1 Book 1 Section 4.1 ConductionRoasted chestnuts Conduction in solids, liquids and gases Conduction and particle motion Check-point 1 Examples of conduction and insulation Factors affecting the rate of conduction Check-point 2 1 2 3 4 Book 1 Section 4.1 Conduction

2 Book 1 Section 4.1 ConductionRoasted chestnuts In preparing roasted chestnuts, raw chestnuts are fried together with black sand in a large iron wok. Book 1 Section 4.1 Conduction

3 Book 1 Section 4.1 ConductionRoasted chestnuts Why is an iron wok suitable? Iron wok is a good conductor of heat Why is black sand added? To improve conduction of heat to chestnuts Book 1 Section 4.1 Conduction

4 1 Conduction in solids, liquids and gasesWhen we cook food using a pan, heat is transferred to the pan and to the food through direct contact.  conduction Expt 4a Conduction in solids, liquids and gases Book 1 Section 4.1 Conduction

5 Book 1 Section 4.1 ConductionExperiment 4a Conduction in solids, liquids and gases How does heat transfer along a solid rod? Set up the apparatus. Use the same amount of wax to stick drawing pins along the copper rod. Heat one end of the rod. copper rod insulating board drawing pins What happens to the drawing pins? Book 1 Section 4.1 Conduction

6 Book 1 Section 4.1 ConductionExperiment 4a Conduction in solids, liquids and gases What kind of solid conducts heat faster? Put a copper rod, an iron rod, a glass rod and a wooden rod into a beaker of hot water. Feel the ends of the rods. Which rod gets hot first? very hot water glass wood iron copper Book 1 Section 4.1 Conduction

7 Book 1 Section 4.1 ConductionExperiment 4a Conduction in solids, liquids and gases What kind of solid conducts heat faster? Set up the apparatus. (The rods are of same thickness and length). Heat the ends of the metal rods. aluminium copper iron drawing pins Which drawing pin falls first? Book 1 Section 4.1 Conduction

8 Book 1 Section 4.1 ConductionExperiment 4a Conduction in solids, liquids and gases Does water conduct heat fast? Use wire gauze to keep some ice under water at the bottom of a boiling tube. Gently heat the top part of the water. Does the ice melt? water wire gauze ice boiling tube Book 1 Section 4.1 Conduction

9 Book 1 Section 4.1 ConductionExperiment 4a Conduction in solids, liquids and gases Does air conduct heat fast? thermometer cardboard tube heater Set up the apparatus. Take the reading of the thermometers after a while. Is air a good conductor? Book 1 Section 4.1 Conduction

10 Book 1 Section 4.1 ConductionExperiment 4a Conduction in solids, liquids and gases Video Video Video Video Video 4.1 Expt 4a - Conduction in solids, liquids and gases Book 1 Section 4.1 Conduction

11 1 Conduction in solids, liquids and gasesExpt 4a shows that solids, liquids and gases conduct heat at different rates. Metals are good conductors of heat. Non-metals are poor conductors, or good insulators. Book 1 Section 4.1 Conduction

12 1 Conduction in solids, liquids and gasesThe Expt 4a also shows that… …heat is transferred from a region of higher temp to a region of lower temp. Conduction is the transfer of heat from the hot part to the cold part of an object. Energy (but not matter) is transferred in the process. Book 1 Section 4.1 Conduction

13 1 Conduction in solids, liquids and gasesDoes the orientation of the rod matter? Example 1 Book 1 Section 4.1 Conduction

14 Book 1 Section 4.1 ConductionExample 1 Does the orientation of the rod matter? Phoebe heats two identical metal rods. Which rod will heat up first? Why? They heat up at the same rate. Energy transferred from the hot end to the cold end by conduction is NOT affected by the orientation of the rod. Book 1 Section 4.1 Conduction

15 2 Conduction and particle motionAll matter is made up of atoms, each of which has a nucleus with electrons moving around. Book 1 Section 4.1 Conduction

16 2 Conduction and particle motionWhen one part of a solid is heated, the atoms there vibrate faster and gain KE. The slower neighbouring atoms are hit.  vibrate more rapidly  Temp of the neighbouring parts  atoms are closely packed, can only vibrate to and fro Simulation 4.1 Conduction and particle motion Book 1 Section 4.1 Conduction

17 2 Conduction and particle motionThis process takes place in all solids, but…. The rate of energy transfer across an object by this process is slow. In metals, the loosely held outermost electrons can move freely among the atoms.  free electrons Book 1 Section 4.1 Conduction

18 2 Conduction and particle motionWhen one part of a metal is heated, the free electrons there move faster and collide with the neighbouring atoms.  temp of the colder parts  This process is rapid  very high rate of conduction of metals. Book 1 Section 4.1 Conduction

19 2 Conduction and particle motionIn liquids and gases, the atoms are not strongly held together. Faster atoms cannot hit cannot pass on energy to neighbouring atoms effectively. Liquids and gases are poor conductors of heat. 4.2 Microscopic description of conduction in matters Simulation Book 1 Section 4.1 Conduction

20 Book 1 Section 4.1 Conduction2 Conduction and particle motion Houses in desert Example 2 Book 1 Section 4.1 Conduction

21 Book 1 Section 4.1 ConductionExample 2 Houses in desert In a desert, it is hot in the daytime and cold at night. The walls of houses there are often made of mud. It is important that the walls are thick. Book 1 Section 4.1 Conduction

22 Book 1 Section 4.1 ConductionExample 2 Houses in desert (a) What is the direction of the flow of heat through the wall in the daytime? From outside to inside. (b) What is the direction of the flow of heat through the wall at night? From inside to outside. Book 1 Section 4.1 Conduction

23 Book 1 Section 4.1 ConductionExample 2 Houses in desert (c) Explain how the thick mud walls help maintain the temp of the house. Mud is a poor conductor. A thick mud wall keeps the house… warm at night by slowing the flow of heat from inside to outside. cool in the daytime by slowing the flow of heat from outside to inside. Book 1 Section 4.1 Conduction

24 Book 1 Section 4.1 ConductionCheck-point 1 – Q1 In conduction, in which of the following directions is energy transferred? A From high-temp area to low-temp area. B From low-temp area to high-temp area. C From area of high internal energy to that of low internal energy. D The direction is different in metals and non-metals. Book 1 Section 4.1 Conduction

25 Book 1 Section 4.1 ConductionCheck-point 1 – Q2 Most metals are good conductors because A their atoms are closely packed. B their atoms vibrate faster when heated. C there are free electrons moving among the atoms. Book 1 Section 4.1 Conduction

26 Book 1 Section 4.1 ConductionCheck-point 1 – Q3 Mary heats three rods of the same size. Rods A : iron Rod B : copper Rod C : glass Which rod will heat up first? Book 1 Section 4.1 Conduction

27 3 Examples of conduction and insulationa Keeping warm Humans and animals keep warm by insulation. Air is a poor conductor of heat  Humans wear clothes that trap air  energy will be conducted away slowly Book 1 Section 4.1 Conduction

28 Book 1 Section 4.1 Conduction3 Examples of conduction and insulation b Feeling hot or cold when touching an object At the same temp, a metal surface feels colder than a wooden surface because… …metal conducts energy away from your hand more easily.  makes you feel colder Book 1 Section 4.1 Conduction

29 3 Examples of conduction and insulationc Cooking Cooking utensils are mainly made of metals effective heat transfer from stove to food Handles made of poor conductors (e.g. plastic, wood) insulating allow us to grasp with bare hand Book 1 Section 4.1 Conduction

30 Book 1 Section 4.1 Conduction4 Factors affecting the rate of conduction Factors enhancing the rate of conduction (from one end to the other): Larger temp difference Smaller distance between two ends Better conducting material Larger cross-sectional area Video 4.2 The Chinese clay pot Book 1 Section 4.1 Conduction

31 Book 1 Section 4.1 ConductionCheck-point 2 – Q1 Which of the following gives the main reason why woollen gloves keep us warm in cold winters? A Wool absorbs heat. B Wool is soft. C Wool traps air. D Wool is a good conductor. Book 1 Section 4.1 Conduction

32 Book 1 Section 4.1 ConductionCheck-point 2 – Q2 Which of the following explains why a tile floor feels colder than a wooden floor? A Tile is a better conductor than wood. B Wood is a better conductor than tile. Book 1 Section 4.1 Conduction

33 Book 1 Section 4.1 ConductionCheck-point 2 – Q3 Frying-pans are made of metal because it is a good ____________ of heat. Handles of frying-pans are made of wood because it is a good ____________ of heat. conductor insulator Book 1 Section 4.1 Conduction

34 Book 1 Section 4.1 ConductionThe End Book 1 Section 4.1 Conduction