Question T5D03
From subelement T5 - T5D
What formula is used to calculate resistance in a circuit?
Why is this correct?
The correct formula R = E / I comes from rearranging Ohm's Law (E = I × R). To isolate resistance, divide both sides by current: R = E / I. This means resistance equals voltage divided by current. Option A (R = E × I) would give units of volt-amperes, not ohms. Options C and D (addition/subtraction) are mathematically incorrect since electrical relationships follow multiplicative/divisive patterns, not additive ones.
Memory tip
Remember the algebraic manipulation: when a variable is multiplied in the original equation (E = I × R), you divide to isolate it (R = E / I). This same pattern applies to finding current: I = E / R. The division relationship reflects that higher voltage drives more current through the same resistance.
Learn more
In practical circuits, this formula helps determine if components can handle expected loads. A 12V circuit drawing 4A has 3-ohm resistance (12÷4=3). If you need higher resistance to reduce current flow, you'd add series resistance. Lower resistance increases current, which is why transmission line impedance matching matters for efficient power transfer in amateur radio systems.
Think about it
Why do you think resistance calculations use division rather than multiplication, and what would happen to circuit behavior if the mathematical relationship were different?