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Q1 (a) Two stable isotopes of lithium 6Li3 and7Li3 have respective abundances of 7.5% and 92.5%. These isotopes have masses 6.01512 u and 7.01600 u, respectively. Find the atomic mass of lithium. (b) Boron has two stable isotopes, 10B5 and 11B5 . Their respective masses are 10.01294 u and 11.00931 u, and the atomic mass of boron is 10.811 u. Find the abundances of 10B5 and 11B5. Ans: (a) Mass of 6Li3, lithium isotope, m 1 = 6.01512 u
Mass of 7Li3, lithium isotope, m = 7.01600 u
Abundance of 6Li3 , η1 = 7.5%
Abundance of 7Li3 , η2 = 92.5%
The atomic mass of lithium atom is given as:
( b ) Mass of boron isotope 10B5 , m = 10.01294 u
Mass of boron isotope 11B5 , m = 11.00931 u
Abundance of 10B5, η1 = x %
Abundance of 11B5, η2 = (100 − x ) %
Atomic mass of boron, m = 10.811 u The atomic mass of boron atom is given as:
And 100 − x = 80.11%
Hence, the abundance of is 10B5 19.89% and that of 11B5 is 80.11%.
Q2 The three stable isotopes of neon: 20Ne10, 21Ne10 and 22Ne10 have respective abundances of 90.51%, 0.27% and 9.22%. The atomic masses of the three isotopes are 19.99 u, 20.99 u and 21.99 u, respectively. Obtain the average atomic mass of neon. Ans: Atomic mass of 20Ne10, m1 = 19.99 u
Abundance of 20Ne10, η1 = 90.51%
Atomic mass of 21Ne10, m2 = 20.99 u
Abundance of 21Ne10, η2 = 0.27%
Atomic mass of 22Ne10, m3 = 21.99 u
Abundance of 22Ne10, η3 = 9.22%
The average atomic mass of neon is given as:
Chapter 13 Nuclei
The thirteenth chapter of NCERT Physics for Class 12 teaches about the nuclei. This chapter explains about the nucleus of an atom and energy, kits size, force, atomic masses, radioactivity, radioactive particles and their properties, and radioactive decay law, isotopes, isobars, isotones, the mass-energy relation, nuclear fission, fusion, the radioactivity properties, etc.
Download pdf of NCERT Solutions for Class Physics Chapter 13 Nuclei
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Exercise 1
Popular Questions of Class 12 Physics
- Q:-
What is the force between two small charged spheres having charges of 2 x 10-7 C and 3 x 10-7 C placed 30 cm apart in air?
- Q:-
An infinite line charge produces a field of 9 × 104 N/C at a distance of 2 cm. Calculate the linear charge density.
- Q:-
A polythene piece rubbed with wool is found to have a negative charge of 3 × 10−7 C.
(a) Estimate the number of electrons transferred (from which to which?)
(b) Is there a transfer of mass from wool to polythene?
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A 600 pF capacitor is charged by a 200 V supply. It is then disconnected from the supply and is connected to another uncharged 600 pF capacitor. How much electrostatic energy is lost in the process?
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A parallel plate capacitor with air between the plates has a capacitance of 8 pF (1pF = 10-12 F). What will be the capacitance if the distance between the plates is reduced by half, and the space between them is filled with a substance of dielectric constant 6?
- Q:- A circular coil of wire consisting of 100 turns, each of radius 8.0 cm carries a current of 0.40 A. What is the magnitude of the magnetic field B at the centre of the coil?
- Q:-
A regular hexagon of side 10 cm has a charge 5 µC at each of its vertices. Calculate the potential at the centre of the hexagon.
- Q:-
A point charge +10 μC is a distance 5 cm directly above the centre of a square of side 10 cm, as shown in Fig. 1.34. What is the magnitude of the electric flux through the square? (Hint: Think of the square as one face of a cube with edge 10 cm.)
- Q:-
A conducting sphere of radius 10 cm has an unknown charge. If the electric field 20 cm from the centre of the sphere is 1.5 × 103 N/C and points radially inward, what is the net charge on the sphere?
- Q:-
A point charge of 2.0 μC is at the centre of a cubic Gaussian surface 9.0 cm on edge. What is the net electric flux through the surface?
Recently Viewed Questions of Class 12 Physics
- Q:-
A p-n photodiode is fabricated from a semiconductor with band gap of 2.8 eV. Can it detect a wavelength of 6000 nm?
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What is the shortest wavelength present in the Paschen series of spectral lines?
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(a) Three resistors 1 Ω, 2 Ω, and 3 Ω are combined in series. What is the total resistance of the combination?
(b) If the combination is connected to a battery of emf 12 V and negligible internal resistance, obtain the potential drop across each resistor.
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(a) The refractive index of glass is 1.5. What is the speed of light in glass? (Speed of light in vacuum is 3.0 × 10 8 m s -1 )
(b) Is the speed of light in glass independent of the colour of light? If not, which of the two colours red and violet travels slower in a glass prism?
- Q:- (a) Explain the meaning of the statement electric charge of a body is quantised.
(b) Why can one ignore quantisation of electric charge when dealing with macroscopic i.e., large scale charges? - Q:-
Two concentric circular coils X and Y of radii 16 cm and 10 cm, respectively, lie in the same vertical plane containing the north to south direction. Coil X has 20 turns and carries a current of 16 A; coil Y has 25 turns and carries a current of 18 A. The sense of the current in X is anticlockwise, and clockwise in Y, for an observer looking at the coils facing west. Give the magnitude and direction of the net magnetic field due to the coils at their centre.
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A 12.5 eV electron beam is used to bombard gaseous hydrogen at room temperature. What series of wavelengths will be emitted?
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The work function for a certain metal is 4.2 eV. Will this metal give photoelectric emission for incident radiation of wavelength 330 nm?
- Q:- What is the focal length of a convex lens of focal length 30 cm in contact with a concave lens of focal length 20 cm? Is the system a converging or a diverging lens? Ignore thickness of the lenses.
- Q:-
In Exercise, obtain the frequency of revolution of the electron in its circular orbit. Does the answer depend on the speed of the electron? Explain.
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