Question T5D04
From subelement T5 - T5D
What is the resistance of a circuit in which a current of 3 amperes flows when connected to 90 volts?
Why is this correct?
The correct answer is B (30 ohms) because resistance is calculated using R = E / I. With 90 volts and 3 amperes: R = 90V ÷ 3A = 30 ohms. Choice A (3 ohms) incorrectly uses just the current value. Choice C (93 ohms) incorrectly adds voltage and current. Choice D (270 ohms) incorrectly multiplies voltage and current, which would give power, not resistance.
Memory tip
For Ohm's Law problems, identify what you're solving for first, then select the matching formula. When calculating resistance, you always divide voltage by current (R = E/I). The units help verify: volts ÷ amperes = ohms.
Learn more
Understanding resistance calculation is crucial for station design and troubleshooting. When designing antenna systems or selecting appropriate resistors for circuits, you'll frequently need to determine resistance values based on operating voltage and expected current draw. Higher resistance means lower current for the same voltage, which affects power consumption and component heating. This relationship becomes especially important when calculating transmission line characteristics and impedance matching in RF circuits.
Think about it
Why do you think the incorrect answers represent common mathematical mistakes students make when first learning Ohm's Law formulas?