QUESTION PAPER 8

Note: Attempt any five questions from the following (5 × 14 = 70 Marks)
1. a) Two similar coils each of resistance 50 ohms are connected in series across a supply of
200 volts. What resistance must be connected across one of the coils to reduce the
voltage across it to 80 volts? (7)
b) A parallel plate capacitor has composite dielectric media consisting of relative
permittivity’s 3, 4 and 5 with thickness 0.5 mm, 0.6 mm and 0.8 mm respectively.
The plates are 2 mm apart and each of cross section area 1000 cm2;find the
capacitance of the parallel plate capacitor. (7)
2. a) What is meant by static electricity and how it is generated? (7)
b) Why it is important to bond and ground containers? (7)
3. a) Compare magnetic and electric circuits. (7)
b) Two identical coils A and B each having 1000 turns lie in parallel planes such that
60% of the flux produced by one coil links with the other. A current of 12 A in coils A
produces in it a flux of 10-4 weber. If the current in coil A is revered in 0.02 seconds,
what would be the magnitude of the emf induced in coil B? (7)
4. a) With neat sketch explain the working principle of transformer. (7)
b) Calculate the magneto motive force required to establish a flux density of
1.3Wb/m 2 in the 2 mm air gap of an electromagnet having an iron path of 2 meters.
Take the relative permeability of the iron as 1500. Neglect leakage flux. (7)
5. a) Explain the working principle of D.C. generator. Can a D.C. generator be converted
into an A.C. generator? (6+1)
b) An 8 – pole D.C. generator has 650 armature conductors. The flux per pole is 20
mWb. Find the value of emf generated when the armature is wave wound and is
rotating at a speed of 1200 RPM. What must be the speed at which the armature is to
be driven to generate the same emf, if the armature is lap wound? (7)
6. a) What do you mean by “Heating effect of Electric Current”? What are all the
applications of it? (3+4)
b) Differentiate between series, shunt and compound D.C. motor. (7)
7. a) What is magnetic compass? Explain dry compass and wet card compass. (10)
b) Discuss earth as magnet. (4)
8. a) A voltage of 200 V is applied to a series circuit consisting of resistor, inductor and
capacitor. The voltages across them are 170 V, 150 V and 100 V respectively. Find
the power factor of the circuit. When a current of 4 A flows through them. (7)
b) With help of hysteresis loop compare soft and hard magnetic material. (7)
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