Heat Capacity

 

1.    If an object is in the path of a "beam" of energy, say from the sun, depending upon the object's molecular structure and color it will take the energy in and convert it to internal molecular vibrations (internal energy).

 

2.    Any object will emit energy at the expense of its internal energy. 

 

Applications:

 

In terms of the visible portion of the sun's energy, objects that appear black take in all of the incident energy and white objects reflect (do not take in) most of the energy.  Applying (1) above, which object would be warmer?

 

At night, when no energy is being received from the sun, what would happen to the temperature of the surface of the earth, and why, according to (2) above.

 

In reality, both (1) and (2) are happening simultaneously, most of the time.  Describe why temperatures rise during the day and cool at night.

 

3.    In reality, solid objects, because of their molecular structure, take in a given amount of energy from the sun and convert it to internal energy much more efficiently than water.  They also lose energy more efficiently. Of the solid objects, metals do this very efficiently.The Specific Heat Capacity is defined as the ratio of the energy (calories) required to be absorbed (radiated) by one gram of a given susbstance to produce a 1oC temperature rise (fall). In the SI system of units it is defined as the number of Joules required to change the temperature of 1 kg of a substance 1oC.

 

Specific Heat Capacity (cp) = q/T

or

 

T =( 1/cp) q

For example, a gram of pure metal like silver would warm up 10oC upon absorbing 1 calorie of energy, but a gram of water would warm up only 1oC upon absorbing the same 1 calorie of energy.
Note: 1 calorie = 4.186 joules (both are units of heat (energy)

 

Substance

cp (per gram)

(cal/gram/ °C)

cp (per kg) (MKS)

(J/kg/ °C)

water (pure)

1.00

4186
wet mud 0.60 2512
Ice (0 °C) 0.50 2093
sandy clay 0.33 1381
dry air (sea level) 0.24 1005
quartz sand 0.19 795
granite 0.19 794
silver 0.10 419

 

 

 

Application:

 

At night, would temperatures fall more near a body of water or on the continent and why?

 

During the winter, would temperatures fall more on the continent or over the ocean and why?