Unit IX: Electronic Devices
Semiconductors; semiconductor
diode – I-V characteristics in forward and reverse bias, diode as a rectifier; I-V characteristics of LED, photodiode,
solar cell, and Zener diode; Zener diode as a voltage regulator. Junction transistor, transistor action, characteristics of
a transistor; transistor as an amplifier (common emitter configuration) and oscillator. Logic gates (OR, AND, NOT, NAND and
NOR). Transistor as a switch.
Unit X: Communication
Systems :
Elements of a communication system
(block diagram only); bandwidth of signals (speech, TV and digital data); bandwidth of transmission medium. Propagation of
electromagnetic waves in the atmosphere, sky and space wave propagation. Need for modulation. Production and detection of
an amplitude-modulated wave.
1. Explain briefly (i) charge quantization (ii) conservation of charge.
2. Write vector form of coulomb’s law. How force depends
on intervening medium.
3. Define Electric field intensity and electric potential due
to a point charge. Give their S.I. units.
4. Derive expression for electric potential due to a point charge.
5. Define Electric dipole moment and give its unit and direction.
6. Find expression for electric field intensity on axial and
equatorial line of a electric dipole.
7. State Gauss’ theorem . Calculate electric flux due
to surface enclosing charge of 1C.
8. Obtain the expression for the
electric field intensity E due to infinite plane sheet of charge .
9. Derive the expression
for the E at any point outside and inside a uniformly charged spherical shell.
10. Derive an expression for the E at a point near an infinitely long , thin ,uniformly charged straight wire.
11.Find expression for
torque on electric dipole in uniform electric field. Give its equilibrium state.
12. Derive expression for capacitance
of a parallel
plate capacitor i)without dielectric ii)with dielectric slab.
13.Derive expression for energy stored and energy density (½εοE2)
of a charged capacitor.
14.How Voltage, charge , capacity ,energy and electric field
changes when dielectric is introduced
between the plates of capacitor i)with battery connected and ii)without battery.
15. Draw lines of forces for i) q>0 ii)q<0 .Why lines
are not discontinuous and never intersect .
16. What is equipotential surface? Find work done on moving
charge on such surface.
17.Give principle ,construction, working and labeled diagram
of a Vande graff generator. How
charge leakage is prevented.
18. Find charge and voltage on each capacitor
in given circuits.
15µF
┤ ├
(i) ┤
├ ┤ ├
(ii)
┤ ├
10µF
5µF
10µF
┤
├ 10µF
19. A charge q is placed at the centre of line joining two equal
charges Q. Show that the system of three
charges
will be in equilibrium if q = -Q/4.
20. Two point charges 3µC and
-3µC are located 20cm apart in vacuum. Find electric field and electric
potential at midpoint of line. Also find force and its direction experienced by charge
1.5nC kept at
midpoint.
21. A 10µF capacitor
is charged by a 30V d.c. and then connected across an uncharged 50µF capacitor.
Calculate (i) the final potential difference of the combination, and (ii) the initial
and final energies. How will you account for the difference in energy?
22. An electric dipole of length 4cm, when placed with its axis
making an angle of 60o with uniform
electric field experiences a torque of 4 /3Nm. Calculate the (i) magnitude
of electric field, (ii)the
potential energy of dipole ,if the dipole has charges of +8nC.
