Sci ~ Ch.40 Heat Flashcards
An example of heat energy changing into any other form of energy
Heat ➡️ kinetic energy
Heat➡️ light and sound
What is heat measured in?
Joules (symbol:J)
When solids,liquids and gases is heated,they _____.
Expand
When solids,liquids and gases are cooled,they ______.
Contract
Disadvantages of expansion and contraction:
- railway tracks need tapered joints
- slabs of concrete buckle in the heat if it has no room.
- bridges can get longer in summer than in winter
Advantages of expansion and contraction:
- thermometers
- Bimetallic strips➡️ used to trigger alarms and switch off heating. Made from 2 metals joined together.One metal expands faster than the other causing the strips to bend and break/complete circuit.
- expansion can be used in the car engine and in rockets
Why is it different with water?
Water contracts on cooling,only until it reaches 4 degreesC and if further cooled,water expands.
Advantages of water expanding when freezed
• fish can survive in lakes in the cold since water is most dense at 4*C and this “warm” water sinks and “colder” water is less dense and floats on top.
Disadvantage of water expanding when freezed
Water pipes can et burst if the water freezes.
Heat moves from a _____ object to a ____ object.
Warm ↪️ colder
3 ways that heat can be transferred is:
- conduction
- convection
- radiation
What is conduction?
Conduction is the method by which heat travels from particle to particle through a solid. E.g metals
What is an insulator?
An insulator is a substance which does not allow heat to flow through it easily. E.g. Wooden spoon
Gases (trapped air)
An example of a poor conductor of heat:
Water
Convection?
The transfer of heat through a liquid or gas when the particles of the liquid or gas move and carry the heat with them.
What is used to show convection currents in air?
A smoke box
Explain how a smoke box works.
- A taper ➡️ lit ↪️ blown out
- taper placed above the hole on the right
- Air above candle on the left heated➡️ expands↪️ less dense and rises
- colder air move in its place.
What chemical is required to test for convection in water?
Potassium permanganate crystal (purple dye)
Conclusion of testing for convection in water:
Water near crystal receive heat and expand first becoming less dense ↪️ floats to the top.their path is shown by the purple dye. Denser colder water replaces it➡️heated ↪️↪️ continues until all are heated. (Convection currents)
Radiation?
Radiation is the rapid transfer of heat from a hot object without needing a medium.
What is temperature?
A measure of the level of heat in an object
Whats the freezing point of water
0*C
Boiling point of water
100*C
When the pressure on water increases:
The boiling point increases.
When the pressure on water decreases:
The boiling point decreases
Each substance has its own ____ and ___
Melting and boiling point
Latent heat?
Latent heat is the heat taken in or given out when a substance is changing state without changing temperature.
What is heat?
Hear is a form of energy that can do work and change into other forms of energy.
