Element 3F Question 132

Question:

[EL3F-132]  (Refer to figure EL3F2)  What is the voltage drop across R1?
 
a) 9 volts.
b) 7 volts.
c) 5 volts. [Correct Answer]
d) 3 volts.

Challenger's excerpt:

Look at Figure EL3-F2 and notice that the diode is reversed biased, and will look like an open circuit to this series circuit problem. Current will be the same throughout all of the series circuit, and the sum of the voltage drops across the individual components will equal the source voltage (Kirchoffs Law).

Total Resistance is equal to: R1 + R2 + R3 = RT

The current is equal to the voltage source divided by the total resistance.

10 Volts / 600 Ohms = 16.6mA

If you calculate the 100 Ohm resistor the voltage works out to be 1.666 Volts.

100 Ohms X .016 Amps = 1.666 Volts

If you calculate the 200 Ohm resistor the voltage works out to be 3.333 Volts.

200 Ohms X .016 Amps = 3.333 Volts

If you calculate the 300 Ohm resistor the voltage works out to be 4.999 Volts.

300 Ohms X .016 Amps = 4.999 Volts

The answer to 3F132 is (C) which is 5 Volts. R1 can only be the 300 Ohm resistor because that is the only resistor that drops 5 Volts.

Response:

Your analysis is correct.

Recommendation:

Change the diagram to reflect R1 as a 300 W resistor and R3 as a 100 W resistor as illustrated below so it correlates with the question.

[EL3F-132]  (Refer to figure EL3F2)  What is the voltage drop across R1?
 
a) 9 volts.
b) 7 volts.
c) 5 volts. [Correct Answer]
d) 3 volts.