Science (English Medium) Class 12 - CBSE Important Questions

Distinguish between nuclear fission and fusion. Show how in both these processes energy is released. Calculate the energy release in MeV in the deuterium-tritium fusion reaction :

`""_1^2H+_1^3H->_2^4He+n`

Using the data :

m(`""_1^2H`) = 2.014102 u

m(`""_1^3H`) = 3.016049 u

m(`""_2^4He`) = 4.002603 u

m_n = 1.008665 u

1u = 931.5 MeV/c²

Draw the plot of binding energy per nucleon (BE/A) as a functino of mass number A. Write two important conclusions that can be drawn regarding the nature of nuclear force.

Show that the density of nucleus over a wide range of nuclei is constant-independent of mass number A.

Distinguish between nuclear fission and fusion giving an example of each.

The ratio of the nuclear densities of two nuclei having mass numbers 64 and 125 is ______.

Distinguish between 'intrinsic' and 'extrinsic' semiconductors

Explain, with the help of a circuit diagram, the working of a photo-diode. Write briefly how it is used to detect the optical signals.

Mention the important considerations required while fabricating a p-n junction diode to be used as a Light Emitting Diode (LED). What should be the order of band gap of an LED if it is required to emit light in the visible range?

The graph shown in the figure represents a plot of current versus voltage for a given semiconductor. Identify the region, if any, over which the semiconductor has a negative resistance.

Show on a graph, the variation of resistivity with temperature for a typical semiconductor.

What is meant by doping of an intrinsic semiconductor?

Name the two types of atoms used for doping of Ge/Si.

In an extrinsic semiconductor, the number density of holes is 4 × 10²⁰ m^-3. If the number density of intrinsic carriers is 1.2 × 10¹⁵ m^-3, the number density of electrons in it is ______.

The formation of the depletion region in a p-n junction diode is due to ______.

Draw an energy band diagram for a p-type semiconductor at T > 0 K.

Draw the circuit arrangement for studying V-I characteristics of a p-n junction diode in (i) forward biasing and (ii) reverse biasing. Draw the typical V-I characteristics of a silicon diode.

Define modulation index.

How are side bands produced?

Draw a block diagram of a detector for AM signal and show, using necessary processes and the waveforms, how the original message signal is detected from the input AM wave.