Stu wanted to calculate the resistance of a light bulb
connected to a 4.0-V battery, with a resulting current of
0.5 A. He used the formula R = VI and obtained an
answer of 2 . Was Stu's answer correct? How do you
know?

8 ohms

Explanation:

Using ohms law,

V = IR

Or

R = V/I

Where

V = voltage

I = current

R = resistance

Given

V = 4.0V

I = 0.5 A

Therefore

4.0 = 0.5 x R

Divide both sides by 0.5

4.0/0.5 = 0.5/0.5 x R

8 = R

R = 8 ohms

He’s wrong because he used the wrong formula . If he used R = V/I , he’d have gotten it correctly