What is meant by thermal energy? Thermal energy is the energy that a substance contains due to the vibration of its atoms. If a substance is heated, its atoms vibrate faster. This may show a rise in temperature or may change to a state with higher energy.
Explain what happen to the internal energy when the body is heated?
When a body is heated, its internal energy will increase because its molecules will move faster.
What is the relation between the rise in temperature and the amount of heat gained by an object? The amount of heat gained by an object is given by H=m·c·(T2-T1). Where
(T2-T1) rise in temperature "C or K".
"m" the mass of the body "Kg"
"c" Specific heat capacity of material in J/KgK or J/KgC.
What are the factors that affects the thermal energy?
Temperature rise
The mass of the body
Specific heat capacity of material
What is meant by specific heat capacity? Specific heat capacity is the amount of heat energy required to raise the temperature of a "1" Kg of the substance by "1" degree Celsius. Its unit is given as J/KgK or J/KgC.
Describe the specific heat of water? The specific heat of water is high (4200 J/Kg).
Why creatures can to resist a high change in temperature? Because they contain a large amount of water.
What is meant by thermal capacity of a body?
Thermal capacity of a body is the amount of heat energy required to raise the temperature of the whole body by one Celsius degree.
Why water is used in central heating systems? Water is used in indoor heating systems to store and carry heat energy to heat radiators because it has a very large heat capacity.
Explain the process of heat exchange? When two objects at different temperatures are mixed they exchange energy until they reach a common temperature.
State the law of conservation of energy?
The amount of heat gained is equal to the amount of heat lost.
Problems
A piece of "Al" of mass 0.5 kg is heated to a 100ºC and then placed in a 0.4 Kg of water at 10ºC. If the final temperature of the mixture is 30ºC. What is the specific heat of Aluminum if the specific heat of water is 4200J/C. Heat gained by water=Heat Lost by Aluminum
mw·cw·(x-Tw)=mAl·cAl·(TA1-x)
0.4*4200*(30-10)=0.5*cAl*(100-30)
cAl=960 J/KgC
A tank holding 60 Kg of water is heated by a 3 KW electric heater. If the specific heat of water is 4200J/KgK estimate the time for the temperature to rise from 20C to 70C.
Heat Lost by heater=Heat gained water
Electrical Energy= Heat gained water
Power*time= mw*cw*(x-Tw)
3000*t=60 Kg* 4300 * (70-20)
t=4200 seconds= 70 minutes
