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Shrillness of a sound is determined by the ______ of vibration.
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A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
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The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?
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Gurmit wanted to perform Activity 13.8 using a laser torch. Her teacher advised her not to do so. Can you explain the basis of the teacher’s advice?
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Explain how you can take care of your eyes.
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What are the different ways in which water gets contaminated?
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Why does the increased level of nutrients in the water affect the survival of aquatic organisms?
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Forests and coal are ______ natural resources.
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What steps would you suggest for the judicious use of fuels?
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Read the following terms and select the pair that is related to inheritance of characters.
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Green colour of leaves is due to presence of the pigment ______.
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The thread-like structures present in the nucleus are
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Read the following statement and write the appropriate term against the statement.
I transfer characters from parents to offsprings. Who am I? ...................
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Lila always eats only dal and rice in every meal. She often falls ill and has become prone to diseases. Can you suggest changes in her diet which can make her healthy and free from disease?
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A few of Paheli’s classmates eat potato chips and burgers regularly during the recess at school. Are they healthy eating habits? Give reasons.
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Given below are certain food items required for proper nourishment of adolescents. Name the nutrients present in the food items and write their functions.
| S. No. | Food items | Major Nutrient | Functions |
| 1. | Pulses and nuts | ||
| 2. | Oranges and Amla | ||
| 3. | Sugar, Roti | ||
| 4. | Oils | ||
| 5. | Vegetables |
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A water tank has four taps fixed at points A, B, C, D as shown in the following figure. The water will flow out at the same pressure from taps at
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A brick is kept in three different ways on a table as shown in the following figure. The pressure exerted by the brick on the table will be
 |
 |
 |
| A | B | C |
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A chapatti maker is a machine which converts balls of dough into chapatties. What effect of force comes into play in this process?
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It is difficult to cut cloth using a pair of scissors with blunt blades. Explain.
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