Science (English Medium) कक्षा १२ - CBSE Important Questions for Physics

Specify the transition of an electron in the wavelength of the line in the Bohr model of the hydrogen atom which gives rise to the spectral line of the highest wavelength ______.

Differentiate between the 'distance of the closest approach' and the 'impact parameter.'

Determine the distance of the closest approach when an alpha particle of kinetic energy 3.95 MeV approaches a nucleus of Z = 79, stops and reverses its directions.

State three postulates of Bohr's theory of hydrogen atom.

Find the angular momentum of an electron revolving in the second orbit in Bohr's hydrogen atom.

The wavelength of the second line of the Balmer series in the hydrogen spectrum is 4861 Å. Calculate the wavelength of the first line of the same series.

When alpha particles are sent through a thin gold foil, most of them go straight through the foil, because ______.

The energy of an electron in the n^th orbit of the hydrogen atom is E_n = -13.6/n²eV. The negative sign of energy indicates that ______.

(a) Write the basic nuclear process involved in the emission of β⁺ in a symbolic form, by a radioactive nucleus.

(b) In the reactions given below:

(i)`""_16^11C->_y^zB+x+v`

(ii)`""_6^12C+_6^12C->_a^20 Ne + _b^c He`

Find the values of x, y, and z and a, b and c.

How is the mean life of a given radioactive nucleus related to the decay constant?

Write symbolically the nuclear β⁺ decay process of `""_6^11C` Is the decayed product X an isotope or isobar of (`""_6^11C`)? Given the mass values m (`""_6^11C`) = 11.011434 u and m (X) = 11.009305 u. Estimate the Q-value in this process.

(a) Derive the relation between the decay constant and half life of a radioactive substance. 
(b) A radioactive element reduces to 25% of its initial mass in 1000 years. Find its half life.

Define 'activity' of a radioactive substance ?

Two different radioactive elements with half lives T₁ and T₂ have N₁ and N₂ undecayed atoms respectively present at a given instant. Derive an expression for the ratio of their activities at this instant in terms of N₁ and N_{2 ?}

Write the β-decay of tritium in symbolic form.

Why is it experimentally found difficult to detect neutrinos in this process ?

What is the significance of negative sign in the expression for the energy?

Write any two characteristic properties of nuclear force.

Using the curve for the binding energy per nucleon as a function of mass number A, state clearly how the release in energy in the processes of nuclear fission and nuclear fusion can be explained.

A heavy nucleus X of mass number 240 and binding energy per nucleon 7.6 MeV is split into two fragments Y and Z of mass numbers 110 and 130. The binding energy of nucleons in Y and Z is 8.5 MeV per nucleon. Calculate the energy Q released per fission in MeV.