haihongyuan.com

# Temperature and Heat.ppt

Temperature and Heat
The concept of temperature, measuring temperature, quantity of heat, heat capacity, latent heat, heat transfer

Temperature
Temperature is a measure of hotness or coldness of a body. Kelvin (K)
http://www.xqcd.net 摆线减速机 摆线针轮减速机 行星摆线减速机 http://www.u51688.com http://www.qiwhy.com

syllabus
S.I. unit:

Celsius scale
(Practical Scale)
LORD KELVIN

Intro video
click once

The current working temperature scale is the International Temperature Scale of 1990 (ITS-90) and is measured in degrees Celsius (°C)

Temperature (in degree Celsius) = Temperature in Kelvin – 273.15

Note:

0o C 100o C

= 273.15 K = 373.15 K

Ref:http://astronomy.swin.edu.au/cms/imagedb/album s/userpics/kelvin1.gif

2

Thermometers
Thermometers measure temperature.

Note: 1. Temperature is a number which gives the degree of hotness of a body on a chosen scale. (degree at which heating has occurred). 2. When we measure temperature we measure a thermometric property. 3. Two different thermometers do not necessarily give the same reading at the same temperature. Different Thermometric properties vary differently with temperature
3

Thermometric properties

Any physical property that changes measurably with temperature.

Examples

1. Length of column of Liquid. 2. Electrical resistance. 3. EMF of a Thermocouple Thermometer. 4. Colour. 5. Pressure of a gas at constant volume 6. Volume of gas at constant pressure
http://en.wikipedia.org/wiki/File:Charles_and_Gay-Lussac%27s_Law_animated.gif

click for More… info

4

Standard Thermometer

Celsius Scale for given thermometric property
? A temperature scale is needed with two fixed points (normally the freezing and boiling point of water) ? A thermometric property is needed, such as the length of a column of liquid in a glass tube

Measuring Temperature
(Alcohol-in-glass thermometer As School standard) ?Use un-graduated thermometer. ?Place in pure melting ice, mark position = l0 (0 on celsius scale) ?Place in steam above pure boiling water, mark position = l100 (100 on celsius scale)

5

Measuring Temperature

1. The length is taken at 0o C (in melting ice) = l0 2. The length is taken at 100o C (in boiling water) = l100 3. A graph of temperature versus length is plotted 4. Any temperature can then be read from the graph = lθ
SOLUTIONS CH 14 Exercises Folens

6

CALIBRATION CURVE OF A THERMOMETER USING THE LABORATORY MERCURY THERMOMETER AS A STANDARD

Expt “Write up”

Ref: Physics Experiments (Heat) pages 4&5

7

Practical Thermometers
Science Technology Society - Temperature
? clinical thermometers Mercury in glass with constriction thermometers. Infra-red radiation thermometer.

? oven thermometers boiler thermometers temperature gauge in a car.
Thermometers

8

HEAT
HEAT & TEMPERATURE

syllabus

Heat is a form of energy

Energy is measured in Joules (J)

States of

Matter

Matter exists in three states and transfers from one state to the other when heat is absorbed or released

Heat is a form of energy. If a cold object is immersed in hot water, heat will be transformed from the hot water to the cold object. The property which determines the direction of the heat from one body to another is temperature.

MELTING

EVAPORATION

SOLID
FREEZING

LIQUID

GAS

CONDENSATION

Energy absorbed Energy released
9

Quantity of Heat

The heat capacity of a substance is the energy needed to change its temperature by 1 K (1 0C)

Unit: Joule per Kelvin (J K-1) Heat (Q) = Heat Capacity (C) x Change in Temperature (??)

Q = C ??

Unit: Joule per kilogram per Kelvin J kg-1 K-1

Specific Heat Capacity (c): This is the amount of heat energy required to change the temperature of one kilogram of the substance by one Kelvin.
Mass (m) x specific Heat Capacity Change in temperature (??)

Heat energy(Q) = (c) x (lost or gained)

Q = m c ??
note: C=mc C = Heat capacity m = mass, c = Specific Heat 10

Capacity

The Latent Heat (L) of a substance is the heat energy needed to change the state of a substance without a change in temperature
Unit = Joule J

Heat change without change in Temperature

perspiration

The specific Latent Heat of Fusion is the amount of heat energy required to change 1kg of the substance from a solid to a liquid, without changing its temperature
Unit: Joule per kilogram (J kg-1)

The specific Latent Heat of Vaporisation is the amount of heat energy required to change 1kg of the substance from a liquid to a gas, without changing its temperature
Unit: Joule per kilogram (J kg-1)
11

Latent Heat - formula

Heat energy needed to change state: Heat (Q) = mass (m) x latent heat (L) ____________________________ Specific Latent Heat of Fusion of ice - formula
Example (ice ?water) Energy gained by ice = Energy lost by water + calorimeter

Q = heat energy; m = mass; L = latent heat of fusion or vaporization Unit: = Joule per kilogram J Kg-1

mice x Lfusion + mice x Cwater x ??(Rise) = mwater x Cwater x ??(Fall) + mcal x Ccopper x ??(Fall)
----------------------------------------------------------------------------------------------------------------------------- --

Specific Latent Heat of Vaporisation of Water - formula Example (water ?steam) Specific Latent Heat of Vaporisation of Water
SOLUTIONS CH 15 Exercises Folens

Energy lost by steam = Energy gained by water + calorimeter

msteam x Lvapour + msteam x Cwater x ??(Fall) = mwater x Cwater x ??(Rise) + mcal x Ccopper x ??(Rise)
12

Temperature and Heat energy
Graph: shows how temperature changes as heat energy is supplied.
Plateau region shows phase change. Heat is taken in or given out without change in temperature

gas 4 5

1. Cice = 2.108 kJ/kg/K 2. Lf = 334 kJ/kg 3. Cwater = 4.187 kJ/kg/K 2 solid 1

liquid 3

4. Lv = 2270 kJ/kg
5. Cvapour = 1.996 kJ/kg/K Note: latent heat values are
much higher

Ref: http://www.sei.i

13

To measure the Specific Heat Capacity of Water

Expt “Write up”
Ref: Physics Experiments (Heat) pages 8&9

14

Calculating the Latent Heat of Fusion of Ice

Expt “Write up”

Ref: Physics Experiments (Heat) pages 12&13

15

To measure the Specific Latent Heat of Vaporisation of Water

Expt “Write up”

Ref: Physics Experiments (Heat) pages 14&15

16

JOHN TYNDALL

Heat Transfer

The Archimedes Heat Ray – myth or reality?

Heat is transferred from place to place by: ? Conduction

The transfer of heat energy from molecule to molecule in a solid by the vibration of the molecules. There is no overall movement of the substance

? Convection
Convection is the transfer of heat through a liquid or gas by means of circulating currents of the fluid