Deck 8: Transients, D.C Circuit Analysis, and D.C Machines

Question 1

Decide whether each of these statements is True (T) or False
When a capacitor of 8μF, which has been charged to 12 V, is connected across a 1 MΩ resistor:
(i) The circuit current is proportional to the rate of change of voltage across the capacitor.
(ii) 8 s after the connection, the circuit current has dropped to half its initial value.

A) (i) T (ii) T
B) (i) T (ii) F
C) (i) F (ii) T
D) (i) F (ii) F

Answer 1

B

Question 2

Decide whether each of these statements is True (T) or False
A 24 V supply is connected to a series arrangement of a 100 Ω resistor and a 50 mH inductor.
(i) The initial circuit current is 0.24 A.
(ii) After a time equal to the time constant, the circuit current has decreased to 36.8% of its initial value.

A) (i) T (ii) T
B) (i) T (ii) F
C) (i) F (ii) T
D) (i) F (ii) F

Answer 2

A

Question 3

Decide whether each of these statements is True (T) or False
For a series wound d.c. motor:
(i) The armature and field coils always carry the same current.
(ii) The motor has a high starting torque.

A) (i) T (ii) T
B) (i) T (ii) F
C) (i) F (ii) T
D) (i) F (ii) F

Answer 3

A

Question 4

Decide whether each of these statements is True (T) or False
For a shunt wound d.c. motor:
(i) The armature and field coils always carry the same current.
(ii) The motor has a high starting torque.

A) (i) T (ii) T
B) (i) T (ii) F
C) (i) F (ii) T
D) (i) F (ii) F

Question 5

Decide whether each of these statements is True (T) or False
With a d.c. generator, a split-ring commutator is used to:
(i) Reverse the connections to the rotor winding every half-cycle.
(ii) Via brushes give the output voltage.

A) (i) T (ii) T
B) (i) T (ii) F
C) (i) F (ii) T
D) (i) F (ii) F

Question 6

The Thévenin equivalent circuit for the circuit to the left of the terminals X and Y in the following circuit is:

A) A voltage source of 4 V with series resistance 25Ω
B) A voltage source of 4 V with series resistance 8Ω
C) A voltage source of 5 V with series resistance 25Ω
D) A voltage source of 5 V with series resistance 8Ω