For the circuit shown in diagram below, note that the voltage between points a a

Question

For the circuit shown in diagram below, note that the voltage between points a and c is 12V. Voltage measured across a battery is always the battery voltage. In practice, a significant draw on the battery can overload it and reduce its driving force, but we'll ignore that detail for now. What is the total current in the circuit? What is the voltage between points a and b? Hint: The voltage measured across a resistor, known as the voltage drop, is given by Ohm's law. What is the voltage between points b and c? What is the sum of the voltage drops across the two resistors? How does this compare with the battery voltage?

Explanation / Answer

Current I is related to voltage and resistance through: I = V/R

In this case both the resistors are in series, So: R = 3 + 9 = 12 ohms

a) Hence current in the circuit = V/R = 12/12 = 1A

b) Voltage drop across a resistor = I * R_resistor. Bwetween a and b resistance = 3ohms, so V_drop = 1 x 3 = 3V

c)Similary, between b and c resistance = 9ohms, So, V_drop = 1 x 9 = 9V

d) Total voltage drop across the resistors = 3V + 9V = 12V

This is equal to the total battery voltage

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