A 9 V supply is connected to a resistor. If the resistance increases from 2 Ω to 3 Ω, what happens to the current?

• A. The current increases from 4.5 A to 6.75 A
• B. The current stays the same
• C. The current falls from 4.5 A to 3 A
• D. The current falls to 0 A

Answer: (C)

With a fixed voltage, current goes down when resistance goes up because I = V/R. The 9 V source gives an initial current of 9/2 = 4.5 A. If the resistance increases to 3 Ω, the current becomes 9/3 = 3 A. Therefore the current falls from 4.5 A to 3 A. The higher resistance reduces the flow of charges, so the current cannot stay the same, rise, or drop to zero in this scenario.