Heat - presentation for JUNIOR CERT science.pptx

Covers topic of heat for jc science

1. Heat

2. To be able to understand what Heat is and why it is a form of energy. To be able to understand the effect that heat has on certain materials – expansion and contraction. To be able to understand the effect of expansion and contraction on solids through experimentation and demonstration. Learning Outcomes

3. Heat is a form of energy. Why? Because heat causes things to move. What things move because of heat? What is Heat?

4. Heat can be converted into other forms of energy: In power stations, fossil fuels are burned to produce heat. This heat produces steam which turns the blades of a turbine. The turbine produces ELECTRICAL ENERGY. What is Heat?

5. The Sun gives off both LIGHT ENERGY and HEAT ENERGY. Plants take in sunlight and use it for Photosynthesis. The heat energy is changed to chemical energy. Why? What is Heat?

6. Most materials expand when heated. e.g. Gaps are left in railway tracks so that the tracks don’t buckle when they get hot. Concrete footpaths crack and buckle when they get too hot. Expanding

7. Most materials contract when cooled. e.g. high voltage cables contract when cooled to avoid them snapping in winter. footballs lose the air inside them when they are left out in the cold – the air contracts. Contracting

8. To investigate the expansion and contraction of solids when heated and cooled To investigate the expansion and contraction of liquids when heated and cooled. To investigate the expansion and contraction of gases when heated and cooled. Mandatory Experiments

9. Title: To investigate the expansion of solids when heated and contraction when cooled. Equipment: Retort stand, ball and ring, Bunsen burner. Diagram: Solids

10. Method: 1. Test to see that the ball fits through the ring at the beginning of the experiment. 2. Heat the ball over the Bunsen burner for 4 minutes. 3. Using tongs see if the ball fits through the ring now that it’s been heated. 4. Allow the ball to cool for 10 minutes. 5. See if the ball fits through the ring now it’s been cooled. Result: The ball doesn’t fit through the ring when it’s heated as it has expanded. The ball now fits through the ring cold as it has contracted.

11. Title: To investigate the expansion and contraction of liquids when heated and cooled. Equipment: Retort stand, round-bottomed flask, glass tube, food dye, Bunsen burner. Liquids Diagram:

12. Method: 1. Fill a round-bottomed flask with water that has had food dye added to it. 2. Insert a stopper and glass tube in the flask. 3. Hold the flask in place with clamps. 4. Heat the flask with the Bunsen burner for a few minutes. 5. Remove the Bunsen burner from underneath the flask. 6. Observe the level of water in the glass tube over a period of time. Result: The coloured water rose to the top of the tube because of expansion due to heating. The level of water dropped because the water contracted due to cooling.

13. Title: To investigate the expansion of gases when heated and contraction when cooled. Equipment: Retort stand, round-bottomed flask, glass tube, Bunsen burner, beaker of water Gases Diagram:

14. Method: 1. Insert a stopper into the top of the flask. 2. Set up the apparatus as shown using clamps and a retort stand. 3. Make sure the glass tube is below the level of water in the beaker. 4. Gently heat the round-bottomed flask. 5. Observe the glass tube in the beaker. 6. Take away the Bunsen burner. 7. Observe the glass tube. Result: Bubbles of air in the water come from the glass tube. This is due to expanding gas. The water rises in the glass tube. This is due to contracting gas.

15. We now know all solids, liquids and gases can expand and contract. However, not all of these things expand and contract by the same amount. This is the basis behind the bimetallic strip. Bimetallic strip

16. A bimetallic strip is made up of two metals – that’s why it’s called “bimetallic” (meaning two) They are used to switch off electrical circuits in response to temperature changes For example when you set your heating for a certain temperature, it will cut off the circuit when it reaches that temperature.

17. We now know materials expand when heated and contract when cooled. Water doesn’t behave the same way. Water Water at 6ºC Water at 4ºC Water at 2ºC

18. If you heat water above 4ºC, it EXPANDS. If you cool water below 4ºC, it EXPANDS. Above 4ºC, water behaves like all other liquids. Below 4ºC, water behaves oppositely to all other liquids. Water at 6ºC Water at 4ºC Water at 2ºC

19. If you continue to lower the temperature, the water will continue to expand. At 0ºC, water turns into a solid form. What is it called? Because of expansion, the volume of ice will be bigger than the volume of water. This is why ice is less dense than water – will it float or sink? What happens when water freezes?

20. Expansion of water when frozen explains why water pipes can burst easily in cold weather. In very cold weather, lakes freeze. Because ice is less dense than water, where does it form? This ice acts as a barrier so that the water underneath doesn’t freeze. This allows fish to survive. Ice

21. Temperature is a measure of the hotness of an object. The unit for temperature is the degree Celsius ( °C) – is there any other units? You can measure the temperature of liquids and solids using a thermometer. Temperature

22. Our body temperature should be 37 °C Room temperature should be around 20 °C

23. To find out melting and boiling points of liquids, you take their temperature when they begin melting or boiling. Let’s take water as an example. Melting and Boiling Points

24. How would you find out these points? What would you need to determine it? Melting and Boiling Points of Water

25. Heat is a form of energy – the unit of heat is Joules (J). So what is the difference between Heat and Temperature? Temperature is the measure of the hotness of a body – the unit of temperature is degree Celsius ( ⁰C)

26. We have seen before that when things are heated, their temperature goes up. However, there are situations where things are heated and temperature doesn’t go up. Latent Heat

27. This is because the heat is causing a change in the state of the material (solid, liquid, gas) When this happens, we call this LATENT HEAT. Latent Heat

28. Basically, how do we go from a solid to a liquid, or a liquid to a gas? So how do we apply latent heat? Time (minutes) 1 2 3 4 5 6 7 8 9 10 11 12 Temp. ( ⁰C) -5 -2 15 30 45 60 75 90 100 100 100

29. This is where the ice changes from solid to liquid – to water This is where the water changes from liquid to gas – to steam

30. It is easy to see that heat doesn’t stay in one place – it moves from one place to another. It can travel by three ways: Conduction Convection Radiation Heat Transfer

31. Conduction is when heat travels along atoms in a material. The energy is passed from atom to atom in the material. The faster the energy is passed through the atoms, the better a conductor the material is. Conduction

32. Convection is when heat travels through liquids and gases. When liquid and gas molecules get hot, they move around and take the heat with them. Convection

33. Heat transferred by radiation doesn’t need a medium – doesn’t need a solid, liquid or gas. All hot objects emit heat by radiation – The Sun. Radiation

34. To show the transfer of heat energy by conduction in solids. To show the transfer of heat energy by convection in liquids. To show the transfer of heat energy by radiation. To investigate conduction and convection in water. Mandatory Experiments

35. Title: To show the transfer of heat energy by conduction in solids. Apparatus: Conduction apparatus, wax, pins, boiling water Diagram: Conduction

36. Method: 1. Set up as shown. 2. Pour boiling water into the container. 3. Watch the drawing pins at the end of the rods and note what order they fall off. Result: As the rods heated up, the pins fell off them because the wax melted. The first pin to fall off was stuck to the best conductor. Conclusion: Heat was conducted along the rods. Some materials are better conductors than others.

37. Title: To show the transfer of heat energy by convection in water. Apparatus: Bunsen burner, dye, beaker of water. Convection Diagram:

38. Method: 1. Set up as shown. 2. Place a small crystal of dye in the beaker. 3. Gently heat the water. 4. Observe what happens. Result: As the water is heated, convection currents start in the water. The dye shows us these currents. Conclusion: Heat travels in water by convection

39. Title: To show the transfer of heat by radiation. Apparatus: Two metal cans (one shiny can, one black can), two thermometers, boiling water. Diagram: Radiation

40. Method: 1. Set up as shown. 2. Pour equal amounts of boiling water into each can. 3. Record the temperature in both cans every two minutes. Result: The temperature dropped in both cans due to heat loss from radiation. The black can lost heat faster than the shiny can. Conclusion: Heat travels by radiation.

41. Title: To investigate conduction and convection in water. Apparatus: Bunsen burner, test tube, water, ice cube, coin . Conduction & Convection in Water Diagram:

42. Method: 1. Set up as shown. 2. Heat the water at the top of the test tube. 3. Remove the weight from the test tube. 4. Heat the bottom of the test tube. Result: The water at the top boils but the ice doesn’t melt – the heat doesn’t travel to the bottom. All the water boils when the bottom of the test tube is heated. Conclusion: Water is a poor conductor of heat. Heat travels in water by convection.

43. If a material isn’t a good conductor – like wood – it is said to be a good insulator. An insulator is a material that is a poor conductor of heat – it holds heat in well. Examples are: Insulators