Announcements Applied Physics 02-14-08 Temperature & Heat Florence Henderson (74) One new quiz up today. Get to work on them NOW! We will be burning food in lab on Tuesday. You may want to wear clothes that can get soot on them. Homework Problems: 5.11, 5.18, 5.22, 5.26, 5.29 Questions Are there any? Temperature A method to determine thermal equilibrium. A definition requires looking at matter on an atomic level. Temperature is a measure of the average KE of the molecules of a substance. Two objects with the same temperature have molecules with the same average KE. KE is transfered between objects through collisions.
Q01 Each molecule of a diatomic gas has mass m1. The gas is at temperature T. A second gas is monatomic and each atom has a mass of m2 = 2 x m1. A)The diatomic molecules are moving twice as fast as the monatomic atoms. B)The diatomic molecules are moving half as fast as the monatomic atoms. C)The diatomic molecules are moving slower, but more than half as fast, than the monatomic atoms. D)The diatomic molecules are moving faster, but not quite twice as fast, than the monatomic atoms. Daniel Gabriel Fahrenheit Scales Invented alcohol thermometer (1709) and mercury thermometer (1714) and: Proposed the Fahrenheit temperature scale (1724). Historically 0o F was the temperature of an equal mixture of salt and ice. Historically 100o F was the temperature of the human body. Modern Scale sets 32 o F as the melting point of water and 212 o F as the boiling point; normally body temperature ~98.6 o F Anders Celsius (Swedish Astronomer) Proposed a version of the celsius temperature scale in 1742. His version had 0 o C as the boiling point of water and 100 o C as its freezing point. Modern Scale sets 0 o C as the melting point of water and 100 o C as the boiling point. Step size on the Celsius scale is larger than the step size on the Fahrenheit scale. Celsius scale is the standard throughout science and most of the world. T(o C) = (5/9)[T( o F) - 32 o ] Average body temp ~ 37 o C -40 o F = -40 o C Other Scales Thermal Expansion As average KE increases, things tend to get larger! The expansion is generally linear Coefficient of Linear Expansion " Units 1/o C
Q02 What is the original length (Lo) of the mercury column? Express your answer in cm. Q03 What is the temperature change in the mercury? Express your answer in o C. Q04 What is the linear expansion coefficient for mercury? Express your answer in 1/ o C.
Q05 What is the change in the length of the mercury column? Express your answer in cm. Lo = 3.00 cm!t = 40.0 o C - 37.0 o C = 3.0 o C " = 60 x 10-6 1/ o C!L = (3.00 cm)(60 x 10-6 1/ o C)(3.0 o C) = 5.4 x 10-4 cm D = mass/volume Units gm/cm3 Units kg/m3 1kg 1m = 1000gm 3 (100cm) 3 = Density 1000gm gm = 10 3 1, 000, 000cm3 cm 3 1 kg gm = 10 3 m3 cm 3 Heat Thermal Energy (Internal Energy) This is related to Temperature (remember the relation to average KE). Heat will flow from a hotter object (higher temperature) to a cooler object (lower temperature). In two objects that are at the same Temperature, heat flow between them is equal.
Calculating Heat Flow Specific Heat Q = s m #T Q is heat m is mass #T is the change in the temperature s: is the specific heat There is a table of s s on page 108 (Table 5.3). Water has a relatively high specific heat. Water is a good storer of heat energy. Example Problems. A 50 gm substance loses 23 calories of heat energy when the temperature falls from 35 C to 20 C. What is the specific heat of the substance? m = 50 gm Q = 23 cal!t = 35 C - 20 C = 15 C 23 cal = s (50 gm)(15 C) s = (23 cal)/[(50 gm)(15 C)] s = 3.07x10-2 cal/(gm C) Q06 What is the mass in this equation, for this particular problem. Express your answer in gm s. Q07 What is the specific heat for this particular problem. Express your answer in cal/(gm o C).
Q08 What is the temperature change for this particular problem. Express your answer in o C. Q09 How much heat goes into the water? Express your answer in cal. m = 150 gm s = 1.0 cal/(gm C)!T = 3 C Q = [1.0 cal/(gm C)](150 gm)(3 C) Q = (450 cal)