1. HEAT ENERGY
19 May 2018
Physics 11

2. 6.0 Heat/Thermal Energy - EH
~Heat is a form of energy
~according to the KMT (Kinetic Molecular Theory) molecules have more EK (speed) when heated
~Heat is transferred btw 2 bodies of different temperatures
~transfer occurs via:
*conduction - collision of particles
-convection - movement of particles
-radiation - energy traveling as waves
eg) place a hot rock into cold water
The temperature of 2 objects in contact will equilibrate.
Disc 14 #27
19 May 2018
Physics 11

3. Heat as Energy
19 May 2018
Physics 11

4. Radiation
19 May 2018
Physics 11

5. 6.0 Heat/Thermal Energy - EH (cont’d)
~Temperature vs. Thermal Energy
Temperature: average energy of all particles in a sample
Thermal Energy: Total energy of all particles in a sample
19 May 2018
Physics 11

6. 6.1 Heat/Thermal Energy Transfer
-all substances have different abilities to gain or lose heat. (eg. Metal absorbs heat easier than rubber)
-We use the SPECIFIC HEAT CAPACITY (C) to describe a substance’s ability to absorb/conduct heat.
C= heat energy needed to change the temperature of 1.0 kg of a material by 1.0˚C.
Disc 14 #17-21
19 May 2018
Physics 11

7. 6.1 Heat/Thermal Energy Transfer (cont’d)
We can find the EH gained or lost with:
EH = mC∆T
NB - for water and most liquids
1mL = 1g
1L = 1000g = 1kg
1cm3 = 1mL
1cc = 1mL
EH = Heat Energy (J)
∆T = change in temperature (ºC)
m = mass (kg)
C = specific Heat Capacity (J/(kgºC))
Eg) How much heat is needed to raise the temperature of 100g of lead from 20 ºC to 33 ºC? (CL=130 J/kgoC)
EH = mC ∆T
= 0.100(130)(13)
= 169J
19 May 2018
Physics 11

8. 6.2 Efficiency
-a great deal of energy is lost during an energy transformation as HEAT
eg) burning fuel in car - start with fuel (1000J)
-900J lost in heat only 100 used to propel car
The percentage of energy actually used is EFFICIENCY
Show Snakey demo with a long spring
This will always be less than 100% (in the real world)
19 May 2018
Physics 11

9. Eg. A kettle rated at 2200 W is used to heat 1
Eg. A kettle rated at 2200 W is used to heat 1.2 L of water from 12 oC to 92 oC. If the kettle is 65% efficient, how long will it take to heat the water? (C=4180 J/kgoC)
19 May 2018
Physics 11

10. 6.3 Mixture Problems Conservation of Energy: heat lost = heat gained
NB - assume no heat escapes (but actually some does escape from the system)
Eg. #1 Consider the system to the right: If Cw=4180 J/kgoC and the final temperature = 16˚C Calculate cm.
NB - 1mL H20 = 1g H2O
19 May 2018
Physics 11

11. 6.3 Mixture Problems (cont’d)
heat gained by H20 = heat lost by metal
MWCW∆TW = MMCM ∆TM CM
19 May 2018
Physics 11

12. 6.3 Mixture Problems (cont’d)
Eg. #2 Mix 250mL coffee at 90°C with 50mL milk at 5°C.
Find final temperature. (Assume Cm=Cc)
MCCC∆TC = MmCm∆Tm
MCCC (90-T) = MMCM (T-5)
MC (90-T) = MM (T-5)
0.250 (90-T) = 0.050(T-5)
0.250(90)-0.250(T) = 0.050T-0.050(5)
(T) = 0.050T-0.250
= 0.050T T
= 0.30T
T = 75.8 oC
19 May 2018
Physics 11