How long will it take to boil 1 liter of water?

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Homework Help Overview

The original poster attempts to determine the time required to boil 1 liter of water from an initial temperature of 20°C to 100°C, considering factors such as heat efficiency, voltage, and power. The problem involves concepts from thermodynamics and energy calculations.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the energy required to boil the water and the original poster's calculations. Questions arise regarding the transition from energy calculations to determining the time needed, with some participants offering hints about the relationship between power and energy.

Discussion Status

Participants are engaged in exploring the problem, with some providing guidance on the relationship between power and energy. The original poster expresses uncertainty about the next steps in the calculation process, indicating an ongoing exploration of the topic.

Contextual Notes

There is a focus on the efficiency of the heating process and the specific parameters provided, such as power and temperature change. The discussion also touches on the clarity of the task, specifically whether the goal is to bring the water to a boil or to boil it away completely.

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Homework Statement
How long will it take to boil 1 liter of water from 20°C? The heat efficiency / η is 85% , voltage / U 230V and power / P 200W. The answer must be given in seconds.
Relevant Equations
?
Hi.
I have been trying to solve the following problem:How long will it take to boil 1 liter of water from 20°C? The heat efficiency / η is 85% , voltage / U 230V and power / P 200W. The answer must be given in seconds.

So,

t1 = 20°C

t2 = 100°C

Δt = 80°C

V = 1,0 liter → m = 1,0 kg

ηkettle = 85%

U = 230V

P(the power needed to boil water) = 200W

So far I have solved the energy consumed in boiling water: E = c * m * ∆t = 334400_J (joules) Have I used the right formula? And what formulas can I use?

Hopefully, someone here can help me!
 
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Are you just supposed to bring it to a boil (begin boiling) or boil it all away?
 
I'm just supposed to bring it to a boil.

phyzguy said:
Are you just supposed to bring it to a boil (begin boiling) or boil it all away?
 
EMEE_ said:
I'm just supposed to bring it to a boil.
Then your calculation of the energy required looks correct. Do you know how to go from there to the time required? You will need to use the input power and efficiency.
 
phyzguy said:
Then your calculation of the energy required looks correct. Do you know how to go from there to the time required? You will need to use the input power and efficiency.

Ok, good if the calculation is correct! :). But I don't actually know how to go from there to the time required...
 
Hi EMEE:

Does it help to know that a watt is a joule per second?

Regards,
Buzz
 
Buzz Bloom said:
Hi EMEE:

Does it help to know that a watt is a joule per second?

Regards,
Buzz

Yeah, thanks, that might help. But I don't really know what formulas/ equations I should use... Could you please help with those?
 
If I'm going 50 miles per hour, and I have 300 miles to travel, how long will it take? If I'm putting in 200 Joules per second, and I need 334400 Joules, how long will it take?
 

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