Question

If the cross-section of a wire of fixed length is doubled, how does the resistance of that wire change? (this is for studying for my semester exam. I got the question wrong on one of my chapter tests so I'm trying to find out what the correct answer was)

A. Halved
B. Doubled (I know it's NOT this cause that was the wrong one)
C. Unchanged
D. Quadrupled

Answer 1

Apart from using the right formula (there's one that relates the resistance of a wire to its length and cross-section), you could try an analogy. For currents and resistors, compraing the situation with water flows usually works.

What would the equivalent of resistance be in a flowing river? And what would happen when the river suddenly becomes wider?

Answer 2

Would that make it halved?

Answer 3

Yes it would.

A wider river/wire would allow the current to flow easier (and thus with less resistance).

The formula I mentioned is \[R = \rho\frac{l}{A}\] (see e.g. http://www.physicsclassroom.com/class/circuits/u9l3b.cfm )

Answer 4

Yay!!! Thank you!!!

Answer 5

No problem!