Modes of heat transfer

📋 Teacher notes

• •Particles do NOT travel down the rod — they vibrate in place and pass energy to their neighbours, like a row of people jiggling a rope.
• •Metals conduct well because free (delocalised) electrons carry energy quickly through the lattice; non-metals lack these free electrons.
• •Rate of heat flow: Q/t = kAΔT/L — bigger area or ΔT speeds it up, a thicker (longer) barrier slows it down. This is exactly why we use thick walls and small windows to keep buildings warm.
• •Compare copper (k≈385) with glass (k≈0.8): copper conducts about 480 times faster — try both in the material list.
• •Trapped air (double glazing, wool, fur) is a poor conductor and makes an excellent insulator, precisely because it has such a low k.