People (at least in my house) run on tea and coffee, and that is why an electric kettle is important to us. Looking for the best tea kettles? We have a review you can use as reference.
If you drink a lot of coffee or tea, you’ll be grateful that someone had the foresight to design a super-efficient technique to turn cold water into hot water, namely the electric kettle (also known as an electric tea kettle).
Fill it with water, plug it in, and turn it on, and you’ll have piping hot water ready for drinking or cooking in a matter of minutes. How does a kettle function? Why is it taking so long for the water to boil? And how does it know when it’s time to shut down? Let’s have a look at it more closely!
What is an Electric Kettle?
Kettles are among the simplest of all household appliances. Look inside the water container and you’ll see a coil of thick metal called the heating element, at the very bottom. A large electric current flows into the heating element when you plug the kettle into an electrical outlet. Electrical energy is converted into heat by the element’s resistance (the tendency any material has to stop electricity flowing through it). Other words, the element becomes hot. In direct contact with cold water, the heat passes to the water by conduction and rapidly warms it up as well.
How Long Does a Kettle Take to Boil?
You can boil water in a variety of ways, including in a simple pan over an open fire or on a stove, but an enclosed kettle is usually faster because it prevents heat from escaping, allows pressure to rise faster (remember that water boils when its saturated vapor pressure equals atmospheric pressure), and aids in the rapid boiling of the water. But have you ever been annoyed by how long it takes your kettle to come to a boil? Don’t! The fact that your kettle boils so quickly is incredible, and here’s why.
When you keep pumping heat energy into the bottom of a kettle (faster than it escapes through the top and the sides), sooner or later the water inside will boil. It is a basic law of physics called conservation of energy that tells us that if you want to boil a liter of water, starting from the same temperature, you have to add the same amount of energy. It does not matter whether you use a camp fire or a kettle, a microwave or some amazing stirring device like James Prescott Joule (see box below), the amount of energy required to boil water is the same.
Let’s imagine you have 1 liter (approximately 1 kilogram, 2.2 lbs) of cold water at 10°C (50°F) that you wish to heat to its boiling point (100°C or 212°F). You’ll require 4.2 1000 grams of energy at 90 degrees, which equals 378,000 joules (378 kJ).
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The unexplained “4.2” refers to the specific heat capacity of water, which is a constant figure. Every substance has a unique specific heat capacity, which is the amount of energy required to raise the temperature of one gram of the material by one degree Celsius. To raise the temperature of 1 gram of water by 1°C, you must add 4.2 joules of energy, hence water’s specific heat capacity is 4.2 J/g/°C.
378kJ to boil a liter of water is rather more energy than you might think. An energy-efficient lamp rated at 10 watts uses 10 joules of energy every second (because 1 watt means using one joule per second), so it would take it 37,800 seconds about 10.5 hours to use as much energy as our kettle uses in a single boil!
When you use a 2400 watt electric kettle, it consumes 2400 joules of electrical energy per second while also putting (approximately) the same amount of energy into the water as heat each second. When you divide 378,000 by 2400, you get a time of roughly 160 seconds for the kettle to accomplish the job, which seems about appropriate because an electric kettle takes about 2–3 minutes to boil.
A saying says that a watched pot (kettle) never boils, yet that proverb stems from the days when most people boiled water over horribly inefficient open coal fires. Because it can deliver heat energy to the water considerably more quickly and efficiently, an electric kettle can boil water in just a few minutes.
If your kettle is rated at 2400 watts (W) and you’re using a 240 volt (V) power supply in the UK, the current flowing through the element will be 2400 / 240 or 10 amps (A). That’s a lot of current by home standards: the little charger I have for my iPod draws a maximum current of 0.67 amps, whereas the kettle uses 15 times that! The use of a reasonably large electric current is the answer to how an electric kettle works so quickly. Because the amount of heat produced is related to the square of the current, larger currents produce far more heat and heat objects much faster than smaller ones.
From below, you can see the concealed heating element of a typical modern kettle. (If you look closely) you can just see the two terminals of the element poking out on the bottom right corner of the light gray central part. The darker gray rim (where my thumb is) is a rubbery-plastic gasket that seals the heating element inside the bottom of the kettle and prevents water from leaking out. A long tube at the top carries steam from inside the kettle to a thermostat that turns off the element at the right time (see below).
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