Calculating Resistance of a Light Bulb

[Kryttle]

Homework Statement

Hook up a round bulb to two D batteries. Measure the voltage drop across the bulb. Measure the current flowing through the bulb. Calculate the resistance of the bulb. V=2.25v; I=0.24A

Homework Equations

R=deltaV/I

The Attempt at a Solution

Is the "V" in the equation the number the multimeter gave me (2.25v) or do I use 3.0v-2.25v=0.75? In the first case R=9.3. Using 0.75v R=3.13.

 

[tiny-tim]

Welcome to PF!

Hi Kryttle! Welcome to PF!

Measure the voltage drop across the bulb.
…
Is the "V" in the equation the number the multimeter gave me (2.25v) …

Yes.

In V = IR (Ohm's Law), the https://www.physicsforums.com/library.php?do=view_item&itemid=301" drop and the resistance are both measured across the (same) component.