List of practice Questions

A p-type Si semiconductor is made by doping an average of one dopant atom per \( 5 \times 10^7 \) silicon atoms. If the number density of silicon atoms in the specimen is \( 5 \times 10^{28} \, \text{atoms/m}^3 \), find the number of holes created per cubic centimetre in the specimen due to doping. Also, give one example of such dopants.

Two batteries of emfs 3V and 6V and internal resistances 0.2 and 0.4 are connected in parallel. This combination is connected to a 4 resistor. Find:
(i) the equivalent emf of the combination
(ii) the equivalent internal resistance of the combination
(iii) the current drawn from the combination

When electrons drift in a conductor from lower to higher potential, does it mean that all the ’free electrons’ of the conductor are moving in the same direction?

Define the magnetic moment of a current-carrying coil. Write its SI unit.

A coil of 60 turns and area \( 1.5 \times 10^{-3} \, \text{m}^2 \) carrying a current of 2 A lies in a vertical plane. It experiences a torque of 0.12 Nm when placed in a uniform horizontal magnetic field. The torque acting on the coil changes to 0.05 Nm after the coil is rotated about its diameter by 90°. Find the magnitude of the magnetic field.

Consider two long co-axial solenoids \( S_1 \) and \( S_2 \), each of length \( l \) (\( l \gg r_2 \)) and radius \( r_1 \) and \( r_2 \) (\( r_2>r_1 \)). The number of turns per unit length are \( n_1 \) and \( n_2 \), respectively. Derive an expression for mutual inductance \( M_{12} \) of solenoid \( S_1 \) with respect to solenoid \( S_2 \). Show that \( M_{21} = M_{12} \).

A parallel plate capacitor is charged by an ac source. Show that the sum of conduction current (\( I_c \)) and the displacement current (\( I_d \)) has the same value at all points of the circuit.

In case (a) above, is Kirchhoff's first rule (junction rule) valid at each plate of the capacitor? Explain.

Draw a plot of frequency \( \nu \) of incident radiations as a function of stopping potential \( V_0 \) for a given photoemissive material. What information can be obtained from the value of the intercept on the stopping potential axis?

Calculate: (i) the momentum and (ii) de Broglie wavelength, of an electron with kinetic energy of 80 eV.

Draw circuit arrangement for studying V-I characteristics of a p-n junction diode.

Show the shape of the characteristics of a diode.

Mention two information that you can get from these characteristics.