How Do You Calculate the Efficiency of a 2.5kW Electric Kettle?

firemama
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Homework Statement


A 2.5kW electric kettle takes 3 mins to raise the temperature of 1.2kg of water from a temperature of 20 degrees C to a temperature of 100 degress. The specific heat capacity of water is 4.2kJ/(kg K)


Homework Equations


So far I know that we're either using P=vit ot Q=mct
How do i find:
(a) enerygy output from 2.5kW heating element in a time of 3 mins, (b) efficiency of the heating.
 
Physics news on Phys.org


A kw is 1000 J/second

Calculate how much energy it took to heat the water and compare that with the answer from A
 
Thread 'Need help understanding this figure on energy levels'

Thread 'Need help understanding this figure on energy levels'

This figure is from "Introduction to Quantum Mechanics" by Griffiths (3rd edition). It is available to download. It is from page 142. I am hoping the usual people on this site will give me a hand understanding what is going on in the figure. After the equation (4.50) it says "It is customary to introduce the principal quantum number, ##n##, which simply orders the allowed energies, starting with 1 for the ground state. (see the figure)" I still don't understand the figure :( Here is...
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Thread 'Understanding how to "tack on" the time wiggle factor'

Thread 'Understanding how to "tack on" the time wiggle factor'

The last problem I posted on QM made it into advanced homework help, that is why I am putting it here. I am sorry for any hassle imposed on the moderators by myself. Part (a) is quite easy. We get $$\sigma_1 = 2\lambda, \mathbf{v}_1 = \begin{pmatrix} 0 \\ 0 \\ 1 \end{pmatrix} \sigma_2 = \lambda, \mathbf{v}_2 = \begin{pmatrix} 1/\sqrt{2} \\ 1/\sqrt{2} \\ 0 \end{pmatrix} \sigma_3 = -\lambda, \mathbf{v}_3 = \begin{pmatrix} 1/\sqrt{2} \\ -1/\sqrt{2} \\ 0 \end{pmatrix} $$ There are two ways...
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