81. Define self – inductance and give its S.I. unit.
82. Derive an expression for self inductance of a long, air-cored solenoid of length l, radius r and having N number of turns.
83. Name the radiations of electromagnetic spectrum which are used in
    1. Warfare to look through fog.
    2. Radar and geostationary satellites.
    3. Studying the structure and properties of atoms and molecules.
    4. To photograph internal parts of a human body.
84. The work function of cesium metal is 2 .14 eV. When light of frequency 6 x 10 14 Hz is incident on the metal surface, photoemission of electrons occurs. What is theMaximum kinetic energy of the emitted electrons.
85. An electron beam projected along +X axis, experiences a force due to a magnetic field along the + Y- axis. What is the direction of the magnetic field?
86. The instantaneous current from an ac source is I = 6 sin 314t. What is the rms value of the current?
87. A bulb connected in series with a solenoid is lit by ac source. If a soft iron core is introduced in the solenoid, will the bulb glow brighter?
88. Which part of the electromagnetic spectrum is used in operating RADAR? Give its wavelength range.
89. Two thin lenses + 6D and -2D are in contact. What is the focal length of the combination?
90. The ionization potential of hydrogen is 13.6 V. calculate the energy of its first excited state.
91. How does the collector current change in a junction transistor, if the base region has larger width?
92. How does the conductivity change of a semiconductor with increase of temperature?
93. Define the term temperature coefficient of resistivity. Draw a graph showing the variation of reistivity with temperature for copper.
94. S₁and S₂are two hollow concentric sphere enclosing charges Q and 2Q respectively as shown in fig.What is the ratio of electric flux through S₁& S₂?
95. How will the electric flux through the sphere change, if a medium of dielectric constant 5 is introduced in the space inside S₁in place of air?
96. Two cells E₁and E₂in the given circuit diagram have an emf of 4V and 8V and internal resistance 0.5W and 1.0W respectively. Calculate the current flowing through the resistance of 3W.
97. How will a dia & ferro magnetic material behave when kept in a non-uniform external field? Give two examples each.
98. Write two applications of each, microwaves and infrared rays.
99. A double concave lens of glass of RI 1.6 has radii of curvature of 40cm, 60cm. Calculate its focal length. Also find the focal length of the lens if the lens is immersed in a liquid of RI 1.3.
100. Show that the de-Broglie wavelength l of electrons of energy E is given by the relation l =
101. An electrical element x, when connected to an alternating voltage source, has the current through it leading the voltage by π/2 radii. Identify x and write an expression for its reactance.
102. Identify the logic gate 1 and 2 in the logic circuit given. Also, write the truth table for the final output for all possible combination of inputs A and B.
103. A
     1. Ч1 Ч2
     2. B
104. What is the angle between the directions of electric field at any
     1. axial point and
     2. equitorial point due to an electric dipole?
105. Whay should the spring/suspension wire in a moving coil galvanometer have low torsional constant?