Why are cooking utensils generally made of metals?
Answer
Because metals are good conductors of heat. A material that lets heat pass through it easily is called a good conductor, and all metals belong to this group — a fact you met in the chapter ‘The World of Metals and Non-metals’.
Why it happens: when a metal pan is put on the flame, the particles of the metal touching the flame get heated first. Each heated particle passes the heat on to the particle next to it, and in this way heat travels quickly from the bottom of the pan into the food. This process is called conduction. A pan made of wood or clay would hardly let the heat through, and Pema's grandmother could never cook thukpa in it.
Tip: notice that the handle of a good pan is made of wood, plastic or bakelite — poor conductors — so that the heat does not reach your hand.
Q2.
How does heat get transferred in these materials?
Answer
In a solid metal, heat is transferred by conduction — from the hotter part of the object to its colder part.
Hot end of the metal → particle gets heated Heated particle → passes heat to its neighbour Neighbour → passes it on further … and so on, until the cold end also becomes hot
Why it happens: the particles of a solid are tightly packed and cannot move from their places. So they cannot carry the heat along with them. What they can do is vibrate faster when heated and shake up the particle next to them. Heat therefore travels through the material while the particles themselves stay where they are. Activity 7.1, with the pins falling one after the other, shows exactly this.