Calculating Energy Delivered to a Battery using Ohm's Law

[tigerguy]

A battery charger is connected to a dead battery and delivers a current of 7.5 A for 3.5 hours, keeping the voltage across the battery terminals at 12 V in the process. How much energy is delivered to the battery?

I'm not exactly sure what I am doing wrong. I understand that we have to use Ohm's Law in this question. So doing that, I took the given current, and converted it into the total number of coloumbs used over the 3.5 hours. I then calculated the resistance, and then I multiplied the total coloumbs by the resistance, and got joules (151,200). That's wrong, so I'm not sure where I went wrong.

I'd appreciate any help. Thanks.

 

[sdekivit]

A battery charger is connected to a dead battery and delivers a current of 7.5 A for 3.5 hours, keeping the voltage across the battery terminals at 12 V in the process. How much energy is delivered to the battery?

I'm not exactly sure what I am doing wrong. I understand that we have to use Ohm's Law in this question. So doing that, I took the given current, and converted it into the total number of coloumbs used over the 3.5 hours. I then calculated the resistance, and then I multiplied the total coloumbs by the resistance, and got joules (151,200). That's wrong, so I'm not sure where I went wrong.

I'd appreciate any help. Thanks.

use $$E = P \cdot t = U \cdot I \cdot t$$ with t in seconds.

 

[kyle8921]

Hello, thank you for reaching out for help with this question. It seems like you have a good understanding of Ohm's Law and how to calculate the energy delivered to a battery. However, there are a few things to consider in this specific scenario.

First, it is important to note that the voltage across the battery terminals will not remain constant at 12 V throughout the entire charging process. As the battery charges, the voltage will increase, and the current will decrease. This means that the resistance will also change over time.

Secondly, when using Ohm's Law to calculate the energy delivered to a battery, you need to use the voltage and current at the specific moment in time that you are interested in, not the average values over the entire charging period. So in this case, you would need to use the voltage and current at the end of the 3.5 hours to calculate the energy delivered.

Lastly, make sure you are using the correct units in your calculations. The unit for resistance is ohms, and the unit for current is amperes, or amps. Make sure you are converting your units correctly to get the final answer in joules.

I hope this helps clarify where you may have gone wrong in your calculations. If you have any further questions, please don't hesitate to ask. Good luck!