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JArcadia7
Joined: 04 Mar 2015 Posts: 1 Location: Pennsylvania

Posted: Fri Mar 06, 2015 1:53 am Post subject: Current and Heat 


Some stoves use the heat produced by current flowing through a conductor. If the heating element (conductor) has a resistance of 30 ohms, how long will the burner have to work to heat 500 g of 30°C water up to its boiling point? The specific heat of water is 4.19 x 103 J/kg·°C, and the household voltage is (120V).
How do I solve this? Which formula's do I have to use? 

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hepcj Site Admin
Joined: 23 Jun 2007 Posts: 125

Posted: Tue Mar 10, 2015 2:08 am Post subject: 


To solve this you need to find the energy required to heat the mass of water to 100 deg, from 30 deg.
$$E= mc\delta\theta$$
The power of the heater is the amount of energy it can produce in one second and this is given by \(P= I^2 R\). But you don't have the current, so you use Ohm's law V=IR to substitute for I.
So the power will be \(V^2/R\)
To find how long it takes, divide the energy required by the power. 

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