Physics 21-24
4) In a heat engine driven by ocean temperature differences, the heat source (water near the surface) is at 293 K and the heat sink ( deeper water) is at 283 K. Calculate the ideal efficiency of the engine.
(293 K-283 K)/(293 K)= 0.034
2) Calculate the ideal efficiency of a ship's boiler when steam comes out at 530 K, pushes through a steam turbine, and exits into a condenser that is kept at 390 K by circulating seawater.
(530 K-390 K)/(530 K)= 0.45
1) Calculate the ideal efficiency of a heat engine that takes in energy at 800 K and expels heat to a reservoir at 300 K.
(800 K-300 K)/(800 K)= o.63
Terrestrial Radiation
Energy that the earth radiates.
3) Calculate the ideal efficiency of a steam turbine that has a hot reservoir at 112 C high-pressure steam and a sink at 27 C.
112 C+ 273= 384 27+ 273= 300 (384 K-300 K)/(384 K)= 0.22
5) What mass of water will give up 40 calories when its temperature drops from 80 C to 68 C.?
240 cal=(A) x (1 cal/g C) x (12 C) 240 cal= A x 12cal/g A=20 g
6) When a 50-gram piece of aluminum at 100 C is placed in water, it loses 735 calories of heat while cooling to 30 C. Calculate the specific heat capacity of the aluminum.
735 cal=(50 g) x (B) X (70 C) 735 cal= (3500 g C) x B 0.21 cal/g C= B
Thermostat
A practical application of a bimetallic strip.
Thermal Equilibrium
After objects in thermal contact with each other reach the same temperature, no heat flows between them.
Doppler Effect
An observed change in the frequency of a wave when the source or observer is moving
Radiant Energy
Energy transmitted by radiation.
Conduction
Heat transferred through the metal.
Newton's law of cooling
If an object is cooler than its surroundings, its rate of warming up is also proportional to change in T. Frozen food will warm up faster in a warm room than in a cold room.
Relative Humidity
Indicates how much water vapor is in the air compared to the limit that can be held for the temperature.
Conductors
Materials that conduct heat well.
Insulators
Materials that delay the transfer of heat.
Saturated
Max amount of water that can be held.
Condensation
Phase change from gas to liquid.
Evaporation
Phase change from liquid to gas.
Boiling
Phase change from liquid to gas. Gas forms beneath the surface of the water forming bubbles and are buoyed up.
Freezing
Phase change from liquid to solid.
3) A 30-gram piece of iron is heated to 100 C and then dropped into cool water where the iron's temperature drops to 30 C. How many calories does it lose to the water? (The specific heat capacity of iron is 0.11 Cal/g C.)
Q= (30 g) x (0.11 cal/g) x (70 C)= 231 cal
1) Calculate the number of calories of heat needed to change 500 grams of water by 50 celsius degrees.
Q= (500 g) x (1 cal/g C) x ( 50 C)=25,000 cal
2) Calculate the number of calories given off by 500 grams of water cooling from 50 C to 20 C.
Q= (500 g) x (1 cal/g C) x (30 C)= 15,000 cal
3) Calculate the energy needed to melt 100 grams of 0 C ice and then it to 30 C.
Q=(100 g) x (80 cal/g)= 8,000 cal Q= (100 g) x (1 cal/g) x (30 C)= 3,000 cal 8,000 cal + 3,000 cal= 11,000 cal
1) Calculate the energy (in calories) absorbed by 20 grams of water that warms from 30 C to 90 C.
Q=(20 g) x (1 cal/g C) x (60 C) = 1,200 cal
5) Calculate the energy released by 20 grams of 100 C steam that condenses and then cools to 0 C.
Q=(20 g) x (540 cal/g)= 10,800 cal Q=(20 g) x (1 cal/g C) x (100 C)= 2,000 cal 10,800 cal+ 2,000 cal= 12,800 cal
4) Calculate the energy absorbed by 20 grams of 100 C water that is turned into 100 C steam.
Q=(20 g)(540 cal/g)= 10,800 cal
2) Calculate the energy needed to melt 50 grams of 0 C ice.
Q=(50 g) x (80 cal/g)= 4,000 cal
4) Suppose the same 30-gram piece of iron is dropped into another container of water and gives off 165 calories in cooling. Calculate the iron's temperature change.
Q=165 cal/[(30 g)x(0.11 cal/g C)= 50 C
Quantity of heat energy required for change of phase= (mass) x (heat of fusion or heat of vaporization), or in equation form Q=mL. Heat of fusion=80cal/g; heat of vaporization=540 cal/g
Quantity of heat energy responsible for a temperature change= (mass) x (specific heat) x (change in temperature), or in equation form, Q=mcT.
Heat
The energy that transfers from one object to another because of a temperature difference between them.
Internal Energy
The grand total of all energies inside a substance.
Specific Heat Capacity
The quantity of heat required to raise the temperature of a unit mass of the substance from 0 to 1.
Thermal Contact
When heat flows from one object or substance to another it is in contact with, the objects or substances.
Regulation
When ice is under pressure and melts, but when the pressure is reduced to freezes back up.
Equilibrium
When the evaporation and condensation are in a state of balance, canceling effects. Evaporation exceeds condensation, liquid is cooled. Condensation exceeds evaporation, liquid is warmer.
Greenhouse Effect
When trapped sun warmth is hotter than it is around.
Convection
Where heating occurs by currents in a fluid.