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Chapter 3

Change of state

Revision 
Internal Energy
- Kinetic Energy (Temperature)
- Potential Energy (Change of state)




冰工廠 (天文台 Hong Kong Observatory) - 冰雹的形成 (formation of Hail Stone)




State of boiling


How to prepare "spring egg"? 學是學非第42集
Three method was try out
  • boil at 65 for 25 minutes
  • put it in microwave oven
  • add salt and Vinegar in boiling water
Reason: Albumen and Yolk solidified at different temperature. (NOT the melting point)



Class work 1

Given: 
Specific latent heat of fusion of ice: 334000 J kg-1   
Specific heat capacity of water : 4200 J kg-1 oC-1  

1. a) How much energy is required to change 0.5kg of ice to water at 0oC?
    b) Find the energy required to chang 0.5kg of water from 0oC to 20oC.
    c) Find the total energy required to change 0.5kg of ice at 0oC to water at 20oC.
    d) If a 500W heater is used, how long will it take to complete the (c).

S.3 Physics Raz-kids ebook reading 2014
Recommended books
Level P (Magnetism)
Level R (Inventions)
Level S (Our Solar system)

Read 1 book and complete the quiz with 80% correct: 1 Bonus mark in E2
Read 2 or more books and complete the quiz with 80% correct: 2 bonus marks in E2

2nd Term UT: Chapter 3 ONLY


3.2 Evaporation

Liquid can change to vapour at temperature LOWER THAN the BOILING POINT. This is known as evaporation.

 Evaporation Boiling 
Temperature to occur  Occurs at any temperatureOccurs at its boiling point 
 Place to occur at the surface onlythrough the liquid 
 Any Bubbles formed? NO Bubbles AppearBubbles Appear 
 Energy Source From liquid itself or from the surroundingsFrom heat source (heater)  

Evaporation Absorb energy from surroundings, Temperatures decreases and produces cooling effect.

Factors affecting the rate of evaporation:
 Factors  weather 
 temperature of watertemperature increases Sunny  increase
 Surface area of water surface area increase  increase
 Density of vapor increasehumid decrease 
 Movement of vaporwith breeze  WIndy increase 

Condense more readily at lower temperatures. Latent heat is released

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