If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

# Question 2cd: 2015 AP Physics 1 free response

Testing if a bulb is nonohmic.

## Want to join the conversation?

• Sal, I might be wrong, but I think the AP graders would count changing the power source as modifying the system. Thanks for the video!
(1 vote)
• The FRQ grading rubric for this question wasn't very specific about this, but from the example they gave, it sounds like they only want modifications that would change the structure. Since the power source was already there, they wouldn't truly consider that a modification. I'm not certain though...
(1 vote)
• At , how could Sal use Ohm's Law to determine if the bulb is nonohmic? Isn't it a paradox?
(1 vote)
• You can use Ohms law at any point to find a value. Its just that you cant have the same resistance at multiple voltages/currents if its non ohmic.
(1 vote)
• Would it be worth mentioning that setting the power source to a high voltage would help to decrease the percent error of the ammeter and voltmeter (because the difference from actual value will be less significant), or is mentioning rounding enough?
(1 vote)
• Can't you just make a V-I graph to determine whether it is non-ohmic?
(1 vote)
• That would be a way. You need to get the V-I data, of course.
(1 vote)
• How did Sal determine the sig figs of the ohmeter and ammeter to 0.1 ohms and 0.01 amps in part d of the problem ?