Calculating Power and Energy Consumption of Two Coffee-Makers

In summary, when two 15Ω coffee-makers are connected to a 120V power supply for two hours a day each, the total power consumed is 0.96 kW and the total energy consumed is 3.84 kWh. This is equivalent to one coffee-maker running for four hours.
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Homework Statement


Two 15Ω coffee-makers are connected to a 120V power supply for two hours a day each. Find the power and energy.

Homework Equations


P=V2/R
ΔE=PΔt

The Attempt at a Solution


I am assuming, since there are two coffee-makers connected to one 120V power supply, that:
P = V2/R = 1202V/30Ω = 480W or 0.48kW

ΔE = PΔt = 0.48 kW x 2h = 0.96 kWh

Can someone confirm?
 
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  • #2
Are the coffee makers somehow connected in series? If they are standard appliances, won't they each have to run on 120 V?
 
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  • #3
gneill said:
Are the coffee makers somehow connected in series? If they are standard appliances, won't they each have to run on 120 V?
Hmm makes sense. Therefore,
P = V2 / R = 1202 / 15 = 960 W or 0.96 kW
Then I would multiply this by 2, since there are two coffee-makers?
0.96 x 2 = 1.92 kW

ΔE = PΔt = 1.92 kW x 2h = 3.84 kWh
 
  • #4
Yes! :smile:
 
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  • #5
I am confused over the 2 hours each though...
Would that mean that one coffee-maker runs on 120 V for 2 hours, as well as the second?
So my total time should actually be 4h?
ΔE = PΔt = 1.92 kW x 4h = 7.68 kWh
 
  • #6
One coffee maker running for four hours consumes as much power as two coffee makers running for 2 hours.

On edit: Oops, I made a mistake. I meant to say that one coffee maker running for four hours consumes as much energy (not power) as two coffee makers running for 2 hours. :oops:
 
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  • #7
Thank you for your help, I understand now! :smile:
 

What is the difference between power and energy?

Power is the rate at which energy is used or transferred, while energy is the total amount of work that can be done. In other words, energy is a measure of the capacity to do work, while power is a measure of how fast that work can be done.

How do you calculate power?

To calculate power, you need to know the amount of work done (W) and the time it took to do the work (t). The formula for power is P = W/t, where P is power in watts (W), W is work in joules (J), and t is time in seconds (s).

What is the unit of measurement for power?

The unit of measurement for power is watts (W). One watt is equal to one joule of energy per second.

How do you calculate energy?

To calculate energy, you need to know the power (P) and the time (t). The formula for energy is E = P*t, where E is energy in joules (J), P is power in watts (W), and t is time in seconds (s).

What is the difference between average power and instantaneous power?

Average power is the total power used or transferred over a certain period of time, while instantaneous power is the power at a specific moment in time. Average power is calculated by dividing the total energy by the total time, while instantaneous power is calculated using the formula P = dW/dt, where dW is the change in energy and dt is the change in time.

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