PEMUAIAN

THERMAL EXPANSION

By Mr Juwarto

www. juwarto.com

GAMES

Standard Competency:Understanding state of matter and their change

Basic competenceDoing experiment relate to expansion and apply in daily life.

Indicator to achieve competenceTo take simple experiment for showing expansion in solid, liquid and gas.

Find expansion process, in solid, liquid and gas.To show expansion in solid, liquid, gases, and their technology

GlossaryHeat = PanasHeated = dipanaskanCooled = didinginkanExpansion = PemuaianExpand = MemuaiContraction = penyusutanContract = MenyusutLinear expansion coefficient = Koefisien muai panjangArea expansion coefficient = Koefisien muai luasVolume expansion coefficient = Koefisien muai volume

Why a gap is given between rail roads?

Why bridge connectors are given a space?

ExpansionSolids will expand when it is heated and contract when it is cooled.

When heated, the atoms and molecules of the matter will vibrate faster than usual because of

the high temperature

Atoms and molecules need more space then the matter will expand to any

direction

Therefore

Expansion is INCREASE in size when an object is heated.

2. Area ExpansionA

ΔA

3. Volume Expansion

1. Linear Expansionl0

Δl

KINDS OF EXPANSION

Thermal Expansion

Expansion of solid

Expansion of liquid

Expansion of gas

Linear expansion

Area expansion

Volume expansion

Linear Expansion (pemuaian panjang)Influences by:1. Kinds of Solid2. The length of an object3. The change of Temperature

Linear Expansion coefficient (α)• is a value that states the rate of an expansion speed of

an object per temperature degree• The Higher linear expansion coefficient of an object is,

the faster the object will expand

lo

l

lt Tll o

lll ot

lt= Final length (m)lo= Initial length (m)Δl = length expansion (m)α= Linear expansion coefficient (/ C ˚)ΔT= Changes of temperature(C ˚)

Linear Expansion

Given : lo = 40 mT1 = 0 °CT2 = 100 °Cαsteel = 0.000011/C°

Question: ΔlAnswerΔl = α. lo . ΔT = 0.000011/C° . 40 m . 100 C°

= 1.1 x 10-5 .4 x 101 . 1 x 102 m = 4.4 x 10-2 m

= 0.044 m

Example 1:1. A steel railway track is 40 metres long at 0 °C. How long is its

expansion if it is heated up to 100 °C? (αsteel = 0.000011/C°)

ΔT = T2 -T1 = 100 C°

Example 2.A steel bridge is 100 m long at 20 °C. What is the final

length if its heated until 80 °C?(α steel is 0.000011/ C °)

Exercise1. A copper bar at 15°C is 20 metres long, then it is heated

up to 35°C. Determine how much its length will expand during the heating process if its expansion coefficient is 0.000017/ C°.

2. An iron bar at 20˚C is 3 meter long, and then it is heated up to 100˚C. Determine the final length of bar if linear expansion coefficient (α) is 0.000012/C˚?

3. A Pyrex glass with initial length of 5 meters is heated up 50Co from initial temperature. Determine the length expansion of that glass if its length expansion coefficient is 0.000004/C0.

4. The length of steel bar (α= 0.000012/C°) at temperature of 30°C is 50 cm. If the length of that steel bar becomes 50.011 cm, the temperature increase is

5. You’re heating a 2.5 m lead bar, coefficient of linear expansion 2.9 × 10–5 /C°, raising its temperature by 40C°. What is the final length of the bar?

1. What is expansion? Explain.2. Give 3 examples of expansion in daily life!3. When do the objects expand? Explain.4. Mention the factors that influence expansion!5. What kind of formula to find the changing of length of linear

expansion!6. What instrument do you use to find the linear expansion?7. The initial length of iron is 30 m at 25 ˚C. if it’s heated up to 90

˚C. Determine the length of iron after being heated. (linear expansion coefficient of iron is 0.000012 /C˚)!

Answer these questions correctly!

Area Expansion

AoA

At

A = x Ao xT

At = Ao +A

A = change in Area (m2) = Area expansion coefficient (/Co)Ao = Initial Area (m2)T = change in temperature (Co)

= 2 α

Volume Expansion

Vo V

VtV = Vo t

Vt = Vo + V

V = change in Volume (m3) = Volume expansion coefficient (/Co) Vo = Initial Volume (m3)T = change in temperature (Co)

For solid = 3 α All gas = /C°

THERMAL EXPANSION

LINEAR EXPANSION AREA EXPANSION VOLUME EXPANSION

For solid For solid

For Gas

A0

ΔA V0

l0

ΔlΔV

Tll o TAA o TVV o

lll ot AAA ot VVV ot

2 3

C2731

1. A plate of glass measures 100 m long and 50 m wide at 20 oC. What is its final area if the temperature is increasing until 70oC? (α = 0.9 x 10-5/C°)

2. A 200 cm3 Alcohol is heated from 25oC to 75 oC. Calculate the volume expansion of alcohol if volume expansion coefficient of alcohol is 0.0012 /Co.

3. Volume of kerosene at 5oC is 2 liter. If its heated until 105oC, how much the final volume of kerosene? (ɤ of kerosene is 0.000955 /Co).

4. The volume of glass cylinder at 10 oC is 1 liter. It’s full with alcohol. How much the spilled alcohol if it heated until 60 oC? (α glass = 0.000009/Co ; ɤ alcohol = 0.00120 /Co )

(spilled = tumpah)

Problems of Volume Expansion :

1. Bimetallic strip Bonding two metals with dissimilar thermal expansion coefficients

What will happen if we heated bimetallic strip? Bimetallic will bend to metal with the smallest linear expansion coefficient Example:

Bimetallic strip which consist from brass and steel. Bimetallic strips will bend to steel direction, because:

α brass = 1.9 x 10-5/C° α steel = 1. 1x 10-5/C° α brass > α steel

The examples of the use of expansion or contraction in daily life

α copper > α iron

Bimetallic strips will bend to iron direction

HEATED

CONCLUSION: Bimetallic strips will bend to metal with the smallest linear expansion coefficient

Bimetallic strips can be found on…

T-Bimetal ThermometerThermostat Automatic switch in an electric ironFire Alarm

Automatic switch

FIRE ALARM

PLAY

The examples of the use of expansion or contraction in daily life

2. Thermometer

3. Metal plates riveting (Pengelingan pelat logam)4. Installation of metal rims on wheels

(Pemasangan bingkai logam pada roda)

5. Railway track joint (Sambungan rel kereta api)6. Expansion joint on a bridge (Celah pemuaian pada logam)

The relationship between temperature and volume at

constant pressure

2

2

1

1

TV

TV

If a gas has a constant mass and is held at a constant pressure then the volume divided by the temperature is a constant value.

Note:V1 = Initial VolumeV2 = Final volumeT1 = Initial Temperature (Kelvin)T2 = Final Temperature (Kelvin)

Example :Problems of Charles’s Law1. The initial volume of a gas in piston is 100 cm3 and its

temperature is 327°C. If the volume decrease until 50 cm3 while the pressure is constant, temperature of gas will become…Given :V1 = 100 cm3 V2 = 50 cm3 T1 = 327 °CQuestion : T2 = ??Answer : First, Convert Temperature into Kelvin scale:

T1 = (327+273) K = 600 K

2

2

1

1

TV

TV

2

33 cm50K600cm100

T

KT 600cm50cm100 32

3

KKT 300cm100600cm503

3

2

T2 = (300-273) °C = 27 °C

1. Gas volume at temperature of 27°C is 20 liters. If gas is heated in constant pressure, the volume of the gas when its temperature 127°C is….

2. A 250 cm3 sample of neon is collected at 47 oC.   Assuming the pressure remains constant, what would be the volume of the neon at 207 oC?

3. The initial volume of gas in a piston is 400 cm3 and its temperature is 600 K. If half of the gas volume is reduced at the constant pressure, its temperature is…

Problems of Charles’s Law

Water anomaly (The anomolous expansion of water )

Most substances expand when heated and contract when its cooled, but water is unusual4°C 0°C (cooled) the water will expands0°C 4°C (heated) the water will contracts

Beside that range of temperature, water will experience normal expansion.

This phenomenon makes water have the smallest volume at temperature of 4°C

Thus, water will have the biggest density at 4°C

What is the benefit of water anomalous?

The anomalous expansion of water helps preserve aquatic life during very cold weather.

When temperature falls, the top layer of water in a pond contracts, becomes denser and sinks to the bottom. A circulation is thus set up until the entire water in the pond reaches its maximum density at 4°C. If the temperature falls further, the top layer expands and remains on the top till it freezes. Thus even though the upper layer are frozen the water near the bottom is at 4°C and the fishes etc. can survive in it easily.