Answers to Entrance Activity for 4.7

Answers...

1.             What is the most common heat transfer mechanism in solids?

Conduction

2.             What is the most common heat transfer mechanism in liquids and gases?

Convection

3.             What is the only heat transfer mechanism in a vacuum?

(Infra-red) Radiation

4.             Why can't conduction happen in a vacuum?

There are no particles in a vacuum to transfer the vibrations

5.             What happens to the space between the particles in a gas when you heat it?

The space between the particles increases

6.             What happens to the density of a gas when you heat it?

It decreases because the space between the particles increases

7.             Why can't convection happen in a solid?

In a solid the particles are fixed in position and are not free to move

4.6 - Recall that energy transfer may take place by conduction, convection and radiation

4.6 recall that energy transfer may take place by conduction, convection and radiation

Task 1
· Try the animation: particle model - conduction
· Extension: what is the limitation of this animation? (Check your answer with the Heating a Solid animation)

The limitation is that the animation does not show that the object expands when it is heated.

Task 2
· Try the quiz on the Cooking animation
· Extension: what's the mistake in the description of convection?

The animation states that the molecules at the bottom of the liquid heat up and they start to rise, when they cool down the molecules shrink again and sink. This creates a convection current and gradually all of the liquid heats up.

This is wrong because if you heat a liquid from below, the liquid at the bottom gets heated up and it expands. The liquid then rises because it has a lower density, afterwards the cool liquid (at the top) sinks to the bottom where the heat source is and it then expands and rises. The process is repeated. This is called convection current.

Particle model - conduction.swf Download this file

Cooking using Conduction, Convection and Radiation - interactive animation.swf Download this file