undecayed. **[March-2015]
**Answer:

Question 6.

Though energy released per fission is greater than that of fusion, fusion is preferred over fission. Why? **[March-2014]**

Answer:

In a nuclear fusion reaction the energy liberated per unit mass of the nuclei taking part in the reaction is many times larger than the energy liberated in a fission reaction.

Question 7.

In a nuclear reactor the chain reaction is carried out under controlled conditions.

a. Name the material that is used as control rods in a nuclear reactor.

b. Average energy of a Neutron produced in fission of _{92}U^{235} nucleus is…………. **[March-2013]
**Answer:

a. Cadmium / Boron

b. 2 MeV

Question 8.

a. In the following nuclear fission reaction N is the number of neutrons emitted. What is the value of N ?

b. Complete the following nuclear reaction

c. Two nuclei have mass numbers in the ratio 1:8. What is the ratio of their nuclear radii? ** [March-2012]
**Answer:

a. 2 neutrons.

Question 9.

Radioactivity is the phenomenon of spontaneous emission of alpha,beta and gamma by certain unstable nuclei. If a radioactive nucleus z undergoes a-decay series according to the following scheme.

If the mass number and atomic number of Z_{s} are 178 and 72 respectively, then what will be the mass number and atomic number of Z?

b. Do you think radioactive decay is similar to ordinary chemical reaction? Justify your answer.

** [March-2010]
**Answer:

a. Atomic number = 74

Mass number =186

b.No. In chemical reaction only valance electrons are involved. But radioactivity is a spontaneous process associated with decay of nucleus.

Question 10.

When a U^{235} nuclear captures a slow neutron, a fission results with a release of 200 Mev energy, then

a. How does this enormous energy results?

b. If the output of a nuclear reactor is 3.2 MW, what is the rate at which U^{235} nuclei undergo fission?

**[March-2010]
**Answer:

a. Mass defect [the difference in mass] is converted into this energy as E = Δmc

^{2 }b.Given that, output power = 3.2 MW = 3.2 × 10

^{6}

We know, the energy released per fission is 200 MeV.

So the number of fission per second,

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