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प्रश्न
Take a sheet of paper. Draw a spiral on it as shown in Figure. Cut out the paper along the line. Suspend the paper as shown in Figure above a lighted candle. Observe what happens. Think of an explanation.
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उत्तर
Here is the observation and explanation for the given activity:
Observation: When you cut out the spiral from the paper and suspend it above a lighted candle, the spiral begins to rotate.
Explanation: The heat from the candle flame warms the air around it, causing it to rise. This rising warm air creates a convection current. When the paper spiral is placed above the candle, the rising warm air hits the spiral and causes it to spin. This is because the moving air applies a force to the spiral, making it rotate.
संबंधित प्रश्न
Look at Figure. Mark where the heat is being transferred by conduction, by convection and by radiation.
A wooden spoon is dipped in a cup of ice cream. Its other end ______.
Write true or false for a given statement.
Medium is necessary for the transfer of heat by radiation.
Write true or false for a given statement.
Liquids are heated by conduction and radiation.
Fill in the blank
Heat transfer in liquids and gases is by ________.
Explain briefly the process of heat transfer by radiation.
What are the modes of heat transfer?
Match the items in column-I to the items in column-II
| Column-I | Column-II | ||
| 1. | Linear expansion | (a) | change in volume |
| 2. | Superficial expansion | (b) | hot body to cold body |
| 3. | Cubical expansion | (c) | 1.381 X 10-23 JK-1 |
| 4. | Cubical expansion | (d) | change in length |
| 5. | Boltzmann constant | (e) | change in area |
Heat is the transfer of energy between two objects at different temperatures.
Take two similar transparent glass bottles having wide mouths. Put a few crystals of potassium permanganate or pour a few drops of ink in one bottle. Fill this bottle with hot water. Fill the other 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 both the bottles firmly. Ask some other person to pull the postcard. Observe what happens. Explain.
