Page 95 - Basic Electrical Engineering

31. Two adjacent conductors are carrying current in the opposite directions. Show that there will
be force of repulsion between the conductors.
32. When capacitors are connected in parallel, their equivalent capacitance is increased. Explain
why?
33. Explain why capacitors are called energy storage devices.
34. What is the meaning of relative permittivity or dielectric constant? What is it’s unit?
35. Write three formulae of electrical power.
6
36. Prove that 1 kWh is equal to 3.6 × 10 Joules.
37. The most important property of a capacitor is its ability to block steady dc voltage while
passing ac signals, explain.
38. Define the Farad unit of capacitance.
39. How is energy stored in a capacitor? On what factors does it depend?
40. What are the physical factors that affect the capacitance of a capacitor?
41. Two coils of N = 50 and N = 500 turns, respectively, are wound side by side on an iron ring
1
2
2
of cross-sectional area of 50 cm and mean length of 120 cm. Calculate the mutual inductance
between the coils, self inductance of the coils, and the coefficient of coupling assuming
permeability of iron as 1000.

[Ans 0.13 H, 0.013 H, 1.3 H, 1.0]

42. Two coils of N = 1500 and N = 200 turns are wound on a common magnetic circuit of
2
1
4
reluctance 25 × 10 AT/Wb. Calculate the mutual inductance between the coils.

[Ans 1.2 H]

43. Two coils have a mutual inductance of 400 μH. Calculate the EMF induced in one coil when
current in the second coil varies at a rate of 6000 Amperes per second.

[Ans 2.4 V]

44. Two similar coils have a coupling coefficient of 0.4. When the coils are connected in series
cumulatively, the total inductance becomes equal to 140 mH. Calculate the self-inductance of
each coil.

[Ans 50 mH]

45. Two coils when connected in series cumulatatively show to have a total inductance of 2.4 H
and when connected in series but differentially show a total inductance of 0.4 H. The
inductance of one coil when isolated is calculated as equal to 0.8 H. Calculate (a) the mutual
inductance and (b) the coefficient of coupling between the coils.