Conduction of heatConduction of heat

TargetTarget

To know how heat flows by conduction in To know how heat flows by conduction in substances.substances.

Saturday 8 April 2023

Thinking taskThinking task

Why does a piece Why does a piece of metal feel cold of metal feel cold but a piece of wood but a piece of wood at the same at the same temperature feels temperature feels warm?warm?

Answer: The metal conducts heat away from the hands but wood stops heat flowing from the hand.

Experiment to show conduction of heatExperiment to show conduction of heat

Attach some drawing Attach some drawing pins to a metal rod pins to a metal rod using Vaseline.using Vaseline.

Heat the rod with a Heat the rod with a Bunsen flame – when Bunsen flame – when the heat reaches the the heat reaches the pins the Vaseline melt pins the Vaseline melt and the pins fall off. and the pins fall off.

Showing conductionShowing conduction

The experiment showed The experiment showed how heat was conducted how heat was conducted through a metal rod.through a metal rod.

There are moving particles (electrons) inside the metal – the faster they move the higher the temperature – they bump into each other to allow the heat to flow through the metal.

Liquids are poor conductors of heat [insulators].

WEAR SAFETY GLASSES

What about gases?

Carefully put your finger 1cm away from a Bunsen burner flame.If gases were good conductors, you’d burn your finger - you don’t.Gases are good insulators.

Conduction

Copy this summary table into your book :

Material Conductor or Insulator ?

Metals very good conductors

Non-metals Insulators

Liquids Insulators

Gases Good insulators

Vacuum Excellent insulator

Conduction

Bad points about conductionBad points about conduction

Allows heat to flow Allows heat to flow out of buildings in out of buildings in winter.winter.

Can cause burns when Can cause burns when touching something touching something hot (pan handle).hot (pan handle).

Good points about conductionGood points about conduction

Allows heat Allows heat to flow to flow through the through the bottom of a bottom of a cooking pan.cooking pan.

Using insulatorsUsing insulators

We put gloves and We put gloves and jumpers on to keep jumpers on to keep warm in winter.warm in winter.

We use place mats to We use place mats to protect tables from protect tables from damage from hot plates.damage from hot plates.

We reduce heat loss We reduce heat loss from houses with loft from houses with loft insulation.insulation.

A model for conductionA model for conduction

In metals ‘free’ electrons easily carry In metals ‘free’ electrons easily carry the kinetic energy from one side to the the kinetic energy from one side to the other.other.

In non metals inter atomic collisions In non metals inter atomic collisions are needed to carry the kinetic energy are needed to carry the kinetic energy from one end of the material to the from one end of the material to the other.other.

Questions: Hodder B Pages 28 and 29