What would be the voltage drop across the series string of the circuit shown in figure "A" of the illustration if the source voltage is 30 volts, the resistance for R1 is 10 ohms, the resistance for R2 is 10 ohms and the resistance for R3 is 10 ohms? Illustration EL-0032
• In a series circuit, the same current flows through each resistor and the sum of all individual voltage drops equals the source voltage. • Use Ohm's Law (V = I \times R) and the idea of equivalent resistance: add all series resistances together first. • Compare the total voltage across R1 + R2 + R3 with the source voltage in a closed circuit like figure A.
• First, compute the total resistance of R1, R2, and R3 in series. What is that value with each at 10 ohms? • Using the source voltage of 30 volts and your total resistance, determine the circuit current with Ohm's Law. • Once you know the current, what must the total voltage drop across the entire resistor string (R1 + R2 + R3 together) be in relation to the 30‑volt source?
• Be sure you are finding the drop across the whole series string (R1 + R2 + R3 together), not just a single resistor. • Verify that you have correctly added the series resistances: R_total = R1 + R2 + R3. • Double‑check your final value against the rule that in a DC series circuit, the sum of all voltage drops must equal the source voltage.
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