DC ELECTRIC CIRCUITS - Day 3

Question 1: EE Board March 1998

     Three resistors of 10, 15 and 20 ohms each are connected in parallel. What is the equivalent resistance?

A. 45 ohms

B. 17.2 ohms

C. 0.22 ohm

D. 4.62 ohms

Question 2:

   The equivalent resistance of three resistors A, B and C connected in parallel is 1.714 ohms. If A is twice of B and C is half as much as B, find the equivalent resistance when the three of them are connected in series.

A. 17.5 ohms

B. 21.0 ohms

C. 24.5 ohms

D. 28.0 ohms

Question 3:

     Three resistors of 10, 12 and 15 ohms are connected in parallel. Evaluate the value of current to the parallel system that will make the current in the 10 ohm resistor equal to 2 A.

A. 5 A

B. 6 A

C. 4 A

D. None of these

Question 4:

     Three resistors of 10, 12 and “x” ohms, respectively are connected in parallel across a constant current source of 8 A. Determine “x” if this resistor draws

2.5 A.

A. 10Ω

B. 12Ω

C. 13Ω

D. 11Ω

Question 5:

     Two resistors A and B made of different materials have temperature coefficients of resistance at 20 ⁰C of 0.004 and 0.006 respectively. When connected across a voltage source at 20 ⁰C, they draw current equally. What percentage of the total current at 100 ⁰C does resistor A carry?

A. 47.14%

B. 52.86%

C. 61.34%

D. 38.66%

Question 6:

Two resistor A and B made of different materials have temperature coefficients of resistance of 0.003 and 0.005, respectively. When connected in parallel across a voltage source at 15 ⁰C, it consumes equal power. What is the ratio of the power drawn by resistor B to that in resistor A when temperature rises to 60 ⁰ C? Assume supply voltage is constant.

A. 0.829

B. 0.926

C. 0.964

D. 0.882

Question 7: EE Board March 1998

Three resistor of 10, 15 and 20 ohms each are connected in parallel. What is the total conductance?

A. 0.217 mho

B. 3.41 mhos

C. 4.62 mhos

D. 0.52 mho

Question 8:

     Two heating units x and y are connected across a 100 V supply. Unit y takes twice as much power as unit x. Total power supplied by the source is 2280 watts. Determine the total power drawn by the heating units if they are connected in series across the same source.

A. 615.32 W

B. 506.58 W

C. 582.45 W

D. 604.38 W

Question 9:

     Three resistors R , R  and R  are connected in series-parallel with R1 in series with the parallel combination of R2 and R3. The whole combination is connected across a 120 V DC source. Resistors R1, R2 and R3 take 750 W, 250 W and 200 W, respectively Calculate the resistance R2.

A. 8.10Ω

B. 8.52Ω

C. 7.84Ω

D. 9.22Ω

Question 10:

Two lamps X and Y are connected in series. Lamp X is rated 50 W at 100 V while lamp Y is rated at 100 W at 100 V also. The two lamps are to be connected in series across a 200 V source. What resistance must be connected across lamp A so that each lamp will operate properly?

A. 150 ohms

B. 100 ohms

C. 200 ohms

D. 180 ohms