Heat Flashcards
What is the difference between heat and temperature?
Heat is a form of energy
Temperature measures heat
Give 3 advantages and 3 disadvantages of expansion and contraction
-Advantages
Thermometers
Bimetallic strips
Car engines and rockets
-Disadvantages
Railway tracks need tapered joints
Slabs of concrete buckle
Bridges can expand
How do you show that a solid expands when heated and contracts when cooled?
- Place a metal ball through a ring
- Heat the ball over a Bunsen burner
- Try to pass the ball through the ring
- Allow the ball to cool
- Check again to see if the ball will pass through
How do you show that a liquid expands when heated and contracts when cooled?
- Fill a flask and narrow glass tube with the liquid to half way up the tube. Mark this level with a pen
- Heat the flask in a water bath for a few minutes
- Note the new level of the liquid in the tube
- Allow the liquid to cool, observe the level of the liquid after several minutes
- The water moved up the tube when heated and returned to its original position when cooled
How do you show that a gas expands when heated and contracts when cooled?
- Set up long glass tubing in a flask of air going into a beaker of water.
- Heat the flask very gently with a hair dryer
- Note that bubbles appear at the end of the glass tubing in the beaker
- Allow the flask to cool and observe what happens
- A partial air vacuum is created as the the air particles escaped when heated and so once the air contracts water is pushed up the long tube into this empty space
What is conduction?
The method by which heat travels from particle to particle through a solid, e.g. along a metal spoon
What is an insulator?
An insulator is a substance which does not allow heat to flow through it easily
How do you show the transfer of heat by conduction and compare the conductivity of various substances?
- Set up copper, zinc, glass, wood, aluminium and iron rods coming from a metal container containing hot water
- Put small nails held with Vaseline on the end of each rod
- The nails drop at different rates showing the different rates that the metals conduct electricity at.
How do you investigate conduction in water?
- Trap a lump of ice with wire gauze at the bottom of a boiling tube
- Add ordinary tap water to the tube until it is 2 thirds full
- Heat the water at the top of the tube until it begins to boil and observe what happens to the ice
- The ice doesn’t melt showing water is a poor conductor of heat
How do you investigate convection in water?
- Set up a Bunsen burner under a beaker of water with glass tubing in it
- Drop a crystal of potassium manganate into the glass tubing
- Heat the beaker on a low Bunsen flame and observe what happens
- Convection currents are seen coming from the crystal as heat spreads throughout the water
How do you show the transfer of heat by radiation and that a dull black surface radiates heat better than a bright shiny surface?
- Pour equal amounts of hot water in a black and a white can
- Place a thermometer in each can
- Record the temperature from time to time in each can
- The temperature falls faster in the container with the dark surface. Therefore the a dark surface radiates heat better than a bright surface
What is latent heat?
Latent heat is the heat taken in or given out when a substance is changing state without changing temperature
What is conduction?
Conduction is the method by which heat travels from particle to particle through a solid
What is convection?
Convection is 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 radiation?
Radiation is the rapid transfer of heat from a hot object without needing a medium
