# Solve Battery Problem: Calculate Resistance & Power Increase

• mer584
In summary, the conversation discusses the calculations for the resistance and power of a flashlight that uses two D-cell batteries connected in series. It also addresses the potential increase in power if four D-cell batteries were used with the same bulb. The correct answer is four times the original power, as doubling the voltage in a series circuit quadruples the power.
mer584

## Homework Statement

An Ordinary flashlight uses two D-cell 1.5V batteries connected in series. The bulb draws 450mA when turned on. A)Calculate the resistance of the bulb and the power dissipated. B) By what factor would the power increase if 4 D-cell batteries in series were used with the same bulb? (neglect heating effects)

2. Homework Equations
P=IV=I^2R=V^2/R V=IR

3. The Attempt at a Solution
I understand part A, and I got 1.4W for the power. For part B though, I keep getting that it's 2 times greater by doing P=IV where (.45A)(4 x 1.5) =2.7. but I know the answer is supposed to be 4 times. I'm pretty sure the current stays constant and that you add voltages, so I'm confused why it would be 4 and not 2.

You should post these questions either in introductory physics or in the engineering homework help subforum.

I get P = 1.35 W for part a), and 5.4 W for part b)

Doubling the voltage doubles the current, which quadruples the power.

EDIT: Your mistake is that you used the original current in your calculation for part b), rather than using the new current once having calculated it.

Last edited:
Thank you. I did post this in the introductory forum about 3 hours ago but no one was able to respond so I thought maybe I needed to put it here, figuring someone would be able to answer it quickly--which fortunately was the case. Sorry to take your time.

## 1. How do I calculate the resistance of a battery?

To calculate the resistance of a battery, you will need to know the voltage and current of the battery. Then, you can use the formula R = V/I, where R is the resistance, V is the voltage, and I is the current. You may also need to take into account any internal resistance of the battery.

## 2. What is the relationship between resistance and power in a battery?

The relationship between resistance and power in a battery is inversely proportional. This means that as the resistance increases, the power output decreases. This is because a higher resistance causes more energy to be converted into heat rather than being used to power devices.

## 3. How can I increase the power output of a battery?

To increase the power output of a battery, you can decrease the resistance by using thicker wires or connecting multiple batteries in parallel. You can also increase the voltage of the battery, which will also increase the power output. However, be cautious not to exceed the recommended voltage for your devices.

## 4. Why is it important to calculate the resistance and power of a battery?

Calculating the resistance and power of a battery is important because it allows you to determine the battery's capabilities and how it will perform in different circuits. It also helps you to ensure that the battery is not being overloaded, which can cause damage or reduce its lifespan.

## 5. Can I use the same formula to calculate resistance and power for all batteries?

The formula R = V/I can be used to calculate resistance for all batteries. However, the power output may vary depending on the type, size, and condition of the battery. It is best to consult the manufacturer's specifications for the specific battery you are using to get an accurate calculation of power.

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