Book 1 (chapter 1: Temperature And Heat Transfer)

Question 1

What are fixed points?

Answer 1

Well-defined and reproducible temperature in the laboratory

Question 2

Two types of fixed point

Answer 2

1. Upper fixed point (steam point) (100 degree Celsius)
   = boiling point of pure water at standard atmospheric pressure (1 atm)
2. Lower fixed point (ice point) (0 degree Celsius)
   = melting point of pure ice at standard atmospheric pressure (1 atm)

(Not international standard used by scientist)

Question 3

Internal energy (definition)

Answer 3

Sum of molecular kinetic energy due to random motion and molecular potential energy.

Question 4

Heat (definition)

Answer 4

Energy transferred between two bodies due to temperature difference

Symbol: Q

Unit: J

Molecules collide with each other. Energy is transferred by collisions.

Question 5

Heat capacity (definition)

Answer 5

Energy required to change the temperature of an object by 1 degree Celsius

Question 6

Heat capacity (definition)

Answer 6

Energy required to change the temperature of an object by 1 degree Celsius

Question 7

Absolute zero (0K=-273degree celcius)

Answer 7

Particles freeze and do not move

Question 8

Relationship between the avg KE and temperature

Answer 8

When the molecules posses more kinetic energy and move more rapidly, the temperature of the body increases

Question 9

Two bodies at the same temperature

Answer 9

Same average molecular kinetic energy
BUT the one with larger mass has a higher internal energy

Question 10

Temperature (definition)

Answer 10

It is a measure of the average kinetic energy due to the random motion of the molecules in a body

Question 11

Relationship between internal energy AND temperature and mass

Answer 11

Since the internal energy of a body includes the total kinetic energy of all the molecules in the body. It increases with temperature and mass.

Question 12

Energy transfer

Answer 12

The larger the temperature difference, the higher the rate of energy transfer.

Heat flows from a high-temperature body to a low-temperature body

The energy transfer stops when they reach the same temperature (thermal equilibrium)

Question 13

How to increase internal energy of a body?

Answer 13

Increase the temperature through HEATING and DOING WORK

Question 14

Conduction (s,l,g) (have to be in contact)

Answer 14

Molecules vibrate (x move)
Heat conduct from warm to cold

Explanation: particles on the hotter end vibrate faster and hit neighbouring particles which then gain energy through collisions and vibrate faster. Energy is transferred from hotter to colder end by collisions of particles.

(Vacuum: no conduction)

The material which conducts heat fast is called thermal conductor (or conductor of heat)
The material which conducts heat slow is called thermal insulator (or insulator of heat)

Question 15

Why is metal a better thermal conductor than non-metal?

Answer 15

They have free electrons which can move freely and help transfer heat.

Question 16

How does loathes keep us warm?

Answer 16

The clothes trap air which is a good thermal insulator

Question 17

Why do you feel colder when you touch a metal plate when you touch a wooden plate?

Answer 17

Metal is a better thermal conductor and it transfers heat faster than wood.

Question 18

Why are most of the cookware made of metal?

Answer 18

Because metal is a good thermal conductor and transfers heat faster.

Question 19

Why some of the cookware is made of clay?

Answer 19

Because slay is a good insulator which can reduce heat loss and ensures more even heating.

Question 20

Why are the ice cubes at the bottom seem not to be letting while the surface on the surface is boiling?

Answer 20

Because water is a good thermal insulator and heat only transfers slowly to the bottom by conduction.

convection only occurs at the bottom

Question 21

Order of thermal conductivity

Answer 21

Solid > liquid > gas

Question 22

Convection (concepts)

Answer 22

Definition: it is a heat transfer process by means of movement of molecules within fluid (gas or liquid), that arises through difference in density.

Process: Water heats up, hot water rises and becomes less dense. Cold water sinks.

Convection does not happen in solid

Question 23

Examples and application of convection

Answer 23

1. Sea breeze
   Because the specific heat capacity of water is larger than land, in daytime, temperature of water is smaller than land and breeze from sea to land; while at night time, temperature of water is larger than land and breeze is from land to sea.
2. Heater and air-conditioner
   Air condition is set up high on the wall. It takes in the warm air and cools it. This facilitates the convection current.
   Heater is placed on the floor . It takes in the cold air and warm it, this facilitates the convection current.
3. The shapes of a candle flame
   Hot air rises, and cool air sinks.
4. Convection in the Earth (for geography ONLY)
5. Freezers in the supermarket
   Cold air sinks and remains in the freezer
6. Igloo
   Snow is a good thermal insulator and it traps a lot of air. It can reduce heat loss due to convection and conduction. Hot air is trapped inside the igloo.

Question 24

Prior knowledge of radiation

Answer 24

Why does black objects look black?
—> Black object absorbs all the light and reflect no light.

Why does white object looks white?
—> White object absorbs no light and reflect all light.

Why does red object look red?
—> Red object absorbs all light except red and reflect red light.

The 7 colours of the rainbow: red, orange, yellow, green, blue, indigo, violet

Question 25

Radiation (concept)

Answer 25

Every object emits radiation in all directions.
The hotter the object, the more infrared-red radiation it emits.
Everything is both an absorber and radiator/emitter of radiation.
A object colder than surrounding has a net gain of energy by radiation.
A object hotter than surrounding has a net loss of energy of radiation.

Question 26

Factors affecting the emission and absorption or radiation

Answer 26

1. Temperature: the higher the temperature, the more radiation it emits
2. Colour: Dull black surface is a good absorber and emitter of radiation. Black objects look black at room temperature. Shiny /white surfaces are poor absorber and radiator / emitter of radiation.
3. Surface area: the larger the surface area, the more radiation it emits.

Question 27

How to distinguish if something is related to conduction/convection/radiation?

Answer 27

Conduction: material
Convection: 👍🏻fan/👎🏻cap/cover
Radiation: colour
—> increase / decrease the heat transfer by ______________ (gain / loss)

Question 28

Applications of heat transfer

Answer 28

1. Vacuum flask
   Cap (traps the hot air inside (if hot liquid) —> reduce the heat transfer by convection
   Plastic cup (good thermal insulator —> reduce the heat loss by conduction)
   Silvered surfaces (silver is a poor absorber of radiation reduce heat transfer by radiation)
2. Pressure cooker
   Lid seals shut trapping steam inside (reduce heat loss by convection)
   Trapped s team builds pressure and raises cooking temperature (it has higher air pressure than outside)
   Higher pressure —> higher boiling point of water —> food is cooked at a higher temperature
3. Greenhouse
   Infra-red radiation cannot potassium through the glass
4. Summer and winter uniform
   In summer time, white is a poor absorber of radiation. In winter, dark grey i s a good absorber of radiation
5. Halogen lamp cooker
   Lid with fan and halogen bulb —> cook more evenly (more air flow)
6. Solar cooker

Question 29

Temperature (definition)

Answer 29

The measure of average molecular kinetic energy per molecule

Question 30

Molecular potential energy

Answer 30

The larger the distance between the molecules, the larger the potential energy

Question 31

Molecular potential energy

Answer 31

The larger the distance between the molecules, the larger the potential energy

Question 32

Why is the energy of 1kg ice smaller than 1kg water?

Answer 32

Their temperatures are the same and they have the same average kinetic energy. However, objects at liquid state larger potential energy than that in solid state. Water has a higher potential energy than ice. That’s why the internal energy of water is larger.

Question 33

Change in temperature vs change in state

Answer 33

When ice melts, the temperature remains the same