4.0 heat

Physics Module Form 4 Chapter 4 - Heat GCKL 2011

4 - 1

4 UNDERSTANDING THERMAL EQUILIBRIUM

What is

thermal

equilibrium ?

1. ( Heat, Temperature ) is a form of energy that flows from a hot body to a cold

body.

2. The SI unit for ( heat , temperature) is Joule, J.

3. ( Heat , Temperature ) is the degree of hotness of a body

4. The SI unit for (heat , temperature) is Kelvin, K.

5. When thermal equilibrium is reached, the net rate of heat flow between the two

bodies is (zero, equal)

6. There is no net flow of heat between two objects that are in thermal equilibrium.

Two objects in thermal equilibrium have the …same… temperature irrespective

of shape, mass, size or type of surface.

Calibration of

thermometer

7. The thermometric property of an object is important in the construction of a

thermometer. It is a physical quantity which is sensitive to and changes linearly

with the change in temperature of the object.

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8. Lower fixed point (l 0 )/ ice point : the temperature of pure melting ice/00C

9. Upper fixed point( l 100)/steam point: the temperature of steam from water that

is boiling under standard atmospheric pressure /1000C

10. The lengths of the mercury column in the mercury-in-glass thermometer is 2.6 cm

at 0OC and 22.6 cm at 100

OC. When the thermometer is placed in hot water, the

length of the mercury column is 16.9 cm. Calculate the temperature of the hot

water.

Liquid-in-glass

thermometer

11. The liquid used in glass thermometer should

(a) Be easily seen

(b) Expand and contract rapidly over a wide range of temperature

(c) Not stick to the glass wall of the capillary tube

12. List the characteristic of mercury

(a) Opaque liquid

(b) Does not stick to the glass

(c) Expands uniformly when heated

(d) Freezing point -390C

(e) Boiling point 3570C

13. Which modification increases the sensitivity of the thermometer ?

A. Increasing the size of the bulb

B. Increasing the thickness of the bulb

C. Reducing the diameter of the capillary tube

D. Reducing the length of the capillary tube


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Check Yourself 1

1. The diagram below shows a thermometer is

used to measure the temperature of hot water.

When the thermometer and the hot water are in

thermal equilibrium, which of the following is

not correct ?

A. The temperature of hot water is equal to the

temperature of the thermometer

B. No heat flow between thermometer and hot

water

C. Heat flows from hot water to thermometer

D. Heat flows from thermometer to hot water

2. Which of the following characteristics does a

liquid-in-glass thermometer work ?

A. Volume of a fixed mass of liquid

B. Length of the liquid

C. Resistance of the liquid

D. Pressure of the liquid

3. Which of the following temperatures

corresponds to zero on the Kelvin scale ?

A. 273 O

C

B. 0 O

C

C. -273 O

C

D. 100 O

C

4. Diagram below shows the liquid levels from

the bulb in three thermometers P, Q and R at

certain temperatures.

What is the temperature reading at

thermometer R ?

A. 70.8 O

C

B. 65.4 O

C

C. 62.5 O

C

D. 57.7 O

C


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4 UNDERSTANDING SPECIFIC HEAT CAPACITY

Definition of Heat Capacity

1. Quantity of heat energy required to raise the temperature of an object by

10C.

2. The unit of heat capacity is J0C-1

3. Beaker A has (greater, same, less) heat capacity than beaker B.

4. This means that the (bigger, smaller) the mass, the (larger, smaller) the

amount of heat stored.

Definition of Specific Heat

Capacity

1. Quantity of heat energy required to raise the temperature of 1 kg of a

substance by 10C.

2. The unit of specific heat capacity is Jkg-1 0C-1

3. An object with low specific heat capacity can be heated up quickly, as it

requires less heat to increase its temperature by 10C. It can be cooled quickly

due to little amount of heat stored in it.

4. An object with high specific heat capacity takes longer time to heat up, as it

requires more heat to increase its temperature by 10C. It is harder to cool

down due to larger amount of heat stored in it.

Q = Pt

Pt = mc

Q = Heat supplied

P = Power of heater

T = Time in seconds

M = mass of substance

C = Specific heat capacity

= Increase in

temperature

4.2

A

A

B

A


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Determining the heat capacity

of aluminium block

1. The purpose of wrapping the aluminium blok with wool heat loss to or

absorption of heat from the surrounding.

2. Oil in the holes for housing thermometer and the immersion heater is to

improve the conduction of heat from the heater to the thermometer through

the aluminium block.

3. The immersion heater of 50 W rated power is used for 5 minutes to heat up

the aluminium block. If the mass of the alumimium block is 1.0 kg and the

rise in temperature is 160C, what is the specific heat capacity of aluminium ?

15000937.5

1 16

PtC

m

Jkg-10C-1

4. Specific heat capacity calculated is usually larger than the standard value

because some heat is lost to the surroundings.

Aim To investigate the relationship between temperature rise and mass of water

Experiment

Hypothesis When the mass of water …increases… the temperature rise will …decrease….

Manipulated variable Mass of water

Responding variable Rise in temperature

Fixed variable Heating duration, water, weighing scale, power rating of heater used

Apparatus Thermometer, water, beaker water, weighing scale

Setup

800C 600C 800C 400C


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Procedure

1. 100 ml of water is placed in a 500 ml beaker.

2. A heater is placed in the water.

3. Heating process is carried out for 1minute.

4. Highest temperature achieved is recorded.

5. Step 2 to 4 is repeated for 200ml, 300ml, 400ml and 500ml of water.

Analysis

Volume of

water used,

V (ml)

Final

temperature,

T2 (0C)

Initial

temperature,

T1 (0C)

Rise in

temperature,

= T2 – T1

(0C)

1/ (0C-1)

100

200

300

400

500

Conclusion

V

1/

Applications of specific heat capacity

Water as heating agent in

heating radiator


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Water as a coolant in car

engine

Sea Breeze

(wind from the sea)

Land Breeze (wind from the

land)

2. Hot air rises up

from the land

1. During the day

land gets hotter

than the sea

because c land < c sea

3. Cold water will be

recirculated to repeat

the process continously

1. Cool water is pumped into the hot

water reservoir to absorb a large amount

of heat due to its high specific heat capacity.

1. Cool water is pumped

into the hot engine

3. Cool water is recirculated

through the engine blocks

and the process continues

while the engine is running

2. High specific heat

capacity of water allows it

to absorb a large amount of

heat from the engine

2. hot air rises

from the sea

2. Heat from hot water is

released to the cooler

surroundings of a room to

achieve thermal equilibrium

4. Hot water is

cooled by the

air from the

cooling fins

and the fan

3. Cool air

blows from

the sea to

replace the

space left by

the hot air

and

convection

currents in

the air are formed

3. Cooler

air blows

from the

land to

replace the

space left

by the hot

air and

convection

currents in

the air are

formed.

1. During the

night, the sea

is hotter than

the land

because

c land < c sea


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Household apparatus and

utensils

Check Yourself 1

1. Table below shows four types of liquid with

their respective specific heat capacities and

boiling points. All the liquids have the same

mass and same temperatures of 30oC. If the

same amount of heat is supplied to them,

which liquid, A, B, C or D will boil first ?

Liquid Specific heat

capacity (Jkg-10C-1) Boiling point

(oC)

A 3.0 50

B 5.0 80

C 4.2 100

D 0.2 200

2. Table below shows the specific heat capacity

of four different metals.

Which of the following is the most suitable

metal to be used in a rice cooker for fast

heating ?

A. P

B. Q

C. R

D. S

3. Diagram below shows a bullet moving at a

velocity of 60 ms-1

is embedded in a wooden

block.

Assuming all the energy lost by the bullet is

converted to heat energy and is absorbed by

the bullet. What is the rise in temperature of

the bullet ? ( Specific heat capacity of the

bullet = 120 Jkg-10C-1)

A. 0.5 oC

B. 2.0 oC

C. 30.0 oC

D. 60.0 oC

4. Diagram below shows 200 g of water at 0 oC is

poured into a cup containing 400 g of water at

80 oC . Assuming there is no heat loss to the

surroundings.

What is the final temperature of the mixture ?

[ Specific heat capacity of water = 4200 Jkg-10

C-1]

A. 53 oC

B. 60 oC

C. 66 oC

D. 70 oC

Plastic handle High specific heat capacity

Steel High specific heat

capacity


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5. Diagram below

shows the

temperature-

time graph of

two solids X

and Y of equal

mass but of

different substances are heated

simultaneously by identical heaters.

Which of the following comparison is correct?

A. Cx > Cy

B. Cx < Cy

C. Cx = Cy


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4 UNDERSTANDING SPECIFIC LATENT HEAT

Definition of

Latent Heat

1. Latent Heat is the total energy absorbed or released when a substance changes its physical

state completely at a constant temperature.

2. Latent Heat of fusion is heat absorbed when solid changes into liquid or heat released when

liquid changes into solid at constant temperature.

3. Latent Heat of vaporization is heat absorbed when liquid changes into vapour or heat

released when vapour changes into liquid at constant temperature.

4. Unit for latent heat is Joule (J).

5. Process in which solid directly changes into vapour is called sublimation.

Definition of

Specific

Latent Heat

1. Specific Latent Heat of fusion is heat absorbed when1 kgsolid changes into liquid or heat

released when liquid changes into solid at constant temperature.

2. Specific Latent Heat of vaporization is heat absorbed when1 kgliquid changes into vapour or

heat released when vapour changes into liquid at constant temperature.

3. Unit for latent heat is Jkg-1

.

4. When temperature remain constant, kinetic energy of the molecules remain constant.

However energy absorbed is used to overcome forces of attraction and atmospheric pressure.

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Heating curve Fill the empty boxes for the heating curve below with the following words

Calculation

of specific

latent heat of

fusion

1. Calculate energy supplied by the heater.

Q = Pt = (80)(3x60) = 14400 J

2. What is the mass of ice melted due to the heat absorbed from the surroundings?6.4 g

3. Determine the specific latent heat of fusion of ice.

L = m

Pt=

3

(80)(3 60)

(49.2 6.4) 10

=

3

14400

42.8 10= 3.364×10

5Jkg

-1

Solid, liquid, gas, boiling point, melting point,

latent heat of fusion, latent heat of vaporization

Mass of water collected in Set A = 49.2 g

Mass of water collected in Set B = 6.4 g

Power of heater = 80 W

Time interval of switching on the heater = 3 minutes


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Check Yourself 1

1. Diagram below shows the cooling curve of a

Gas. Temperatures T1 and T2 represents

T1 T2

A. Solidification Room temperature

B. Boiling Point Solidification point

C. MeltingPoint Freezing Point

D. Melting Point Room temperature

2. Diagram below shows the heating curve of a

solid Y of mass 2 kg which is heated by a

heater of 70 W power. Which statement

below is NOT true ?

A. Specific latent heat of Y is 10500 Jkg-1

.

B. Specific heat capacity of solid Y and

liquid Y are the same

C. Total heat used is 1120 J

D. Melting point of Y is 10oC

3. Diagram below shows the arrangement of

apparatus used to determine the specific latent

heat of vaporization of water. The water in the

beaker is heated by an immersion heater with a

power of 1 kW. The beaker and its content is

resting on an electronic balance which

measures the mass of the beaker and its

content.

When the water is boiling, it is found that 80 g

of water is boiled away in 3 minutes.

What is the specific latent heat of vaporization

of water ?

A. 2.10 x 106 Jkg

-1

B. 2.15 x 106 Jkg

-1

C. 2.20 x 106 Jkg

-1

D. 2.25 x 106 Jkg

-1

4. Diagram below shows the arrangement of

apparatus used to determine the specific latent

heat of fusion of ice. There are two identical

sets. One of the sets is called a control set

which is without a power supply.

The aim of the control set is


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A. To find the mass of ice melted due to the

heat absorbed from the surroundings

B. To find the mass of water formed by

condensation from the vapour in the air

C. To detect any changes in the melting point

of the ice

D. To find the mass of water evaporated

5.

Heat produced in an engine block of car needs to be transferred out promptly to prevent overheating. This is

done by circulating a suitable cooling liquid through the engine block.

(a) What is meant by ‘specific heat capacity of water is 4200 Jkg-1o

C-1

?

4200 J of heat is required to raise the temperature of 1 kg of water by 1oC.

(b) Based on the table above,

(i) Explain the suitable characteristics of the cooling liquid to extract heat out of an engine block.

High Specific Heat Capacity More heat can be extracted from the engine

High specific latent heat of

vaporization

More heat can be extracted from the engine

High boiling point Do not vaporize fast and cause unnecessary pressure to engine

Low rusting rate Engine can last longer

(ii) Decide which liquid is the most suitable and give reasons for your choice.

Liquid B, high specific heat capacity, high specific latent heat of vaporization, high boiling point and

low rusting rate.

(c) Total energy released by an engine in 1 hour = 9.0 x 107 J

Energy breakdown : mechanical 40% and heat 60%

Mass of cooling liquid circulating in 1 hour = 150 kg

Temperature of water entering the engine = 30oC

Temperature of water exiting the engine = 60oC

Based on the information above,

(i) Calculate the power of the engine

P = 9.0 x 107 J/3600 s = 2.5 x 10

7 W

(ii) Calculate the amount of heat produced by the engine in one hour.

Q = (60%)(9.0 x 107 J) = 5.4 x 10

7 J

(iii) Calculate the specific heat capacity of the cooling liquid.

Q = mc

5.4 x 107 J= 150(c)(60-30)

c = 12,000 Jkg-1o

C-1


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(d) Suggest two ways to dissipate the heat from the cooling liquid.

1. Use a cooling fan

2. Increase the surface area of the cooling coil

4.0 heat

Education

heat flows

heat gckl

conduction of heat

heat capacity1

unit of heat capacity

definition of specific

unit of specific heat

quantity of heat energy