In a series circuit with a 30-volt supply and resistors of 10 ohms and 20 ohms in series, what is the voltage drop across the 10-ohm resistor?

In a series circuit with a 30-volt supply and resistors of 10 ohms and 20 ohms in series, what is the voltage drop across the 10-ohm resistor?

• A. 10 volts
• B. 12 volts
• C. 20 volts
• D. 30 volts

Answer: (A)

In a series circuit, the same current flows through every component and the total supply voltage is shared among the resistors in proportion to their resistances. Add the resistances: 10 Ω + 20 Ω = 30 Ω. The current is the supply voltage divided by total resistance: I = 30 V / 30 Ω = 1 A. The voltage drop across a resistor is V = I × R, so across the 10 Ω resistor: V = 1 A × 10 Ω = 10 V. The 20 Ω resistor then drops the remaining 20 V (1 A × 20 Ω), adding up to the total 30 V. So the voltage drop across the 10-ohm resistor is 10 volts.

In a series circuit, the same current flows through every component and the total supply voltage is shared among the resistors in proportion to their resistances. Add the resistances: 10 Ω + 20 Ω = 30 Ω. The current is the supply voltage divided by total resistance: I = 30 V / 30 Ω = 1 A. The voltage drop across a resistor is V = I × R, so across the 10 Ω resistor: V = 1 A × 10 Ω = 10 V. The 20 Ω resistor then drops the remaining 20 V (1 A × 20 Ω), adding up to the total 30 V. So the voltage drop across the 10-ohm resistor is 10 volts.