Please show all work with the math portions of the questions! Please try to summ

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Please show all work with the math portions of the questions! Please try to summarize the answers if they are short answer. Thank you!

Name Date Partners HoMEwoRK For LAB 3 HEAT ENERGY TRANSFER Based on your observations, which of the following seems to most accurately predict how fast heat energy is transferred from a hotter to a colder object? Explain the experimental basis for your answer a. the temperature of the hotter object 1. b. the temperature of the colder object c. the difference in temperature between the two objects The air temperature outside on a winter day is 10°C. Two identical outdoor swimming pools are heated by electric heaters. Swimming pool A is main tained at 20°C, while pool B is maintained at 30°C. Compare the rate at which heat energy is transferred to pool A with the rate at which heat energy is transferred to pool B. Be quantitative (give a ratio for the power ratings of the two heaters) and explain your answer in terms of your observations in this laboratory 2. Suppose that the outside temperature drops to 5°C. Now compare the new rate at which heat energy must be transferred to pool A to maintain it at 20°C to the rate in Question 2. Again be quantitative and explain your answer based on your observations in this lab 3. 4. Room temperature is 20°C. For what temperature of an object will there be no net heat energy transfer from the object to the room or from the room to the object? Explain your answer based on your observations in this lab If objects sitting in a room for a long time are all at the same temperature why do metal objects feel cooler to the touch than cloth or plastic ones? 5. 59 LAB 3: HEAT ENERGY TRANSFER 235

Explanation / Answer

1.C

Rate of heat transfer is proportional to temperature difference (Newton's law of cooling)

2. Heat energy needed Q= m*Cp*(T2-T1)

case A:

Q1= m*Cp*(30-10) = 20*m*Cp

case B

Q2 = m*Cp*(20-10) = 10*m*Cp

Q1/Q2 = 2 => pool A requires double the heat than B

if time required to heat both pool is same then, rate of heating of A should be double the rate heating of B

3. Qnew = m*Cp*(20-5) = 15*m*Cp (New rate of heating)

old rate of heating Qold= 20*m*Cp ( from 2nd question for case A)

Qnew/Qold = 15/20 = 3/4

4. Room temperature =20 oC

The object must be at room temperature (20 oC) for no net transfer of energy i.e temperature difference between object and surroundings should be zero

If temperature of object is > 20 oC , then cooling of object takes place

If temperature of object is < 20 oC, then heating of object takes place

5.

Metal is a good heat conductor

plastic and clothes are bad heat conductors compared to metals

Average human body temperature = 37 oC

average room temperature = 25 oC

When we touch metal, heat is transferred from our hand to metal i.e hands becomes colder. That's why we feel colder when we touch good heat conductors. And don't feel the same when we touch bad heat conductors

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