M. Manser (2014)

Module P1:  Cooking with infrared and with microwaves (comparing) *[6 mark question] M. Manser Sackville School

compare cooking using microwaves with using infrared radiation describe how microwaves and infrared transfer energy relate the energy of microwaves and infrared to their frequency

Every mobile phone conversation involves the transmission of microwave signals. The wavelength of microwaves ranges from 30 cm (the length of a standard ruler) to 1 mm (about the size of a full stop). Microwaves have many uses. How many can you think of? micro- waves radio waves infrared 1000 m1 mm1 m1 m0.001 mm ultra- violet wavelength of electromagnetic waves Microwaves are a form of electromagnetic radiation. They are very short-wavelength radio waves.

We experience infrared waves everyday in the form of heat. infrared microwaves 10 mm0.001 mm0.1 mm mm visible light wavelength of electromagnetic waves Infrared waves have wavelengths between 1 mm (about the size of a pin head) and about mm (about the size of a cell). Infrared radiation is a form of electromagnetic radiation that lies between microwaves and visible light on the electromagnetic spectrum.

Infrared radiation is emitted by all objects but is not visible to humans. The hotter an object is, the more infrared radiation it emits. Infrared radiation can be detected by special cameras. A thermogram shows how objects with different temperatures emit different amounts of infrared radiation. Here, the white areas are warmest and the blue areas are coldest. As an object gets hotter, visible light is also emitted. This is what can be seen when an object glows ‘red hot’.

The infrared radiation emitted by the Sun, radiators, solid fuel fires and electric fires is used for heating. Grills, cookers, toasters, campfires and barbecues use infrared radiation to cook food. The heating effect of infrared radiation is detected by temperature sensitive nerve-endings in skin. Infrared waves are emitted by the heating element or lit fuel and absorbed by the surface of the food. Heat is transferred through the food by conduction.

M. Manser Invicta Grammar School Microwaving IR cooking Energy absorbed strongly by all molecules Energy not absorbed by glass or plastic container, or walls of the oven. Can penetrate up to 1cm into the food, depending on its density Faster, more efficient Food must be stirred to distribute the heat evenly Food must be rested before eating to ensure complete cooking Some energy used to heat container and air and wire racks in the oven Absorbed by molecules on the surface only Energy absorbed strongly by water molecules Silver containers or foil covers may be used safely Slower, less efficient Uses electromagnetic waves Conduction or convection transfers the heat to the centre of the food The particles which absorb the energy show an increase in KE