# Homework Help: Basic question about the power rating of a kettle

1. Jan 6, 2014

### JohnBarnes4260

1. The problem statement, all variables and given/known data
Hello all. I am very new to learning about science and i've been given a question in my homework about power ratings and heat transfers. Basically the question is, on an electric kettle why is the power rating given as (e.g) 1500W - 2000W instead of just a single figure.

3. The attempt at a solution

Is this because a fixed amount of water takes less power to heat up at lower temperatures and so the kettle works up to its maximum wattage as needed?

2. Jan 6, 2014

### Staff: Mentor

I don't think I've ever seen a kettle so marked, but for the sake of the exercise we can assume that it is so.

The answer expected may depend upon the material of the course it's associated with. What is the course and what is the current topic where the question arises?

Kettles work by passing electric current through a resistive heating element (essentially a resistor). It gets hot thanks to the power dissipated, and heat generated is shed into the water thus heating that water. Usually the resistance of the element is pretty much fixed when it's at or near its "working temperature".

Ask yourself what can vary in the operating conditions for the kettle, keeping in mind the material of the chapter under study.

3. Jan 6, 2014

### rude man

Maybe because the kettle has more than one power setting.

Or, sloppy quality control of the heating element. Actually, a 2000W kettle would blow a 15 Amp circuit breaker. I haven't seen any appliance rated at more than 1500W operating from a common houshold receptacle.

But it could also be due to varying voltages. At 125V the power is (125/110)^2 x 1500 W = 1940W, close to 2000W, if it's 1500W at 100V.
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