Science (English Medium) Class 12 - CBSE Important Questions

How long can an electric lamp of 100 W be kept glowing by fusion of 2 kg of deuterium? Take the fusion reaction as 

\[\ce{​​^2_1H + ^2_1H -> ^3_2He + n + 3.27 MeV}​​\]

The radius of the innermost electron orbit of a hydrogen atom is 5.3 × 10^–11m. The radius of the n = 3 orbit is ______.

What is the nuclear radius of ¹²⁵Fe, if that of ²⁷Al is 3.6 fermi?

The short wavelength limit for the Lyman series of the hydrogen spectrum is 913.4 Å. Calculate the short wavelength limit for the Balmer series of the hydrogen spectrum.

The ground state energy of hydrogen atoms is -13.6 eV. The photon emitted during the transition of electron from n = 3 to n = 1 unknown work function. The photoelectrons are emitted from the material with a maximum kinetic energy of 9 eV. Calculate the threshold wavelength of the material used.

How will the energy of a hydrogen atom change if n increases from 1 to ∞?

An electron in a hydrogen atom makes transitions from orbits of higher energies to orbits of lower energies.

1. When will such transitions result in (a) Lyman (b) Balmer series?
2. Find the ratio of the longest wavelength in the Lyman series to the shortest wavelength in the Balmer series.

The energy of hydrogen atom in an orbit is −1.51 eV. What are the kinetic and potential energies of the electron in this orbit?

The electron in a hydrogen atom is typically found at a distance of about 5.3 × 10⁻¹¹ m from the nucleus which has a diameter of about 1.0 × 10⁻¹⁵ m. Assuming the hydrogen atom to be a sphere of radius 5.3 × 10⁻¹¹ m, what fraction of its volume is occupied by the nucleus?

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.