Energy and heating

• Energy is transmitted by conduction, convection or radiation.
• The conductivity of materials can be compared by examining the time taken to transmit energy through them.
• Energy is also transferred or transmitted from place to place as it moves through a substance.
• A conductor is a material that allows internal (thermal) energy to be transmitted through it easily.
• All metals are good conductors.
• When one end of a metal rod is put into a fire, the energy from the flame makes the ions in the rod vibrate faster.
• Since the ions in the solid metal are close together, this increased vibration means that they collide with neighbouring ions more frequently.
• More frequent collisions increase the rate of energy transfer.
• For example, if 2,000 J are transferred over a period of 10 s, then the rate of transfer is 200 J/s or 200 W.
• The cushion on a chair is an insulator, a material that does not allow charge or heat to pass through it easily.
• A metal seat at a railway station will feel cold as it conducts energy away from the passenger’s body, whereas a cushion on the chair would not allow energy to flow so easily.
• An insulator is a material that will not allow the easy flow of energy.