# Calculating Resistance of a Light Bulb

• Kryttle
In summary, the task is to hook up a round bulb to two D batteries and measure the voltage drop and current through the bulb. The equation R=deltaV/I can be used to calculate the resistance of the bulb, with the voltage drop (2.25v) and current (0.24A) measured as inputs. The voltage (V) in the equation refers to the number given by the multimeter for the voltage drop across the 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

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.

Welcome to PF!

Hi Kryttle! Welcome to PF!
Kryttle said:
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.

Last edited by a moderator:

## 1. How do you calculate the resistance of a light bulb?

To calculate the resistance of a light bulb, you will need to know the voltage and current values. Then, use Ohm's law (R = V/I) to calculate the resistance. The voltage can be measured with a voltmeter and the current can be measured with an ammeter.

## 2. What is the unit of measurement for resistance?

The unit of measurement for resistance is ohms (Ω). This is named after the German physicist Georg Ohm, who discovered the relationship between voltage, current, and resistance.

## 3. How does the temperature of a light bulb affect its resistance?

The temperature of a light bulb can affect its resistance. As the temperature increases, the atoms in the filament vibrate more, causing more collisions and increasing the resistance. This is known as the temperature coefficient of resistance.

## 4. Can the resistance of a light bulb change over time?

Yes, the resistance of a light bulb can change over time. As the filament heats up and cools down with use, it can become more brittle and its resistance can increase. This is why light bulbs eventually burn out.

## 5. How can I use the resistance of a light bulb to determine its wattage?

To determine the wattage of a light bulb, you can use the formula P = V^2/R, where P is power in watts, V is voltage, and R is resistance. By measuring the voltage and resistance of a light bulb, you can calculate its wattage and determine how much energy it consumes.

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