11. What is mass defect? Give its expression. (MAR 25)
12. What is meant by radioactivity?
13.What is mean - life of a radioactive nucleus? Give the
expression. (JULY 22)
14. What is half-life of a radioactive nucleus? Give the
expression. (JULY 22)
15. What is meant by activity or decay rate? Give its unit. (MAR
23)
16. Define curie.
17. What are the constituent particles of neutron and proton? (SEP
20)
18. The radius of the 5th orbit of hydrogen atom is 13.25 Å.
Calculate the de broglie wavelength of the electron orbiting in
the 5th orbit. (Example 9.1) (JUNE 23,24)
19. Calculate the radius of 79Au197 nucleus. (Example 9.7) (MAY
22)
20. Calculate the number of nuclei of 𝑐𝑎𝑟𝑏𝑜𝑛−14 undecayed after
22,920 𝑦𝑒𝑎𝑟𝑠 if the initial number of 𝑐𝑎𝑟𝑏𝑜𝑛 − 14 atoms is 10,000.
The half-life of 𝑐𝑎𝑟𝑏𝑜𝑛−14 is 5730𝑦𝑒𝑎𝑟𝑠. (Exam 9.12) (JULY 22)
21. An electron in Bohr‟s hydrogen atom has energy of −3.4𝑒𝑉. What
is the angular momentum of the electron? (MAR 20)
22. The half-life of radioactive sample is 5.01 days. Calculate
the decay constant. (MAR 24)
12th Physics Chapter 9 Important - 3 Marks
1. Write the properties of cathode rays. (JULY 22)
2. Write down the postulates of Bohr atom model.
3. Write down the drawbacks of Bohr atom model.
4. Discuss the alpha decay process with example. (JUNE 23)
5. Discuss the beta decay process with examples. (MAR 24)
6. Discuss the gamma emission process with example.
7. Explain the idea of carbon dating.
8. What are the properties of neutrino? (MAR 20)
9. What are the important inferences from the average binding
energy curve? (MAR 20)
10. What are properties of nuclear force?
11. Calculate the amount of energy released when 1 kg of 235U 92
undergoes fission reaction. (Exam 9.15) (MAR 23)
12. Find the (i) angular momentum (ii) velocity of the electron
revolving in the 5𝑡ℎ orbit of hydrogen atom. (ℎ = 6.6 × 10−34 𝐽𝑠,
𝑚 = 9.1 × 10−31 𝑘𝑔) (Exam- 9.2) (MAY 22,MAR 25)
13. 238𝑈92 nucleus emits 2α particles, 3β particles and 2γ
particles. What is the resulting atomic number and mass number?
(AUG-21)
14. Half-lives of two radioactive elements A and B are 20 minutes
and 40 minutes respectively. Initially, the samples have equal
number of nuclei. Calculate the ratio of decayed numbers of A and
B nuclei after 80 minutes. (Ex-6,CH-9) (SEP 20)
15. Calculate the electrostatic force between the proton and the
electron in a hydrogen atom. They are separated by a distance of
5.3 x 10-11 m. The Magnitude of charges on the electron and proton
are 1.6 × 10-19
12th Physics Chapter 9 Important - 5 Marks
1. Explain the J.J.Thomson experiment to determine the specific
charge of electron. (JUNE 24)
2. Discuss the Millikan‟s oil drop experiment to determine the
charge of an electron.
3. Derive the energy expression for an electron is the hydrogen
atom using Bohr atom model. (MAR 20)
4. Discuss the spectral series of hydrogen atom. (MAY 22)
5. Obtain the law of radioactivity. (AUG 21, JUNE 23,MAR 25)
6. What is nuclear reactor? Write note on Moderators, Control
rods, and Cooling system. (MAR 24)
7. Derive an expression for the radius and velocity of the orbit
of electron in the nth orbit an atom using Bohr atom model. (SEP
20, MAR 23)
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