Question
Which statement describes thermal conduction in a metal by electrons?
- Atoms and electrons move freely throughout the metal.
- Atoms and electrons vibrate about their fixed positions only.
- Electrons move freely throughout the metal.
- Electrons remain attached to atoms.
Answer/Explanation
Ans:
C
Question
Thermal energy is transferred by conduction in a metal bar.
Which statement is not correct?
Fast vibrating ions leave the surface.
Free moving electrons carry thermal energy through the bar.
Ions vibrate and strike neighbouring ions to make them vibrate.
Ions vibrate but do not change position.
Answer/Explanation
Ans: A
Question
Metals are good thermal conductors.
Insulators are poor thermal conductors.
Which description of the mechanism of thermal conductivity is correct?
-
In insulators, conduction takes place by electron transfer and molecular vibrations.
-
In insulators, conduction takes place by electron transfer only.
-
In metals, conduction takes place by electron transfer and molecular vibrations.
-
In metals, conduction takes place by electron transfer only.
Answer/Explanation
Ans: CQuestion
A teacher shows his class a polystyrene cup. The cup is made from thick plastic with lots of tiny air bubbles in it.
He asks the class why the cup is so good at keeping a hot drink warm. Three suggestions are made.
It contains air which is a poor thermal conductor.
The air is trapped in tiny bubbles so very little convection is possible.
The plastic is a poor thermal conductor.
Which suggestions are correct?
A 1 and 2 only
B 1 and 3 only
C 2 and 3 only
D 1, 2 and 3
Answer/Explanation
Ans: D
Question
A teacher demonstrates an experiment to a class. A boiling tube is filled with water and some ice
cubes are trapped at the bottom of the tube. The teacher then heats the boiling tube in the position
shown until the water at the top boils.
The ice does not melt.
What does this demonstrate?
A Water is a good conductor of thermal energy.
B Water is a good convector of thermal energy.
C Water is a poor conductor of thermal energy.
D Water is a poor convector of thermal energy.
Answer/Explanation
Ans: C