Physics help needed regarding POWER?

Question

Hi I had some questions? Could you help me
I am in the 7th grade and I do not understand. I will pick the best answer right away! Bye

On my powerbill the total kWh used this month is 222,
Days: 27, Avg KWh per Day is 8, & Avg Cost per Day is $0.87.
I needed some help doing some analysis.

To the nearest tenth of a cent, how much does 1 kWh cost?
-is that 0.087 cent?

I was trying to figure out in joules how energy i consume? Is there a formula and how do I do that?
-From my own research the answer I got was 799,200,000 J

Next, I wanted to find the average power consumption in Watts? (I am not sure what formula to use or how to go about this?

Also, the power company has noted that I am provided with 120 V? Based on the power consumption, what is the average current running in my house?

And in general, I was wondering how much would it cost me to leave all the lights on in the house for one day. I have 70 bulbs in my house that are all 75 watts?

Thanks!

Answer 1

You used 222 kWh over 27 days with an average kWh usage of 8 kWh per day. Your cost per day is $0.87

If you use 8 kWh per day, and your cost is $0.87 per day, then the cost per kWh is: $0.87 / day ÷ 8 kWh / day = $0.10875 per kWh. 10.875¢ per kWh.

Energy can be expressed in the following units:
kWh, Joules, Calorie, Newton-meter

1 kWh = 3,600,000 Joules. The reason for the large conversion factor is because you’ve got kilowatts, (1000 watts) and hours (3600 seconds)

222 kWh x 3,600,000 Joules / kWh = 799,200,000 Joules

Your average power consumption is your average usage over 27 days. You need to convert this to hours. 27 days x 24 hours / day = 648 hours.

Your average power consumption is 222 kWh / 648 h = 0.342 kW or 342 watts.

You could have also computed this as 8 kWh / 24 h = 0.333 kW. The slight difference is due to the utility rounding the daily usage values.

I will use 342 watts for the remaining calculations:

Note: There is a concept called power factor that applies to AC power consumption, however this is beyond the scope of 7th grade science class. We will assume unity power factor for the remaining calculations.

Voltage x Current = Power
volts x amps = watts

We know watts and volts, so we use algebra to solve for amps.
amps = watts / volts
342 watts / 120 volts = 2.85 amps

70 light bulbs x 75 watts / bulb = 5250 watts or 5.25 kW
Burning for 24 hours: 5.25 kW x 24 hours = 126 kWh.

At your energy cost of $0.10875 per kWh:
126 kWh x $0.10875 = $13.70 per day

Answer 2

This is a 7th grade problem??? Wow.

Well, I'm not going to do your HW for you but you can get started with a little information. Like 87 cents per day divided by the 8 kWh per day gives you 10.9 cents per kWh. Which is really pretty reasonable.

A kWh is 3.6 million joules. So, you can go from there.

Finally, 120 V is the US standard, and P = VI, where I is the current. So, how about using average P / V?

You can use that information (above) to answer the rest of your questions.

Answer 3

Are you kidding? On my powerbill the total kWh used this month is 222, Days: 27, Avg KWh per Day is 8, & Avg Cost per Day is $0.87. I needed some help doing some analysis. To the nearest tenth of a cent, how much does 1 kWh cost? -is that 0.087 cent? 10.1 Cent I was trying to figure out in joules how energy i consume? Is there a formula and how do I do that? -From my own research the answer I got was 799,200,000 J Next, I wanted to find the average power consumption in Watts? (I am not sure what formula to use or how to go about this? 1 KW = 1,000 Watts Also, the power company has noted that I am provided with 120 V? Based on the power consumption, what is the average current running in my house? Current = Watts/Volts But power does not flow evenly for 24 hours, but depending on load (Items switched on at any given time) And in general, I was wondering how much would it cost me to leave all the lights on in the house for one day. I have 70 bulbs in my house that are all 75 watts? 24*70*75/1000*.101 = $

Answer 4

One thing is not sure.
you are not 7th std. Your question is bloated and unrealistic.
By such silly questions, do not loose ur credit. When u actually in need during real crisis, u will be help less.