13.1 QUESTIONS
1. What
is it in an atomic structure which differentiates between inert gases and some
metals? Name some examples.
2. What
charge does an electron carry?
3. How
do you explain an electric current in electron terms? What is its direction?
4. What
is the difference between a primary and a secondary cell?
5. Describe
the elements of a ‘dry’ battery.
6. What
are the main differences between lead-acid and alkaline secondary cells? What are the advantages of alkaline cells?
7. Why
must a lead-acid cell never be left in a discharged state?
8. Why
must battery rooms be ventilated?
9. About
what specific gravity reading would you expect a fully charged lead-acid cell
to show?
10. Approximately
how much of the charge energy of a battery would you expect to recover in use?
11. A
battery is rated 250Ah at the 5-hour rate.
For how long could you draw 7A from it continuously? If you drew 70A continuously, what effect
would you expect on the battery’s performance?
12. What
effect would the discharging of a nickel-cadmium cell have on the electrolyte’s
specific gravity?
13. What
is the difference between natural magnetism and electromagnetism? Sketch an electromagnetic coil, illustrating
the field direction.
14. Name
some uses for an electromagnet.
15. What
is the equivalent resistance of several resistors in series?
16. What
is the equivalent resistance of several resistors in parallel?
17. Write
down Ohm’s Law in its three variations, naming the units used.
18. What
is the rate of heat production when current flows in a conductor of known
resistance? How can the heat rate be
reduced?
19. What
is understood by Faraday’s ‘Law of Electromagnetic Induction’? Illustrate your answer by a sketch.
20. How
do you use Fleming’s Right-hand Rule for generated emf?
21. What
force acts on a conductor carrying current in a magnetic field? Illustrate your answer with a sketch.
22. Why
does the current rise slowly when a voltage is applied to an inductive
circuit? What do you understand by
‘back-emf’, and what is it proportional to?
23. For
an inductor of inductance L henrys,
write down the formula connecting L, the
back-emf E and the rate of change of
current.
24. In
the inductor of Q.23, if the current flowing at any instant is I, what is the energy stored in the
inductor? In what unit?
25. What
do you understand by the ‘time constant’ of an inductive (R-L) circuit?
26. What happens if you suddenly switch off
an inductive circuit? How can any
ill-effects be mitigated?
27. In
what unit is capacitance now measured?
Is it a practical unit?
28. What do you understand by the
‘dielectric’ of a capacitor? How does it
function?
29. A
capacitor of capacitance C is charged
to a voltage V. What is the energy stored in it? In what unit?
30. Describe
an electrolytic capacitor. How does it
compare with a normal type?
31. Why
must an electrolytic capacitor never be reverse-charged? How is this to be avoided?
32. What
is the equivalent capacitance of a number of capacitors in series?
33. What
is the equivalent capacitance of a number of capacitors in parallel?
34. What
is the time constant of a capacitive (R-C) circuit?
35. How
is a capacitor/resistor combination used to provide a time delay to an
operating circuit? Make a sketch.
36. What
is the power transmitted in a d.c. circuit by a current of / amperes at a
pressure of V volts? If the resistance of the circuit is R ohms, express this power in two alternative
forms. What is the unit of the power?
37. What
is the equivalent in kWm of 20 horsepower?
38. What
is the efficiency of a motor with full-load output of 50 hp and an electrical
input of 45kW?
39. Name any three classes of d.c.
measuring instrument, indicating their principal features and differences.
40. How
can you tell a moving-iron from a moving-coil instrument simply by looking at
it?
41. What
difference is there between the movements of a moving-iron ammeter and a
moving-iron voltmeter?
42. How
does a dynamometer instrument operate as a wattmeter? Can it indicate reverse
power flow?
43. What
is a ‘set-up zero’ instrument, and when is this feature used?
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