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Subject: science-physics
Class: class VII
Key Concepts
types of heat, transfer of heat, measurement of heat, unit of heat, heat and its effects on air, heat and its effects on various materials
essential questions
1. Why do you think we needed to find a way to measure heat?
2. Why do you think there are two types of thermometers to measure temperature?
3. Have you ever wondered why mercury has been used to show the change in temperature in a thermometer?
4. How does transfer of heat happens between states of matter?
5. How do we get heat from the sun?
6. Why is our sense of touch not reliable for measuring heat?
Remembering:

  1. How do you define temperature?
  2. What are the various modes of transfer of heat?
  3. Fill in the :

a) the hotness of an object is determined by its_____

b) Temperature of boiling water cannot be measured by ____ thermometer.

c)Temperature is measured in degree_____

 

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understanding:

  1. Write the difference between clinical and laboratory thermometer.
  2. Can you pin point the reason why mercury does not drops suddenly in a clinical thermometer when taken out of the mouth?
  3.  Write in detail the experiment which shows convection mode of transfer of heat? Draw a labeled diagram.
  4. Write the difference between land and sea breeze. 
  5. What is the difference between heat and temperature?

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Application:

1. Why do we prefer light colored clothes in summers?

2. How will you read 35° C and 3/5 on a clinical thermometer?

3. Why is 37º C called average body temperature of human body?

4. If Boojho  wants to measure water temperature what type of thermometer will he use? Give reasons.

5. Why do we not use a lab thermometer for measuring body temperature?

6. In places of hot climate it is advised that outer walls of the houses be painted white. Explain.

7. Why are buildings in cold climate use hollow bricks for construction?

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Analysis:

  1. Wrap a thin paper strip tightly around an iron rod, when you try to burn the paper with candle while rotating the iron rod continuously it does  not burn . Point out the reasons for the same.
  2.  Mercury is used in thermometer to measure temperature change. Can you think of a reason why the level of mercury changes when brought in contact with another object?
  3.   a) When the Bunsen burner is lit, what happens to the rod just above it?    b) Which pin or paperclip dropped off the metal rod first? The one closest to or furthest from the Bunsen burner?   c) What does this tell us about the way in which heat is conducted along the rod?
  4. Why does the temperature of the body increases even when it is not in direct contact of heat producing object?

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Evaluation:

  1. Imagine that your teacher has been given a heater and an air-conditioning unit for your classroom. The heater will warm your classroom in winter and the air-conditioner will keep you cool in summer. You need to help you teacher decide where each item should go in the classroom. Should they go on the wall near the ceiling or near the floor? Should they go next to a window? Justify your answers.

 

2. When you light a candle and place it in a holder. First hold you hand above the candle. Then hold your hand on the side of the candle. Answer the following questions.

a) We know now that heat from a candle will be transferred to the air around it. These will warm up. Where will this air move to? Give reasons.

b) So, when you hold your hand above the candle, what do you feel and why? But, what about when you hold your hand on the side of the candle? Could you also feel warmth from the candle?

c) This is not convection as the air particles do not travel sideways when they warm up from the flame. So, how is energy transferred to your hand when you feel the warmth on the side of the candle?

d) Lastly,  a metal spoon in the candle flame and you felt the end, how would it feel after a little while? give reasons.

 

3. 

a) What happens to the smoke from the paper? Why do you think the smoke moves in this way? Justify your answers.

4. Take two similar transparent glass bottles having wide mouths. Put a few crystals of potassium permanganate or pour a few drops of in in one bottle. Fill this bottle with hot water. fill the outer bottle with cold water. cover the cold water bottle with a thick piece of paper such as a postcard. Press the postcard firmly with one hand and hold the bottle with the other hand. Invert the bottle and place it on top of the hot water bottle. Hold the bottles firmly. Ask some other person to pull the postcard. Observe what happens.

a) Why does ink move from hot water to cold water?

b) Why did hot water rise and cold water sink?

a) Write down the materials in order of how fast they conducted heat from the quickest to the slowest.

b) Why does the Vaseline melt?

c) Why do you think it was necessary to place the piece of cardboard or paper on the tripod stand underneath the metal rods. Hint: The tripod stand is also made of metal.

d) Why do you think it is necessary to use the same amount of Vaseline on the ends of each rod?

e)Do you think we could have performed this investigation if our rods were of different lengths? Why?

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Create:
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