Introduction to Electric Circuits

62 DC circuit analysis

9 Three resistors each of 12 ~ resistance are connected in delta. Determine

the resistance of each of the equivalent star connected resistors.

10 Three resistors each of 10 lq resistance are connected in star. Calculate the

resistance of each of the equivalent delta connected resistors.

11 A voltage source has an internal resistance of 100 lq and an open circuit

terminal voltage of Vs. Determine the resistance of the load resistor if:

(a) the power transferred to the load is to be a maximum;

(b) the required load voltage is 0.9 Vs.

12 A voltage source Vs having a resistance Rs supplies a load RL via a
transmission line of resistance RT. If the power transferred to the load is to
be maximized specify:
(a) RL if Rs = 100 12 and RT = 10 f~
(b) Rx if RL = 10 1~ and Rs = 5
(c) Rs if RL = 40 f~ and RT = 10 II

3.12 PROBLEMS

1 Use (a) Kirchhoff's laws and (b) Thevenin's theorem to determine the

current through the 10 f~ resistor in the circuit of Fig. 3.40.

5f~ 15f2

1 I I I

C

Figure 3.40

)100V [~ 20f~ l-~ 10~

3~ 17f~

l I! I

2 Calculate the current in the 1 lq resistor in the circuit of Fig. 3.41 using (a)

the principle of superposition and (b) Thevenin's theorem.

2f~ 3~

-----I F! I

C ,ov I ,o C

5v

Figure 3.41

3 Determine the Thevenin equivalent circuit between the terminals A and B

in the circuit of Fig. 3.42.