A small appliance with a heating element: a kettle A kettle is designed to heat water quickly and efficiently.
Design and construction of a kettle
• Jug: a jug made from different materials, e.g. stainless steel or plastic, in a variety of colours and comes in various capacities/sizes, e.g. 1.7 litres. It may be a traditional dome or a modern jug shape.
• Tightly fitting lid: a tightly fitting lid can be opened or removed for filling.
• Spout: a spout that may have a filter to trap particles of limescale when pouring.
• Water level indicator: a water level indicator that shows the minimum and maximum water levels.
• Handle: a handle made of heat-resistant plastic. • On/off switch: an on/off switch controls the electricity supply. • Indicator light: an indicator light that shows if the kettle is in operation.
Flex
• Flex and a three-pin plug: a flex and a three-pin plug connect to the electricity supply. The flex can be connected to the kettle itself or to a removable base.
• Heating element: a heating element that heats the water inside the base of the kettle. • Thermostat: a thermostat automatically switches off the kettle when the water reaches boiling point.
HL Working principle of a kettle
• Heating element: when a kettle is plugged in and switched on electricity flows through the heating element, which offers resistance to the flow of electricity. This causes the element to heat up.
• Water heats: the heated element heats the water surrounding it by creating convection currents. As the water heats it begins to rise and the colder water at the top falls down to the base. It continues circulating until all the water reaches the same temperature.
• Thermostat: when the water reaches 100°C a thermostat integrated in the base will automatically turn off the flow of electricity to the kettle.
• Boil-dry device: most kettles contain a boil-dry device that automatically turns off the flow of electricity to the kettle if there is insufficient water to cover the element. This prevents overheating or an electrical fire.
Did you know ? Set out details of a study that you
have undertaken on a household appliance with a heating element. Refer to working principle. (6) HL
Kettles use a bimetallic thermostat that is made of two metals fused together. One metal expands quicker than the other, which causes the thermostat to change shape and cut off the power supply when it reaches boiling point.
