What would be the voltage drop across the series resistor of the circuit shown in figure "B" of the illustration if the source is 30 volts, the resistance of R1 is 10 ohms, R2 is 10 ohms and R3 is 10 ohms? See illustration EL-0032.
• Series vs. parallel resistors in figure B (which resistor is in series with the source?) • Equivalent resistance of two equal resistors in parallel (R1 and R2) • Using Ohm’s law ( V = I \times R ) to find voltage drop once circuit current is known
• First, look at figure B and decide which resistor is the only one that all current must flow through before it splits. • Next, find the combined (equivalent) resistance of R1 and R2 in parallel, then add that to the series resistor to get total circuit resistance. • Once you know the total resistance and the source voltage, what is the circuit current, and how much voltage will be dropped across the series resistor alone?
• Be sure you have correctly identified R3 as the series resistor in figure B, and R1 and R2 as parallel. • Verify the equivalent resistance of two 10‑ohm resistors in parallel before moving on. • Before choosing an answer, check that the sum of all individual voltage drops equals the 30‑volt source (Kirchhoff’s Voltage Law).
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