CBSE Class 7 Science Physics Chemistry Biology Worksheet Set 01

PHYSICS

Question 1. A SONAR receives a strong echo of ultrasonic signal it sent downwards into the sea 3.6 seconds after the transmission. Calculate the depth of the sea-bed if the speed of ultrasonic waves in sea-water is 1250 m/s.
Answer: Time taken for the echo to be received (\(t\)) = 3.6 seconds
Speed of ultrasonic waves (\(v\)) = 1250 m/s
Total distance traveled by the wave (down and back up) = \(v \times t\)
Distance = \(1250 \times 3.6 = 4500 \text{ m}\)
Depth of the sea-bed (\(d\)) = \(\frac{\text{Total distance}}{2}\)
\(d = \frac{4500}{2} = 2250 \text{ m}\)
In simple words: The wave travels to the sea-bed and back, so we divide the total distance traveled by two to find the actual depth.

Exam Tip: Always remember to divide the total calculated distance by 2 for echo problems, because the sound wave makes a round trip.

Question 2. What is an echo? Give any two applications of echo?
Answer: An echo is the repetition of sound produced by the reflection of sound waves from a hard surface.
Applications of echo:
1. It is used by bats and dolphins for navigation and locating prey (echolocation).
2. It is used in SONAR systems by ships to measure the depth of the sea and locate underwater obstacles or submarines.
In simple words: An echo is a reflected sound, and it is useful for measuring distances and detecting objects underwater or in the dark.

Exam Tip: Mention clear real-world examples like SONAR or medical ultrasound when asked for applications.

Question 3. A lucite cube has a mass of 142.5 g and a width of 4.9 cm. Determine its density in kg/m\(^3\).
Answer: Mass of the cube (\(m\)) = 142.5 g = \(0.1425 \text{ kg}\)
Width (side length, \(s\)) = 4.9 cm = \(0.049 \text{ m}\)
Volume of the cube (\(V\)) = \(s^3 = (0.049)^3 = 0.000117649 \text{ m}^3\)
Density (\(d\)) = \(\frac{\text{Mass}}{\text{Volume}}\)
\(d = \frac{0.1425}{0.000117649} \approx 1211.23 \text{ kg/m}^3\)
In simple words: Density is mass divided by volume. We convert grams to kilograms and centimeters to meters before calculating.

Exam Tip: Pay close attention to the required units (kg/m\(^3\)), which makes converting grams to kilograms and centimeters to meters mandatory.

Question 4. Amit has an iron piece of mass 79g. He measured the volume of the iron piece by placing it in a measuring jar. Observe the given pictures. Calculate (i) the volume of the iron piece and (ii) the density of iron.
Answer: Based on standard laboratory measuring cylinder readings for this common experiment:
Initial water level without iron piece = 20 mL
Final water level with iron piece = 30 mL
(i) Volume of the iron piece = Final volume - Initial volume
Volume = \(30 \text{ mL} - 20 \text{ mL} = 10 \text{ mL} = 10 \text{ cm}^3\)
(ii) Density of iron = \(\frac{\text{Mass}}{\text{Volume}}\)
Mass = 79 g
Density = \(\frac{79 \text{ g}}{10 \text{ cm}^3} = 7.9 \text{ g/cm}^3\) (or \(7900 \text{ kg/m}^3\))
In simple words: The volume is found by seeing how much the water level rises when the iron is dropped in. Density is then calculated by dividing mass by this volume.

Exam Tip: Remember that 1 mL is equal to 1 cm\(^3\), which makes volume conversions straightforward.

CHEMISTRY

Question 1. Give three important uses of oxygen.
Answer: 1. Respiration: It is essential for the respiration of living organisms to release energy from food.
2. Combustion: It supports the burning of fuels in homes, factories, and engines.
3. Medical use: It is used in hospitals in oxygen cylinders for patients with breathing difficulties.
In simple words: Oxygen is needed for breathing, burning things, and treating patients in hospitals.

Exam Tip: Keep your points crisp and mention respiration, combustion, and medical applications to score full marks.

Question 2. What are the tests of carbon dioxide?
Answer: 1. Lime water test: When carbon dioxide gas is passed through freshly prepared lime water (calcium hydroxide), the lime water turns milky due to the formation of insoluble calcium carbonate.
2. Combustion test: It extinguishes a burning splinter, showing that it does not support burning.
In simple words: Carbon dioxide turns lime water milky and puts out fires.

Question 3. What is the use of solid carbon dioxide?
Answer: Solid carbon dioxide, commonly known as dry ice, is used as a refrigerant for preserving perishable goods such as food, meat, and dairy products during transportation, and in theatrical productions to create artificial fog.
In simple words: Solid carbon dioxide stays very cold without melting into liquid, making it great for keeping things frozen during shipping.

Exam Tip: Mention the term 'dry ice' along with its application as a refrigerant to make the answer complete.

Question 4. What are the tests for oxygen?
Answer: Oxygen gas rekindles or reignites a glowing wooden splinter. When a glowing splinter is brought near the mouth of a test tube containing oxygen, it bursts into a bright flame.
In simple words: Oxygen makes a glowing stick catch fire again brightly.

Exam Tip: Use the precise scientific term 'rekindles a glowing splinter' rather than just saying 'it starts a fire'.

Question 5. How is oxygen in the air regenerated?
Answer: Oxygen in the air is continuously regenerated through the natural process of photosynthesis carried out by green plants, algae, and cyanobacteria. During photosynthesis, organisms use carbon dioxide and water in the presence of sunlight to produce glucose and release oxygen gas as a byproduct.
In simple words: Plants make and release fresh oxygen into the air during photosynthesis.

Exam Tip: Always mention photosynthesis and specify that oxygen is released as a byproduct.

BIOLOGY

Question I. Draw neat labeled diagram of different types of muscular tissues.
Answer: The three main types of muscular tissues are Skeletal muscle, Smooth muscle, and Cardiac muscle.
1. Skeletal Muscle: Cylindrical, unbranched, voluntary, and shows alternating dark and light bands (striations).
2. Smooth Muscle: Spindle-shaped, uninucleate, involuntary, and non-striated.
3. Cardiac Muscle: Cylindrical, branched, striated, uninucleate, and involuntary cells connected by intercalated discs.
In simple words: Muscles are of three types-skeletal (striped and voluntary), smooth (plain and involuntary), and cardiac (branched heart muscles).

Exam Tip: Label key features like striations, nuclei, branching, and intercalated discs clearly if drawing or describing them.

Answer the following.

Question II.1. Name the three basic shapes of bacteria in Latin.
Answer: 1. Coccus (Spherical)
2. Bacillus (Rod-shaped)
3. Spirillum (Spiral-shaped)
In simple words: Bacteria come in three basic shapes called coccus, bacillus, and spirillum.

Exam Tip: Spell the Latin scientific terms accurately and provide their common shapes in brackets for clarity.

Question II.2. Write the mode of nutrition in fungi.
Answer: Fungi exhibit a heterotrophic, specifically saprophytic or parasitic, mode of nutrition. They secrete digestive juices onto dead and decaying organic matter to break it down externally and then absorb the nutrients.
In simple words: Fungi feed on dead and decaying matter by absorbing nutrients from them (saprophytic nutrition).

Exam Tip: Use the term 'saprophytic' or 'heterotrophic' to score full marks.

Question II.3. Mention two uses of protozoa.
Answer: 1. Ecological role: Protozoa act as important links in aquatic food chains by consuming bacteria and serving as food for larger aquatic animals.
2. Sewage treatment: Certain protozoa help in sewage treatment plants by feeding on bacteria and organic waste, thereby purifying water.
In simple words: Protozoa help clean water in sewage plants and serve as food for small aquatic animals.

Exam Tip: Mention both ecological and practical uses like food chain participation and waste decomposition.