Transfers of thermal energy (2A 10) Flashcards
What is heat transfer?
It is when two objects are in contact, heat energy is transferred from the hotter object to the colder
What is expansion?
when a substance is heated, it gains heat and expands (increase in volume)
What is contraction
when a substance is cooled, it loses heat and contracts (decrease in volume)
What is a bimetallic strip?
A bimetallic strip is made of two metals that expand and contract at different rates upon the same changes in temperature.
What causes the bimetallic strip to bend?
Brass expands and contracts more than steel, which will cause the strips to bend.
How will a bimetallic strip open a circuit?
When an oven is heated to the set temperature, brass expands more than steel, the bimetallic strip will bend downwards. The circuit becomes open to stop further heating.
How does a bimetallic strip bend when its heated/ cooled?
The bimetallic strip will bend downwards when it is heated as brass expands more than steel.
It bends upwards when it is cooled as brass contracts more than steel.
However this depends on the position of brass.
What are the different ways heat energy can be transferred from one place to another?
Conduction, radiation and convection
How is a sea breeze formed?
Hint: in the day
The sun heats up the land, which in turn warms the layer of air above it. The warmer air is less dense and rises.
During the day, the land heats up more than the sea.
The cooler air above the sea is more dense,sinks and moves in to replace the air above the land. This movement of air current sets up a sea breeze.
What is radiation?
Radiation is the transfer of infrared radiation from a hot body to a cooler body without the need for a medium.
Why are solids better conductors than liquids and gases?
Solids are better conductors of heat because the particles in solids are arranged more closely to one another than then the particles in liquids and gases.
The close arrangement of particles in solids in enables the transfer of heat energy more quickly.
** what is convection?
Convection is the transfer of heat energy from one place to another by the physical movement of a medium.
** explain why the heating element is placed at the bottom of the kettle
Water nearest to the heating element will gain heat energy, expand and rise due to the lower density. As the hot water rises, the more dense cold water will sink and be heated by the heating element. This produces a convection current that heats all the water evenly.
**Suggest why the frozen pack is placed at the top of the box rather than at the bottom.
Air near the ice pack loses heat energy, contract, and become more dense and sink. The warmer and less dense air at the bottom of the box will rise and eventually become cooled by the frozen pack. A convection current is thus set up, cooling the whole box.
The wall of the box is double layered. Explain why the food in the box can be kept for a longer time if air trapped between the layers.
Air is a poor conductor of heat. The trapped air will slow down the rate of conduction of heat loss/gain to keep the contents hot/cold. For this example, is to prevent/reduce heat gain to keep contents cold.
