Unit 5.3--Heat Transfer Flashcards
(28 cards)
What is heat?
The energy transferred from a hotter object to a colder one
What does conduction require?
A medium
Give examples of medium for conduction.
Solid, liquid, gas
When can conduction take place?
Two objects that are in contact
How can heat be transferred by conduction?
Through an object from the hotter end to the colder end
Which groups of material, metals or non-metals, conducts heat faster? Give a reason to support your answer.
Metals. They have free electrons.
Explain why the materials used in an experiment are of the same length and thickness.
To ensure that the experiment is a fair test
What do we call an object if it conduct heat fast?
A good conductor
What do we call poor conductors of heat?
An insulator
Refer to the experiment in the textbook:
Is water a good conductor of heat?
No. The ice does not melt when the water at the top boils. This shows that heat is not readily transferred through water from the top to the ice.
Refer to the experiment in the textbook:
Is air a good conductor of heat? Explain your answer with reference to Candle X (which is lit) and Candle Y (which is held closely to Candle Y)
No. Candle Y does get hot enough to melt. This shows that heat from the flame is not readily transferred through air to Candle Y.
Y/N:
Are water and air good conductors of heat?
No
Give examples of uses of good conductors of heat and give its advantages and purposes. (2)
Cooking utensils— transfer heat very quickly to the food and reduces cooking time
A heat sink— conduct heat away to prevent the computer from overheating
Give examples of uses of poor conductors of heat and explain why it works. (Only state the above for the second example)
Handles of cooking utensils
Fur and feathers — can trap a lot of air inside them. Since air is a poor conductor f heat, we can wear fur or down clothing to keep warm. Similarly, animals like polar bears keep warm by trapping air in their fur.
Where can convection take place?
In liquids and gases
How is heat transferred in water and air?
When water/air is heated form below, the hot water/air rises and at the same time, the cold water/air sinks to replace the ho water/air.
What do we call the movement fo water in convection?
A convection current
Describe the convection which takes place in water.
When heated, the hot water rises. At the same time, the cold water in the tube sinks to take the place of the risen hot water.
Describe the convection which takes place in gas.
When the air above the flame gets hot, it rises. The cold air form the surroundings sinks to take the place of the hot air.
Give 2 examples of the applications of convection in electrical appliances. Briefly explains how it works.
An electric kettle: hot water rises, cold water sinks
An air conditioner: hot air rises, cold air sinks
Give an example of phenomena showing conversion of heat in Nature. Explain how it is affected by convection.
Sea breezes and land breezes.
During the day, land hotter than sea— land absorbs heat from the Sun faster than sea water (hot air rises form land and cold air blows in from sea to replace the hot air that has risen) —> sea breezes
At night, land colder than sea— land cools down faster than the sea and land becomes colder (hot air rises from sea and cool air blows from land to sea) —> land breezes
Where can radiation take place?
In a vacuum
Why does the temperature of an object increases?
It is because it absorbs radiation
Why is it more comfortable to wear light-coloured clothes in summer?
It is because light-coloured clothes absorb less radiation from the Sun than dark-coloured clothes. Thus, light-coloured closets help us stay cool in summer.
