Saturday, 26 July 2014

Physics lessons

FIRST 2 WEEKS 

Physics 

Q1: Are both of the items ( Metal , book )  of the same temperature ?
Q2: Why does the metal feel much colder to touch then the book?
Q3: List the factors that affect the transfer rate of thermal energy.

Answers for Group A:

Q1: Yes. Both of them are kept in the same place.
Q2: Metal has free electrons and the atoms in it move faster, thus our hands lose more thermal energy  to the metal and we feel colder to touch.
       The book has no free electrons and atoms in it move slower, thus out hands lose less thermal energy to the book and feel less colder to touch than the metal.
Q3: 1- Temperature of objects 2- Type of materials 3- State of objects. 4- Temperature of surroundings. 5- Difference in Temperature 6-Humidity
Question: 
Liquid in Thermometer moves to 170mm on steam point and 20mm on freezing point of pure water. What is the temperature if the liquid in the thermometer moves to 50mm?

Answer: 20 Degrees Celsius 


THINK 1: 
Why do you feel cold when you enter an air-condition room after work on a hot day?

Group's Answer ( on showme) is lost.

THINK 2: 
Why do you shiver when you come out of the swimming pool on a hot day?



Question 2 Group Answer:
When we come out of the swimming pool, the water on our body gains thermal energy and evaporates. Our body loses thermal energy to the water. As we lose thermal energy, we shiver so that our body molecules can move faster and we will gain thermal energy back.

Individual Answer:
When we come out of the swimming pool,some water from the swimming pool will remain on our body. The water will gain Thermal Energy from our body and evaporates, taking the thermal energy away. As the water takes the thermal energy away, we will feel cold and it is a natural occurrence to shiver when we lose too much thermal energy. 

Think 3


Think 3 Answer :

Think 4

Group's Answer:


Below is the correct answer. 



Notice the gradient of the graph is very steep for the first few minutes but become less steep afterwards. Then, it will be constant after it reaches thermal equilibrium. 

Answer For THINK 4

The styrofoam cup is the outer cup as it is a poor conductor of heat and reduces the flow of thermal energy between the room and the water. Thus, the room will only make a little effect on the experiment. 
The inner cup is made of metal because metal is a good conductor of heat. This will help the experiment as thermal energy from the warm water will be transferred to the cold water faster. This will also mean that the cold water can gain thermal energy faster and the warm water can lose thermal energy faster. 

Flow of thermal energy between 2 objects depends very much on the temperature difference. The larger the temperature difference, the higher the flow of thermal energy and thus, the steeper gradient. As time goes by, the temperature difference gets smaller, the less flow of thermal energy, thus the less steeper the gradient is. This explains why the gradient is much steeper at the beginning. 

Lastly, the gradient is constant after a few minutes as there is no flow of thermal energy, reaching thermal equilibrium. 



NOTES:
EXPANSION AND CONTRACTION 






Notes for Physics Lesson 


Notes for Physics Lesson