Energy transfer by heating

2.1 Energy transfer by conduction

• Energy transfer through a material by conduction depends on its thermal conductivity. The greater this is, the more energy per second it transfers by conduction.
• Good insulators need to have materials with low thermal conductivity, so energy transfer through them is as low as possible.
• Energy transfer per second through a layer of insulating material depends on:
  • temperature difference across material
  • thickness of material
  • thermal conductivity of the material
• To reduce energy transfer as much as possible:
  •  thermal conductivity of insulating material should be as low as possible
  •  thickness of insulating layer should be as thick as possible

Required practical

• Use different materials to insulate identical cans of hot water.
• The volume and temperature of the water at the start should be the same. Use the thermometer to measure the water temperature after a fixed time.
• The rods need to be the same length and width for a fair test. Each rod is coated with a thin layer of wax near one end and the uncoated parts are heated together.
• The wax melts fastest on the rod conducting energy the best
• Each rod has the same temperture difference between its ends; each rod is the same length and diameter

2.2 Infrared radiation

• Infrared radiation is part of the electromagnetic spectrum (electric and magnetic waves travelling through space). Infrared waves are longer in wavelength than visible light waves. Wavelength of light increases across the visible spectrum from blue to red light.
• The Sun emits electromagnetic radiation which is blocked by the Earth's atmosphere.
• All objects emit infrared radiation.
• The higher the temperature of an object, the more infrared radiation it emits out in a given time.
• A body at constant temperature emits infrared at the same rate as it absorbs it.
• A perfect black body is an object absorbing all the radiation hitting it. No radiation is reflected or transmitted. They are good emitters and absorbers. Radiation emitted by a perfect black body is called black body radiation. The intensity of radiation is highest at a certain wavelength, depending on the temperature.
• If temperature rose, the intensity of radiation emitted is the same…