CBSE Class 7 Science Physics Chemistry Biology Worksheet Set 02

PHYSICS

Question 1. Define the terms: a) TIME PERIOD b) OSCILLATION C) AMPLITUDE
Answer: a) Time Period: The time taken by a pendulum to complete one full oscillation is called its time period. Its SI unit is seconds.
b) Oscillation: To and fro or back and forth motion of an object about its mean position is called an oscillation.
c) Amplitude: The maximum displacement of a vibrating body from its mean position is called amplitude.
In simple words: Time period is time for one shake, oscillation is one complete swing, and amplitude is how far the swing goes from the center.

Exam Tip: Always include SI units (seconds for time period, meters for amplitude) when defining physical quantities to secure full marks.

Question 2. What is the time period of a seconds pendulum?
Answer: The time period of a seconds pendulum is exactly 2 seconds (it takes 1 second to move from one extreme position to the other and 1 second to return).
In simple words: A seconds pendulum takes 2 seconds to complete one full back-and-forth swing.

Exam Tip: Remember that a "seconds pendulum" refers to a pendulum with a period of 2 seconds, not 1 second.

Question 3. A pendulum completes one oscillation in 1.5 second what is the time period of the pendulum?
Answer: Time taken to complete one oscillation = 1.5 seconds
By definition, the time taken to complete one oscillation is called the time period.
Therefore, the time period of the pendulum = 1.5 seconds.
In simple words: The time period is simply the time taken for one full swing, which is given as 1.5 seconds.

Exam Tip: Do not confuse the number of oscillations with time period; 1 oscillation time directly equals the time period.

Question 4. Name an instrument which is used to produce sound in the laboratory?
Answer: A tuning fork is the instrument commonly used in the laboratory to produce sound of a fixed frequency.
In simple words: A metal tuning fork produces a clear sound when struck against a rubber pad.

Exam Tip: Mentioning a tuning fork along with a rubber pad demonstrates practical knowledge of physics laboratory equipment.

Question 5. What are the conditions necessary for hearing sound?
Answer: The necessary conditions for hearing sound are:
1. Presence of a vibrating body (source of sound).
2. Presence of a material medium (solid, liquid, or gas) for the propagation of sound.
3. A functioning hearing organ (ear) to receive the sound waves.
In simple words: You need something to make a sound, a medium like air to carry it, and ears to hear it.

Question 6. We cannot hear on moon, why?
Answer: Sound requires a material medium to travel from one place to another. The Moon has no atmosphere (it is a vacuum). Since there is no medium like air on the Moon for sound waves to propagate, sound cannot travel, and we cannot hear on the Moon.
In simple words: There is no air on the moon to carry sound waves, so sound cannot travel.

Exam Tip: Always highlight the absence of an atmosphere or vacuum as the primary reason why sound cannot propagate in space.

CHEMISTRY

Question 1. Label the marked parts of the diagram given below.
Answer: Based on the standard laboratory preparation of carbon dioxide setup shown in the diagram:
1. Thistle funnel
2. Confluent flask (or Round-bottom flask)
3. Delivery tube
4. Gas jar
5. Calcium carbonate (Reactant inside the flask)
In simple words: The labels identify the thistle funnel, flask containing reactants, delivery tube, and the gas jar collecting the gas.

Question 2. By which method is the gas collected in the gas jar?
Answer: Carbon dioxide gas is collected by the upward displacement of air (downward delivery) because it is heavier than air.
In simple words: Since carbon dioxide is heavier than air, it pushes the air upwards out of the gas jar and settles at the bottom.

Exam Tip: Note that CO\(_2\) cannot be collected over water efficiently because it is moderately soluble in water.

Question 3. Write the balanced equation for the laboratory preparation of carbon dioxide.
Answer: \(\text{CaCO}_3(s) + 2\text{HCl}(aq) \rightarrow \text{CaCl}_2(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)\)
In simple words: Calcium carbonate reacts with hydrochloric acid to produce calcium chloride, water, and carbon dioxide gas.

Question 1. a.Identify the given algae. b. What is obtained from this alga?
Answer: a. The given alga is Spirogyra (or Volvox, represented by the filamentous/colonial algal structure in typical textbooks).
b. Algae are primary producers used to obtain products like agar-agar, iodine, algin, and carrageenan, and are also used as a source of single-cell protein, vitamins, and biofuels.
In simple words: The image shows Spirogyra, which is useful for producing various biochemicals and serving as food/fertilizer.

Question 2. Which fungi is used for the production of citric acid in soft drink industry?
Answer: The fungus Aspergillus niger is widely used for the commercial production of citric acid used in soft drinks and food products.
In simple words: Aspergillus niger is a fungus that helps manufacture citric acid for tangy drinks.

Question 3. What happens during the formation of curd?
Answer: During the formation of curd, the bacterium Lactobacillus multiplies in milk and converts lactose (milk sugar) into lactic acid. This lactic acid causes milk proteins (casein) to coagulate, turning milk into semi-solid curd.
In simple words: Bacteria change milk sugar into acid, making the milk thicken into curd.