Grade 7 Q&A: Chapter 6: Measurement of Physical Quantities

Concept Questions

Q1: What is a physical quantity? Give two examples.

Answer: A physical quantity is a property of a phenomenon, body, or substance that can be quantified by measurement. Examples include length, mass, time, temperature, force, and velocity.

Q2: Differentiate between scalar and vector quantities.

Answer:

• Scalar Quantities: Have only magnitude (size or amount) but no direction. Examples: Length, mass, time, speed.
• Vector Quantities: Have both magnitude and direction. Examples: Displacement, velocity, force, acceleration.

Q3: What are fundamental units? Name three fundamental SI units.

Answer: Fundamental units (or base units) are units that are independent of each other and cannot be expressed in terms of other units. They form the basis of a system of measurement. Three fundamental SI units are: metre (m) for length, kilogram (kg) for mass, and second (s) for time.

Q4: What are derived units? Give two examples.

Answer: Derived units are units that are obtained by combining two or more fundamental units. Examples include: 1. Square metre ($m^2$) for area (derived from length $\times$ length). 2. Metre per second (m/s) for speed (derived from length / time).

Q5: What is the SI unit of length, mass, and time?

Answer:

• SI unit of length: metre (m)
• SI unit of mass: kilogram (kg)
• SI unit of time: second (s)

Q6: How is the area of a regular shape like a rectangle calculated?

Answer: The area of a regular shape like a rectangle is calculated by multiplying its length by its breadth (Area = Length $\times$ Breadth).

Q7: How can the area of an irregular shape be measured?

Answer: The area of an irregular shape can be measured using graph paper. The shape is drawn on graph paper, and the number of full squares and more-than-half squares within the shape are counted. Half squares are often counted as 0.5.

Q8: What is the SI unit of volume? Name two common instruments used to measure the volume of liquids.

Answer: The SI unit of volume is the cubic metre ($m^3$). Two common instruments used to measure the volume of liquids are a measuring cylinder and a beaker.

Q9: How is the volume of an irregular solid measured?

Answer: The volume of an irregular solid is measured using the water displacement method (based on Archimedes' principle). The solid is submerged in a known volume of water in a measuring cylinder; the increase in the water level indicates the volume of the solid.

Q10: What is the relationship between litre and cubic centimetre?

Answer: 1 litre (L) is equal to 1000 cubic centimetres ($cm^3$). Also, 1 millilitre (mL) is equal to 1 cubic centimetre ($cm^3$).

Q11: Why is accurate measurement important in scientific experiments?

Answer: Accurate measurement is crucial in scientific experiments to ensure that the results obtained are reliable, precise, and can be reproduced consistently by other researchers. This allows for valid conclusions and advancements in scientific understanding.

Q12: Name the common instruments used to measure length and mass.

Answer:

• Common instruments for measuring length: Measuring tape, ruler, metre scale.
• Common instruments for measuring mass: Beam balance, electronic balance.

Q13: What is the difference between speed and velocity?

Answer: Speed is a scalar quantity, indicating only how fast an object is moving (magnitude). Velocity is a vector quantity, indicating both how fast an object is moving and in what direction (magnitude and direction).

Q14: What is the definition of density? Write its derived unit.

Answer: Density is defined as mass per unit volume. Its derived SI unit is kilogram per cubic metre ($kg/m^3$).

Q15: Give an example of how measurement is important in everyday life.

Answer: Measurement is important in everyday life for tasks like cooking (measuring ingredients), driving (checking speed, distance), timing events (using a clock/stopwatch), and purchasing goods (weighing vegetables, measuring cloth).

Application-Based Questions

Q16: A student measures the length of a table using a hand span. Why might this method lead to inaccurate results?

Answer: Using a hand span to measure the length of a table would lead to inaccurate results because a hand span is not a standard unit of measurement. Its length varies from person to person, meaning different individuals would get different measurements for the same table, making the results unreliable and non-comparable.

Q17: You are asked to measure the amount of water in a beaker. Which instrument would you use for a more precise measurement, and why?

Answer: For a more precise measurement of the amount of water in a beaker, you would use a **measuring cylinder**. While a beaker can hold liquids, a measuring cylinder has precise markings and a narrower diameter, allowing for more accurate readings of liquid volume compared to a beaker.

Q18: A car travels 100 km in 2 hours. What physical quantity can you calculate from this information, and what type of quantity is it?

Answer: From this information, you can calculate the **speed** of the car (Speed = Distance / Time = 100 km / 2 hours = 50 km/h). Speed is a **scalar quantity** because it only tells you how fast the car is moving, not its direction.

Q19: Explain how you would find the volume of an irregularly shaped stone using common laboratory equipment.

Answer: To find the volume of an irregularly shaped stone, I would use the **water displacement method**. I would take a measuring cylinder, fill it with a known volume of water, and note the initial water level. Then, I would carefully lower the stone into the water until it is fully submerged. The new, higher water level would be noted. The difference between the final and initial water levels would give the volume of the stone.

Q20: Why is it important for engineers and construction workers to make accurate measurements?

Answer: It is critically important for engineers and construction workers to make accurate measurements because precision directly impacts the safety, stability, and functionality of structures. Inaccurate measurements can lead to structural failures, material waste, increased costs, and pose significant risks to human life. For example, incorrect measurements for a bridge could lead to its collapse.

Q21: A chef needs to measure 500 grams of flour for a recipe. Which instrument should they use to ensure accuracy?

Answer: The chef should use an **electronic balance** (or a kitchen scale) to ensure accurate measurement of 500 grams of flour. While a beam balance could also work, an electronic balance provides a digital and often more precise reading for cooking purposes.

Q22: If you are given the task of measuring the area of a leaf, which method would be most suitable? Explain why.

Answer: The most suitable method for measuring the area of a leaf (which is an irregular shape) would be using **graph paper**. You would trace the leaf onto graph paper and then count the number of full squares and estimate the number of half or more-than-half squares covered by the leaf. This method provides a reasonable approximation of the irregular area.

Q23: Why is it essential to have a standard system of units like SI units for scientific communication?

Answer: It is essential to have a standard system of units like SI units for scientific communication to ensure clarity, consistency, and avoid confusion. A universal system allows scientists worldwide to understand and replicate each other's experiments and data without ambiguity, facilitating global collaboration and the advancement of knowledge.

Q24: A runner completes a 100-meter race in 12 seconds. What two physical quantities are being measured here, and what are their respective SI units?

Answer: The two physical quantities being measured are: 1. **Length/Distance:** 100 meters. Its SI unit is the **metre (m)**. 2. **Time:** 12 seconds. Its SI unit is the **second (s)**.

Q25: If you are designing a new type of battery, why would understanding the concept of 'electric current' (a fundamental SI quantity) be important?

Answer: Understanding 'electric current' (measured in Amperes, A) is crucial because it represents the flow of electric charge. In designing a battery, you need to control and predict how much current it can deliver, for how long, and at what voltage. This directly impacts the battery's power output, capacity, and overall efficiency, which are critical for its performance and safety.

Textbook Exercise Solutions

A. Fill in the blanks:

1. The SI unit of length is the metre.
2. Mass is measured using a beam balance or electronic balance.
3. The SI unit of time is the second.
4. Area is a derived quantity.
5. Volume of an irregular solid can be found using the water displacement method.

B. Match the following:

Column A

1. Length
2. Mass
3. Time
4. Area
5. Volume

Column B

1. Kilogram
2. Second
3. Square metre
4. Cubic metre
5. Metre

Answers:

1. Length - Metre
2. Mass - Kilogram
3. Time - Second
4. Area - Square metre
5. Volume - Cubic metre

C. Answer the following questions:

Q1: What are physical quantities? Give examples of scalar and vector quantities.

Answer: Physical quantities are properties of a phenomenon, body, or substance that can be quantified by measurement.

• Scalar Quantities: Have only magnitude (size or amount). Examples: Length, mass, time, temperature, speed, area, volume, density.
• Vector Quantities: Have both magnitude and direction. Examples: Displacement, velocity, acceleration, force, weight.

Q2: Explain fundamental and derived units with examples.

Answer:

• Fundamental Units: These are independent units that cannot be expressed in terms of other units. They form the basic set of units from which all other units are derived. Examples: metre (m) for length, kilogram (kg) for mass, second (s) for time.
• Derived Units: These units are obtained by combining two or more fundamental units through multiplication or division. Examples: square metre ($m^2$) for area (m $\times$ m), metre per second (m/s) for speed (m/s), kilogram per cubic metre ($kg/m^3$) for density (kg/$m^3$).

Q3: How is the area of an irregular object measured?

Answer: The area of an irregular object is typically measured using graph paper. The irregular object (or its outline) is placed on graph paper. The number of full squares completely enclosed by the object's boundary is counted. Then, the squares that are more than half-filled are also counted as one. Squares that are less than half-filled are ignored. The sum of these counts gives an approximate area of the irregular object in square units of the graph paper.

Q4: Describe the method to find the volume of an irregular solid.

Answer: The volume of an irregular solid can be found using the water displacement method (also known as Archimedes' principle).

1. Take a measuring cylinder and fill it with a known volume of water. Note this initial volume ($V_1$).
2. Carefully tie the irregular solid with a thread and gently lower it into the measuring cylinder until it is completely submerged in the water.
3. Note the new, higher volume of water in the cylinder ($V_2$).
4. The volume of the irregular solid is the difference between the final and initial volumes: Volume of solid = $V_2 - V_1$.

Q5: Why is accurate measurement important in daily life?

Answer: Accurate measurement is very important in daily life for several reasons:

• Cooking and Baking: Precise measurements of ingredients ensure the desired taste and texture of food.
• Health and Medicine: Accurate dosages of medicines are vital for effective treatment and patient safety.
• Construction and Engineering: Exact measurements ensure the safety, stability, and proper functioning of buildings, bridges, and other structures.
• Trade and Commerce: Fair transactions depend on accurate measurements of goods (e.g., weight of vegetables, length of cloth).
• Time Management: Accurate timekeeping helps in scheduling, transportation, and daily routines.

References

1. Maharashtra State Board 7th Standard Science Syllabus (Based on current curriculum for measurement of physical quantities)
2. Screenshot_2025_0527_234813.jpg (Provided content and exercise questions)