Form 4 Physics Chapter 4

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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 100OC. 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)

(b)

(c)

(a)

(b)

(c)

(d)

(e)

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

4 - 3 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 OC B. 0 OC C. -273 OC D. 100 OC

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 OC B. 65.4 OC C. 62.5 OC D. 57.7 OC

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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

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4 - 5 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 ?

15000 937.5 1 16 Pt C m



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 ₈₀0

4 - 6 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

4 - 7 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 toabsorb a large amount of heat due to its highspecific 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

4 - 8 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 o C 

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-10C-1]

A. 53 oC 

B. 60 oC C. 66 oC D. 70 oC

Plastic handle High specific heat capacity

Steel High specific heat capacity

4 - 9 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 SPECI FIC 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

(80)(3 60)

(49.2 6.4) 10







14400

42.8 10



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

4 - 12 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.

4 - 13 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-1oC-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 107 W

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

Q = (60%)(9.0 x 107 J) = 5.4 x 107 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-1oC-1

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

1. Use a cooling fan