Science (English Medium) Class 12 - CBSE Question Bank Solutions

 Is the formula you employ in (a) valid for calculating radius of the path of a 20 MeV electron beam? If not, in what way is it modified?

An electron gun with its collector at a potential of 100 V fires out electrons in a spherical bulb containing hydrogen gas at low pressure (∼10⁻² mm of Hg). A magnetic field of 2.83 × 10⁻⁴ T curves the path of the electrons in a circular orbit of radius 12.0 cm. (The path can be viewed because the gas ions in the path focus the beam by attracting electrons, and emitting light by electron capture; this method is known as the ‘fine beam tube’ method. Determine e/m from the data.

What is so special about the combination e/m? Why do we not simply talk of e and m separately?

A difference of 2.3 eV separates two energy levels in an atom. What is the frequency of radiation emitted when the atom makes a transition from the upper level to the lower level?

The ground state energy of a hydrogen atom is −13.6 eV. What are the kinetic and potential energies of the electron in this state?

A hydrogen atom initially in the ground level absorbs a photon, which excites it to the n = 4 level. Determine the wavelength and frequency of the photon.

The total energy of an electron in the first excited state of the hydrogen atom is about −3.4 eV.

What is the kinetic energy of the electron in this state?

The total energy of an electron in the first excited state of the hydrogen atom is about −3.4 eV.

What is the potential energy of the electron in this state?

The total energy of an electron in the first excited state of the hydrogen atom is about −3.4 eV.

Which of the answers above would change if the choice of the zero of potential energy is changed?

Obtain the first Bohr’s radius and the ground state energy of a muonic hydrogen atom [i.e., an atom in which a negatively charged muon (μ⁻) of mass about 207 m_e orbits around a proton].

In an unbiased p-n junction, holes diffuse from the p-region to n-region because ______.

In a p-n junction diode, the current I can be expressed as

I = `"I"_0 exp ("eV"/(2"k"_"BT") - 1)`

where I₀ is called the reverse saturation current, V is the voltage across the diode and is positive for forward bias and negative for reverse bias, and I is the current through the diode, k_Bis the Boltzmann constant (8.6×10⁻⁵ eV/K) and T is the absolute temperature. If for a given diode I₀ = 5 × 10⁻¹² A and T = 300 K, then

(a) What will be the forward current at a forward voltage of 0.6 V?

(b) What will be the increase in the current if the voltage across the diode is increased to 0.7 V?

(c) What is the dynamic resistance?

(d) What will be the current if reverse bias voltage changes from 1 V to 2 V?

Define self-inductance of a coil.

Write the two processes that take place in the formation of a p-n junction.

Explain two features to distinguish between the interference pattern in Young's double slit experiment with the diffraction pattern obtained due to a single slit.

A monochromatic light of wavelength 500 nm is incident normally on a single slit of width 0.2 mm to produce a diffraction pattern. Find the angular width of the central maximum obtained on the screen.

Estimate the number of fringes obtained in Young's double slit experiment with fringe width 0.5 mm, which can be accommodated within the region of total angular spread of the central maximum due to single slit.

A zener diode is fabricated by heavily doping both p- and n- sides of the junction. Explain, why?

Explain briefly with the help of necessary diagrams, the forward biasing of a p-n junction diode. Also draw characteristic curves.

Explain briefly with the help of necessary diagrams, the  reverse biasing of a p-n junction diode. Also draw characteristic curves.

Obtain the expression for the magnetic energy stored in an inductor of self-inductance L to build up a current I through it.