Question T5D06
From subelement T5 - T5D
What is the resistance of a circuit that draws 4 amperes from a 12-volt source?
Why is this correct?
The correct answer is A (3 ohms). Using Ohm's Law, resistance equals voltage divided by current: R = E / I = 12 volts / 4 amperes = 3 ohms. Choice B (16 ohms) incorrectly multiplies voltage and current. Choice C (48 ohms) also multiplies instead of dividing. Choice D (8 ohms) uses the wrong current value in the calculation.
Memory tip
When finding resistance, always divide voltage by current. The word 'draws' indicates current flow from the source. Remember: higher current through the same voltage means lower resistance, since resistance opposes current flow.
Learn more
In practical amateur radio circuits, understanding resistance calculations helps determine proper component ratings and power dissipation. When designing antenna tuners or impedance matching networks, you'll frequently calculate circuit resistance to ensure components can handle the current flow. Lower resistance values allow higher current flow at the same voltage, which affects heat generation and component selection in RF applications.
Think about it
Why do you think a circuit with lower resistance would draw more current from the same voltage source?