SCIENCE TEACHERS ASSOCIATION OF NIGERIA UNIVERSITY OF LAGOS DEPARTMENT OF SCIENCE AND TECHNOLOGY

1. SCIENCE TEACHERS ASSOCIATION OF NIGERIA • UNIVERSITY OF LAGOS • DEPARTMENT OF SCIENCE AND TECHNOLOGY • 2012 NATIONAL PHYSICS SUBJECT PANEL WORKSHOP • HELD AT GOVERNMENT TECHNICAL COLLEGE , AGIDINGBI-IKEJA • DATE: TUESDAY 22ND MAY, 2012. • COURSE MODULE: PHY 303 • MODULE: THREE • UNIT: 2 • NAME OF RESOURSE PERSON: DR.S A ADEYEMO • LECTURE DELIVERED BY: DR. S A ADEYEMO(SENIOR LECTURER)

5. The Universe is made up of matter and energy. Matter is made up of atoms and molecules (groupings of atoms) and energy causes the atoms and molecules to always be in motion - either bumping into each other or vibrating back and forth. The motion of atoms and molecules creates a form of energy called heat or thermal energy which is present in all matter. Even in the coldest voids of space, matter still has a very small but still measurable amount of heat energy.

6. Energy can take on many forms and can change from one form to another. Many different types of energy can be converted into heat energy. Light, electrical, mechanical, chemical, nuclear, sound and thermal energy itself can each cause a substance to heat up by increasing the speed of its molecules. So, put energy into a system and it heats up, take energy away and it cools. For example, when we are cold, we can jump up and down to get warmer. • Here are just a few examples of various types of energy being converted into thermal energy (heat).

7. (1) Mechanical energy is converted into thermal energy whenever you bounce a ball. Each time the ball hits the ground, some of the energy of the ball's motion is converted into heating up the ball, causing it to slow down at each bounce. To see a demonstration of how this happens

9. A thermal infraredof a ball before (left) and after (right) being bounced image.

10. (2) Thermal energy can be transfered to other objects causing them to heat up. When you heat up a pan of water, the heat from the stove causes the molecules in the pan to vibrate faster causing the pan to heat up. The heat from the pan causes water molecules to move faster and heat up. So, when you heat something up, you are just making its molecules move faster.

11. (3) Electrical energy is converted into thermal energy when you use objects such as heating pads, electrical stove elements, toasters, hair dryers, or light bulbs

13. A thermal infrared image of a hair dryer and a flourescent light bulb.

14. (4) Chemical energy from the foods we eat is converted into heating our bodies. • (5) Light from the sun is converted to heat as the sun's rays warm the earth's surface. • (6) Energy from friction creates heat. For example when you rub your hands, sharpen a pencil, make a skid mark with your bike, or use the brakes on your car, friction generates heat

16. A thermal infrared image of a pencil after being sharpened (left) and of hot brakes in a car (right). Notice the hot tip of the pencil

17. There are many other examples. Can you think of some more? • The more energy that goes into a system, the more active its molecules are. The faster molecules move, the more heat or thermal energy they create. So, the amount of heat a substance has is determined by how fast its molecules are moving, which in turn depends on how much energy is put into it.

18. ACTIVITY: • Let students pretend to be molecules. First have them stand still and close together. Then have the students wiggle and then walk and move around to demonstrate more energy entering the system. Have them move faster and jump up and down as even more energy enters the system. Then have the students stop and notice where they are. They should be much farther apart and should feel much warmer than they were originally.

19. Heat can be transferred from one place to another by three methods: conduction in solids, convection of fluids (liquids or gases), and radiation through anything that will allow radiation to pass. The method used to transfer heat is usually the one that is the most efficient. If there is a temperature difference in a system, heat will always move from higher to lower temperatures.

20. CONDUCTION: • Conduction occurs when two object at different temperatures are in contact with each other. Heat flows from the warmer to the cooler object until they are both at the same temperature. Conduction is the movement of heat through a substance by the collision of molecules. At the place where the two object touch, the faster-moving molecules of the warmer object collide with the slower moving molecules of the cooler object. As they collide, the faster molecules give up some of their energy to the slower molecules. The slower molecules gain more thermal energy and collide with other molecules in the cooler object. This process continues until heat energy from the warmer object spreads throughout the cooler object. Some substances conduct heat more easily than others. Solids are better conductor than liquids and liquids are better conductor than gases. Metals are very good conductors of heat, while air is very poor conductor of heat. You experience heat transfer by conduction whenever you touch something that is hotter or colder than your skin e.g. when you wash your hands in warm or cold water.

21. A thermal infrared image of a coffee cup filled with a hot liquid. Notice the rings of color showing heat traveling from the hot liquid through the metal cup. You can see this in the metal spoon as well. This is a good example of conduction

22. CONVECTION: • In liquids and gases, convection is usually the most efficient way to transfer heat. Convection occurs when warmer areas of a liquid or gas rise to cooler areas in the liquid or gas. As this happens, cooler liquid or gas takes the place of the warmer areas which have risen higher. This cycle results in a continuous circulation pattern and heat is transferred to cooler areas. You see convection when you boil water in a pan. The bubbles of water that rise are the hotter parts of the water rising to the cooler area of water at the top of the pan. You have probably heard the expression "Hot air rises and cool air falls to take its place" - this is a description of convection in our atmosphere. Heat energy is transfered by the circulation of the air.

23. This thermal infrared image shows hot oil boiling in a pan. The oil is transfering heat out of the pan by convection. Notice the hot (yellow) centers of rising hot oil and the cooler outlines of the sinking oil..

24. RADIATION: • Both conduction and convection require matter to transfer heat. Radiation is a method of heat transfer that does not rely upon any contact between the heat source and the heated object. For example, we feel heat from the sun even though we are not touching it. Heat can be transmitted though empty space by thermal radiation. Thermal radiation (often called infrared radiation) is a type electromagnetic radiation (or light). Radiation is a form of energy transport consisting of electromagnetic waves traveling at the speed of light. No mass is exchanged and no medium is required.

25. A thermal infrared image of the center of our galaxy. This heat from numerous stars and interstellar clouds traveled about 24,000 light years (about 150,000,000,000,000,000 miles!) through space by radiation to reach our infrared telescopes.

26. The atoms and molecules in a substance do not always travel at the same speed. This means that there is a range of energy (the energy of motion) among the molecules. In a gas, for example, the molecules are traveling in random directions at a variety of speeds - some are fast and some are slow. • Temperature is a measure of the average heat or thermal energy of the particles in a substance. Since it is an average measurement, it does not depend on the number of particles in an object. In that sense it does not depend on the size of it. For example, the temperature of a small cup of boiling water is the same as the temperature of a large pot of boiling water. Even if the large pot is much bigger than the cup and has millions and millions more water molecules.

27. We experience temperature every day. When it is very hot outside or when we have a fever we feel hot and when it is snowing outside we feel cold. When we are boiling water, we wait for the water temperature to increase and when we make popsicles we wait for the liquid to become very cold and freeze.

29. Summary: Temperature is a measure of the average heat or thermal energy of the particles in a substance. Temperature does not depend on the size or type of object.

30. Many devices have been invented to accurately measure temperature. It all started with the establishment of a temperature scale. This scale transformed the measurement of temperature into meaningful numbers. • In the early years of the eighteenth century, Gabriel Fahrenheit (1686-1736) created the Fahrenheit scale. He set the freezing point of water at 32 degrees and the boiling point at 212 degrees. These two points formed the anchors for his scale. • Later in that century, around 1743, Anders Celsius (1701-1744) invented the Celsius scale. Using the same anchor points, he determined the freezing temperature for water to be 0 degree and the boiling temperature 100 degrees. The Celsius scale is known as a Universal System Unit. It is used throughout science and in most countries. • There is a limit to how cold something can be. The Kelvin scale is designed to go to zero at this minimum temperature. The relationships between the different temperature scales are: • oK = 273.15 + oCoC = (5/9)*(oF-32)        oF = (9/5)*oC+32

31. oF • oC • oK • Water boils • 212 • 100 • 373 • Room Temperature • 72 • 23 • 296 • Water Freezes • 32 • 0 • 273 • Absolute Zero • -460 • -273 • 0 • At a temperature of Absolute Zero there is no motion and no heat. Absolute zero is where all atomic and molecular motion stops and is the lowest temperature possible. Absolute Zero occurs at 0 degrees Kelvin or -273.15 degrees Celsius or at -460 degrees Fahrenheit. All objects emit thermal energy or heat unless they have a temperature of absolute zero. • If we want to understand what temperature means on the molecular level, we should remember that temperature is the average energy of the molecules that composes a

32. substance. The atoms and molecules in a substance do not always travel at the same speed. This means that there is a range of energy (the energy of motion) among the molecules. In a gas, for example, the molecules are traveling in random directions at a variety of speeds - some are fast and some are slow. Sometimes these molecules collide with each other. When this happens the higher speed molecule transfers some of its energy to the slower molecule causing the slower molecule to speed up and the faster molecule to slow down. If more energy is put into the system, the average speed of the molecules will increase and more thermal energy or heat will be produced. So, higher temperatures mean a substance has higher average molecular motion. We do not feel or detect a bunch of different temperatures for each molecule which has a different speed. What we measure as the temperature is always related to the average speed of the molecules in a system. So in a cold object the molecules move slowly and in a hot object the molecules move faster. And when two objects are in contact, thermal equilibrium is reached when all the molecules of both objects have the same average molecular motion. Which means the same speed. • Also, there are several types of temperature measuring devices and how they work:

33. The earliest form of thermometer, known as a thermoscope, was a liquid-in-glass thermometer that was open to the atmosphere and thus responded to pressure. By sealing a thermoscope so that it responded only to temperature, the modern form of a liquid-in-glass thermometer resulted. As a temperature sensor, its use dominated temperature measurement for at least 200 years. Liquid-in-glass thermometers had a profound effect on the development of thermometry and, in popular opinion; they are the only “real “thermometers! Liquid-in-glass thermometer sensors were developed in variety to fill nearly every nichein temperature measurement from –190C to +600C, including the measurement of temperature differences to a millikelvin

34. In spite of the fragile nature of glass, the popularity of these thermometers continues because of the chemical inertness of the glass, as well as the self-contained nature of the thermometer. Measurement sensor designers are unlikely to develop their own liquid-in-glass thermometers, but many will use them to check the performance of a new temperature sensor. The emphasis in this chapter section will therefore be on the use of mercury-in-glass thermometers — the most successful liquid-in-glass thermometer — as calibration references. Mercury-in-glass thermometers provide a stable temperature reference to an accuracy of 0.1C, provided they are chosen and used with care. The extra requirements to achieve higher accuracy are indicated, but are beyond the scope of this section. The trend is, however, to move away from mercury-in-glass thermometers for specialized uses (in particular, where the risk from glass or mercury contamination is not acceptable; for example, in the food or aviation industries). Other forms of temperature sensors described in this handbook are be more suitable.

35. General Description • A common form of mercury-in-glass is a solid-stem glass thermometer illustrated in the diagram below. The other major form of liquid-in-glass thermometer is the enclosed scale thermometer, for which the general principles discussed will also apply. There are four main parts to the liquid-in-glass thermometer:•The bulb is a thin glass container holding the bulk of the thermometric liquid. The glass must be of suitable type and properly annealed. The thinness is essential for good thermal contact with the medium being measured, but it can result in instabilities due to applied stress or sudden shock. Some lower-accuracy, general-purpose thermometers are made with a thicker glass bulb to lower the risk of breakage. •The stem is a glass capillary. Again, a suitable glass is necessary and may differ from that of the bulb. The bore can be gas-filled or vacuous. The volume of the bore must be somewhat smaller than the volume of the bulb for good sensitivity. In addition, the bore must be smooth, with a uniform cross section. • FIGURE 32.70 • The main features of a solid-stem glass thermometer. The thermometer can have an enlargement in the stem or an attachment at the end of the stem to assist in the positioning of the thermometer. Thermometers will display several of these features, but seldom all of them.

37. •The liquid is usually mercury for best precision, or an organic liquid for lower temperature ranges.•The markings are usually etched or printed onto the stem. The markings include the scale, toallow direct reading of the temperature, as well as other important information

38. A liquid-in-glass thermometer is widely used due to its accuracy for the temperature range -200 to 600°C. Compared to other thermometers, it is simple and no other equipment beyond the human eye is required. The LIG thermometer is one of the earliest thermometers. It has been used in medicine, metrology and industry. The first thermometer appeared around 1650 and was a development from the thermoscope. The liquid used was spirit from wine. By 1714, thermometers with mercury were found to give a more linear scale than spirits. By 1742, a centigrade scale using 100 steps from the point of boiling water to the melting point of water was suggested by Anders Celsius. • In the LIG thermometer the thermally sensitive element is a liquid contained in a graduated glass envelope. The principle used to measure temperature is that of the apparent thermal expansion of the liquid. It is the difference between the volumetric reversible thermal expansion of the liquid and its glass container that makes it possible to measure temperature.

39. The liquid-in-glass thermometer comprises: • - • a bulb, a reservoir in which the working liquid can expand or contract in volume • - • a stem, a glass tube containing a tiny capillary connected to the bulb and enlarged at the bottom into a bulb that is partially filled with a working liquid. The tube's bore is extremely small - less than 0.02 inch (0.5 millimetre) in diameter • - • a temperature scale is fixed or engraved on the stem supporting the capillary tube to indicate the range and the value of the temperature. It is the case for the precision thermometers whereas for the low accurate thermometers such as industrial thermometer, the scale is printed on a separate card and then protected from the environment. The liquid-in-glass thermometers is usually calibrated against a standard thermometer and at the melting point of water • - • a reference point, a calibration point, the most common being the ice point • - • a working liquid, usually mercury or alcohol • - • an inert gas is used for mercury intended to high temperature. The thermometer is filled with an inert gas such as argon or nitrogen above the mercury to reduce its volatilization. • The accuracy of measurement depends mainly on the extent of immersion of the thermometer into the medium - not just the bulb but also the stem. • There are three types of immersion, as shown in the following figure: total, partial and complete immersion, depending on the level of contact between the medium and the sensor.

41. An error can be produced when the thermometer is not immersed to the same extent as it was when it was originally calibrated. An 'emergent stem correction' may be necessary when it is not possible to immerse the thermometer sufficiently deeply. • The response of the thermometer depends on the bulb volume, bulb thickness, total weight and type of thermometer. To reduce the response time, the bulb should be small and the bulb wall thin. The sensitivity depends on the reversible thermal expansion of the liquid compared to the glass. The greater the fluid expansion, the more sensitive the thermometer. • Mercury was the liquid the most often used because of its good reaction time, repeatability, linear coefficient of expansion and large temperature range. But it is poisonous and so other working liquids are used. Common organic liquids are toluene, ethyl alcohol, pentane; their expansion is high but not linear and they are limited at high temperature. They need to be dyed, the most common colours being red, blue and green.s

42. The following table gives for each liquid the useable temperature range. • Working liquid • Temperature range (°C) • Mercury • -38 to 650 • Toluene • -90 to 100 • Ethyl alcohol • -110 to 100 • Pentane • -200 to 20 • THE LIQUID-IN GLASS THERMOMETER • Advantage • Disadvantage • no power source required • limited to applications where manual reading is acceptable, e.g. a household thermometer • repeatable, calibration does not drift • have a limited useable temperature range • easy to use & cheap • cannot be digitised or automated

43. The working principle of various thermometer • Infrared thermometer principle -- infrared temperature-measuring plan by optical system, photoelectric detector, signal amplifier and signal processing.  Mercury thermometer - is because mercury heat and cold water? Why don't, as for not, because the water in 4 degrees, heat bilges cold also, and mercury coefficient of expansion is larger, changes obviously also have filled alcohol is red that alcohol thermometer for measuring temperature (- 78 ~ + 110 degrees or so), mercury thermometer for lateral higher temperature (about 15 ~ 300 degrees).  Pressure type thermometer principle -- according to law, namely certain liquid expanding quality liquid, in its volume, under the condition of liquid pressure and temperature is linear. Gas, steam pressure and temperature is a certain function relation, and therefore the pressure gauge thermometer should be uniform type quintiles. Pressure type thermometer is by filling inductive medium temperature of temperature bag, transmitting pressure components (capillary) and pressure sensitive components (spring tubes) composition.  

44. Infrared thermometer principle -- infrared temperature-measuring plan by optical system, photoelectric detector, signal amplifier and signal processing. Display output components. Optical system gathering its field of view of the target ir radiation energy, infrared energy focus on the photo detector it converted to the corresponding signal, then through this signal conversion into target value being measured.

45. Thermocouple thermometer principle - thermocouple thermometer is principle will "meter. with - copper wire" series - clematis - into a loop, at both ends of the copper wire and joints, can form two "joint" (junction), if the two locations at different temperature of among them, can produce voltage, in micro ammeter can measure flows through the weak clematis and copper current. Thermocouple thermometer will be used, you must first below of calibration. A joint into ice water, put another joint in boiling water, write down when the current strength, this is the current value ℃temperature 100. For two known species of metallic conductors speaking, current with two joint is proportional to the temperature difference is very big, namely, measuring range by - 200 ℃ to 1,700 ℃, sensitivity high.

46. The working principle of thermocouple thermometer: When two kinds of different conductor contacts make return circuit, loop lieutenant general produces electromotive force, the size of this kind of electromotive force is direct with the temperature between two contact difference is concerned, this kind of phenomenon calls piezoelectricity effect. Using the feeling lukewarm component that piezoelectricity effect makes is thermocouple, using the thermometer that thermocouple comprises as feeling lukewarm component is thermocouple thermometer. In classic electron theory, piezoelectricity situation by electrometric temperature difference and osculatory electromotive force two parts are formed. Electrometric temperature difference is by what all pledge the difference of two upright temperature of conductor is caused. Contacting electromotive force is the conductor A that differs when two kinds and B contact when, because both free electron density is different, in the contact the dot produces an electron to diffuse, and formation electromotive force. Contact electromotive force not only the function that is temperature T, its are far also to the contribution of piezoelectricity situation bigger than electrometric temperature difference. Measure the piezoelectricity power that gives thermocouple to arise because of temperature change.

47. A thermometer comparison • Various types of temperature sensors are listed below. They are: • Mercury thermometer • Alcohol thermometer • Bimetallic thermometer * • Resistance thermometer • Thermocouple • Radiometer

48. Various thermometers are used in different situations. For instance, mercury thermometers are the standard equipment at surface weather stations, and bimetallic thermometers are used in radiosondes. Thermocouples are used for in situ observations at locations wired to a computer network. Radiometers are used for remote observations. • The table below compares the various thermometers.

49. Advantages • Mercury thermometer • Cheap • Durable • Accurate • Easily calibrated • disadvantages • cannot be used for thermograph • slow response • Dispay is harder to read  • Fragile •  does not work below -39C(hg freezing point • mercury vapour is poisonous

50. Alcohol thermometer (compared to a mercury thermometer) • advantages • lower freezing point (-114 �C) • Less hazardous • larger coefficient of expansion • disadvantages • alcohol can polymerise • fluid loss by evaporation hard to avoid