Temperature

Physics 202Professor Lee

CarknerLecture 12

PAL # 11 Doppler

b)Detector toward, Source toward:f’ = f ( v+vD / v-vS )

for vD = 3 m/s, f’ higher

d) Detector away, Source toward:

f’ = f ( v-vD / v-vS )

for vD = 3 m/s, f’=f

c) Detector away, Source away:f’ = f ( v-vD / v+vS )

for vD = 3 m/s, f’ lower

e) Detector toward, Source away:

f’ = f ( v+vD / v+vS )

for vD = 3 m/s, f’=f

Thermodynamics

Thermodynamics deals with the internal energy of a system

We will examine how this internal energy changes due to changes in heat and work

One of the important concepts in thermodynamics is temperature

How do we experience temperature?

Thermoscope Changes in temperature cause changes in other

properties

We can measure these changes to construct a thermoscope, a device to record changes in temperature

The oven is at a higher temperature than the refrigerator Temperature changes are caused by an exchange of

heat

A Thermoscope

Thermal Equilibrium When the thermoscope stops changing, it

and the water are in thermal equilibrium

If we move the thermoscope to a different cup and it reads the same value we know that it and the second cup are also in thermal equilibrium

Zeroth Law of Thermodynamics

What happens if we pour the two cups together? The cups are in thermodynamic equilibrium

with each other

If two objects are each in thermal

equilibrium with a third object then they are also in thermal equilibrium with each

other

How Thermal

Equilibrium Works

Thermometers

In order for a thermoscope to be a thermometer if needs to be calibrated

For example, the Celsius scale

Them put the tube in boiling water and mark that mercury level “100”

You now have a Celsius thermometer

The Kelvin Scale

The Kelvin scale is designed so that 0 K is at absolute zero and that 273.15 K is at the freezing point of water

TC = TK -273.15

The Triple Point of Water

The triple point of water is the only temperature where water can exist in liquid, solid and gas forms simultaneously

Converting Temperatures

A temperature change of 5 Celsius degrees is equal to a temperature change of 9 Fahrenheit degrees

Temperature Scales

Gabriel Daniel Fahrenheit invented the mercury thermometer in 1714

Anders Celsius introduced his scale is 1742

William Thomson, Lord Kelvin, determined from theory that minus 273.15 degrees Celsius is the coldest it can get

Three Temperature Scales

What’s Hot, What’s Not

Thermal Expansion Some objects expand more than

others when heated

The degree of expansion depends on the change in temperature and the coefficient of expansion

Thermal Expansion of Ruler

Linear Expansion The degree to which the length of an object

changes is given by:L = L T

This applies to all dimensions of a solid length,

width and height

Two strips of metal with different coefficients of linear expansion attached together

This principle is used in dial thermometers and thermostats

Bimetal Strip

Volume Expansion If the linear dimensions of a solid change

then the volume must change:

Where =3

Density in general decreases with increasing temperature

Temperature and Heat

Temperature is a measure of the internal (thermal) energy of a system

Heat (Q) is energy transferred between systems due to a temperature difference

Heat can manifest itself in different ways

Being “hot” does not mean you have a lot of “heat”

Heat

The rate of heat exchange depends on the temperature difference Run warm water over your hands after being

outside on a cold day and the water feels hot

You feel hot on a hot day because your body generates heat and can’t get rid of it quickly enough

What is Heat?

Heat Units Heat is a form of energy and so its SI

unit is the joule (kg m2/s2) A joule is fairly small so sometimes the

kilojoule (kJ) is used

1 calorie is the heat needed to raise the temperature of 1 gram of water 1 deg C