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Paperwork Mastering Physics Course # DRKIDD Has online book access Put up two assignments –Real & practice –Let me know if practice is useful –Other study areas appear useful.

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Schedule Short Term Today – Work out Exercise #2 Friday – Chapter 18 Lecture Monday – Off Tuesday – Lab #1 –Copyworks –Quiz#1 Wed HMWK due 11pm

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Problem Solving Ch. 17 Exercises –Toss in shark infested waters & see how you swim… –#1 of special interest to physics majors. Will let you work it out, ask for help if you like. –#2 – Lets do it now

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Temperature vs. Energy Plot

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Exercises 2. Heat transfer –How many grams of boiling gold would it take to boil 100 grams of water held at room temperature (say 300K)? –How much boiling water would it take to melt 10 grams of gold? –Lets Simplify Problem a little bit

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Exercises 2. Heat transfer –A. What is the least amount of molten gold that it would take to boil off 100 grams of water held at room temperature (say 300K)? The gold is at a temperature just above the melting point. –B. How much boiling water would it take to melt 10 grams of gold? –Now we dont have to find the heat capacity of molten gold…

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Equation? Equation relating Heat to Temp? Equation for relating heat to boiling/melt?

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What do we need to know? A. What is the least amount of molten gold that it would take to boil off 100 grams of water held at room temperature (say 300K)? The gold is at a temperature just above the melting point. What type of problem is this? What constants do we need? Heat capacity of gold ~ 0.1 J/(g K) Heat of fusion of gold ~ 65 J/g Melting Point of gold ~ 1300 K Heat capacity of water ~ 4 J/(g K) Heat of vaporization of water ~ 2000 J/g Notice it takes a lot more energy to raise the temperature of water than gold. Insight into different types of solids? Metals, Insulators, etc…

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Have Constants, Now What? A. What is the least amount of molten gold that it would take to boil off 100 grams of water held at room temperature (say 300K)? The gold is at a temperature just above the melting point. Determine what we know. Make Table of parameters. KnownUnknown GoldWaterGoldWater

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Have Constants, Now What? A. What is the least amount of molten gold that it would take to boil off 100 grams of water held at room temperature (say 300K)? The gold is at a temperature just above the melting point. Determine what we know. Make Table of parameters. KnownUnknown GoldWaterGoldWater MassMassHeat ConstantsConstantsHeat Initial TempInit. TempFinal TempFinal Temp Just from Problem itself What can we figure out fast?

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Have Constants, Now What? Determine what we know. Make Table of parameters. KnownUnknown GoldWaterGoldWater MassMassHeat ConstantsConstantsHeat Initial TempInit. TempFinal TempFinal Temp How does final temp of gold relate to water? How does change in heat for gold relate to water?

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Have Constants, Now What? Determine what we know. Make Table of parameters. KnownUnknown GoldWaterGoldWater MassMassHeat ConstantsConstantsHeat Initial TempInit. TempFinal TempFinal Temp How does final temp of gold relate to water? Both 100 o C How does change in heat for gold relate to water? Heat from Au = Heat into H 2 0

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Have Constants, Now What? Determine what we know. Make Table of parameters. KnownUnknown GoldWaterGoldWaterMass ConstantsConstantsHeat (Same for Both) Initial TempInit. TempFinal Temp How does final temp of gold relate to water? Both 100 o C How does change in heat for gold relate to water? Heat from Au = Heat into H 2 0 Two unknowns, need two equations. Notice we know everything about water…

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To Solve Determine what we know. Make Table of parameters. KnownUnknown GoldWaterGoldWaterMass ConstantsConstantsHeat (Same for Both) Initial TempInit. TempFinal Temp Know everything about H20. Heat into H20 = Heat to raise water from RT to 100oC + Heat of vapor. for 100g Have constants, plug in and solve

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To Solve Determine what we know. Make Table of parameters. KnownUnknown GoldWaterGoldWaterMass ConstantsConstantsHeat (Same for Both) Initial TempInit. TempFinal Temp Know everything about H20. Heat into H20 = Heat to raise water from RT to 100oC + Heat of vapor. for 100g Have constants, plug in and solve Set up similar equation for gold. Heat out of Au = Heat to fuse gold into a solid + heat to lower temp to 100 o C Mass is unknown variable, but have total heat (Same as found for H20)

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Part B How much boiling water would it take to melt 10 grams of gold? What is equilibrium temperature? Melting point of gold?

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Add some Calc Real materials, heat capacity not a constant. Depends on Temperature For gold say: c ~ ( T) J/(g K)

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Add some Calc c ~ ( T) J/(g K) If mass is equal to 10 grams, how much heat is needed to raise the temperature from 100 o C to 300 o C?

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Strategy c ~ ( T) J/(g K) If mass is equal to 10 grams, how much heat is needed to raise the temperature from 100 o C to 300 o C? Does m depend on T?

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Strategy c ~ ( T) J/(g K) If mass is equal to 10 grams, how much heat is needed to raise the temperature from 100 o C to 300 o C? Now what?

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Strategy c ~ ( T) J/(g K) If mass is equal to 10 grams, how much heat is needed to raise the temperature from 100 o C to 300 o C? Now integrate and be done with it.

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Strategy c ~ ( T) J/(g K) If mass is equal to 10 grams, how much heat is needed to raise the temperature from 100 o C to 300 o C? Now integrate and be done with it.

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Schedule Short Term Today – Work out Exercise #2 Friday – Chapter 18 Lecture Monday – Off Tuesday – Lab #1 –Copyworks –Quiz#1 Wed HMWK due 11pm

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