Q1: What is the SI unit of density? (a) g/cm³ (b) kg/m³ (c) kg/cm³ (d) g/m³
Solution:
Ans: (b) Explanation: The SI unit of density is kg/m³ because mass is measured in kilograms and volume in cubic metres in the SI system.
Q2: If the mass of an object increases while its volume remains constant, what happens to its density? (a) Density decreases (b) Density remains the same (c) Density increases (d) Density becomes zero
Solution:
Ans: (c) Explanation: When mass increases and volume stays the same, density increases because density equals mass divided by volume, so more mass means higher density.
Q3: Why does iron have a higher density than wood? (a) Iron has more volume than wood (b) Iron particles are packed more tightly than wood particles (c) Iron has less mass than wood (d) Iron is lighter than wood
Solution:
Ans: (b) Explanation: Iron has a higher density than wood because its particles are packed more tightly, making it heavier for the same volume compared to wood.
Q4: What happens to the density of a substance when it is heated? (a) Density increases (b) Density decreases (c) Density remains constant (d) Density doubles
Solution:
Ans: (b) Explanation: When a substance is heated, it expands and its volume increases. Since density equals mass divided by volume, increased volume causes density to decrease.
Q5: At what temperature is the density of water maximum? (a) 0°C (b) 2°C (c) 4°C (d) 10°C
Solution:
Ans: (c) Explanation: Water is an exception to normal substances. Its density increases from 0°C to 4°C and then decreases above 4°C, making 4°C the point of maximum density.
Fill in the Blanks
Q1: The formula for density is d = M ÷ _____.
Solution:
Ans: V
Q2: The density of water is maximum at _____ degrees Celsius.
Solution:
Ans: 4
Q3: A _____ bottle is used to measure the density of a liquid.
Solution:
Ans: density
Q4: Relative density has no _____ because it is a ratio of two densities.
Solution:
Ans: unit
Q5: Ice floats on water because its density is _____ than water's density.
Solution:
Ans: less
True or False
Q1: The density of a substance changes when its shape or size changes.
Solution:
Ans: False Explanation: The density of a substance does not change with its shape or size; it remains constant as it is a property of the substance.
Q2: Water is denser than oil because water has more mass for the same volume.
Solution:
Ans: True Explanation: Water is denser than oil because for the same volume, water has more mass, indicating that water particles are more tightly packed than oil.
Q3: 1 g/cm³ equals 10³ kg/m³.
Solution:
Ans: True Explanation: The relationship between these units shows that 1 g/cm³ equals 1000 kg/m³, which is written as 10³ kg/m³ in scientific notation.
Q4: An object will sink in a liquid if its density is less than the liquid's density.
Solution:
Ans: False Explanation: An object sinks in a liquid when its density is greater than the liquid's density, not less. Objects float when their density is lower.
Q5: A ship made of iron floats because it is hollow and has a lower overall density than water.
Solution:
Ans: True Explanation: The hollow structure of an iron ship creates empty space inside, reducing its overall density below that of water, allowing it to float.
Match the Following
Solution:
Ans:
1 - C: A measuring cylinder is a graduated vessel made of glass or plastic with markings to show volume for measuring liquids accurately.
2 - E: A Eureka can is a glass or metal container with a spout near its mouth that allows excess liquid to overflow for measurements.
3 - D: A density bottle is a special glass bottle with a stopper that stores a fixed volume of liquid, used to find liquid density.
4 - B: Buoyant force is the upward force exerted on an object in a liquid, equal to the weight of the liquid displaced by the object.
5 - A: The displacement method measures the volume of irregular solids by observing the volume of liquid displaced when the solid is submerged.
Short Answer Questions
Q1: Explain why iron is denser than wood with an example.
Solution:
Ans: Iron has a higher density than wood because its particles are packed more tightly. For example, if we take a piece of iron and a piece of wood of the same volume, the iron will be much heavier. This means iron is more closely packed than wood, making iron denser than wood for equal volumes.
Q2: What is a density bottle and how does it ensure accurate volume measurement?
Solution:
Ans: A density bottle is a special glass bottle used to find the density of a liquid. It has a glass stopper with a narrow hole through it. When the bottle is filled with liquid and the stopper is inserted, any extra liquid rises through the hole and comes out, ensuring the bottle always contains the same fixed volume.
Q3: Describe the displacement method for measuring the volume of an irregular solid.
Solution:
Ans: In the displacement method, a solid when put in a liquid pushes out or displaces the same volume of liquid as its own volume. The initial water level is noted, then the irregular solid is submerged. The difference between the final and initial water levels gives the volume of the irregular solid accurately.
Q4: Why does ice float on water even though it is solid?
Solution:
Ans: Ice floats on water because its density is less than water's density. The density of ice is 0.917 g/cm³, while water's density is 1.0 g/cm³. When ice floats, only one-tenth of it is underwater and nine-tenths is above water. The weight of displaced water equals the ice's total weight.
Q5: How does a submarine control its ability to sink or rise in water?
Solution:
Ans: A submarine has special tanks that can be filled with water or air. When the tanks are filled with water, the submarine becomes heavier and its density increases, causing it to sink. When the tanks are filled with air, the submarine becomes lighter and its density decreases, causing it to rise to the surface.
Long Answer Questions
Q1: Analyze the three cases of floating and sinking based on the relationship between the weight of an object and the buoyant force acting on it.
Solution:
Ans: When an object is placed in a liquid, two forces act on it: weight pulling downward and buoyant force pushing upward. If weight is greater than buoyant force, the object sinks because density exceeds the liquid's density. If weight equals buoyant force, the object floats just inside the surface with zero apparent weight, as densities are equal. If weight is less than buoyant force when fully immersed, the object floats partly above the surface because its density is lower than the liquid's density. In floating, the buoyant force equals weight, making apparent weight zero.
Q2: Compare and evaluate how the density of a substance changes in its three different states: solid, liquid, and gas.
Solution:
Ans: A substance can exist as solid, liquid, or gas, with different densities in each state. In solids, particles are very close together, making them the most dense. In liquids, particles are farther apart, so liquids are less dense than solids. In gases, particles are very far apart, making them the least dense. For example, ice, water, and steam represent these three states, with ice being densest and steam being least dense. This happens because particle spacing determines how much mass occupies a given volume in each state.
Q3: Justify why an iron ship can float on water even though iron has a much higher density than water.
Solution:
Ans: An iron ship floats on water despite iron being denser than water because the ship is hollow with a lot of empty space inside. This hollow structure makes the ship's overall density less than water's density. When placed in water, the ship displaces a large volume of water. According to the law of floatation, the weight of the displaced water equals the ship's total weight. Since the ship's overall density is lower than water due to its hollow design, it experiences sufficient buoyant force to float, even though iron itself would sink.
The document Worksheet with Solutions: Physical Quantities and Measurement is a part of the Class 8 Course Physics Class 8 ICSE.
FAQs on Worksheet with Solutions: Physical Quantities and Measurement
1. What are physical quantities?
Ans. Physical quantities are properties of matter and energy that can be measured and expressed numerically. They include fundamental quantities like length, mass, time, and derived quantities such as velocity and acceleration.
2. What is the importance of measurement in science?
Ans. Measurement is crucial in science as it allows for quantification, comparison, and analysis of physical phenomena. Accurate measurements ensure that experiments can be replicated and that results are reliable.
3. What are the basic units of measurement in the SI system?
Ans. The basic units of measurement in the SI (International System of Units) include the metre (m) for length, kilogram (kg) for mass, second (s) for time, ampere (A) for electric current, kelvin (K) for temperature, mole (mol) for amount of substance, and candela (cd) for luminous intensity.
4. How do you convert units from one system to another?
Ans. To convert units from one system to another, you need to use conversion factors that relate the two units. For example, to convert metres to centimetres, you multiply by 100, since 1 metre equals 100 centimetres.
5. What is the difference between accuracy and precision in measurements?
Ans. Accuracy refers to how close a measured value is to the true value or target, while precision indicates the consistency of repeated measurements. A precise measurement can be inaccurate if it is consistently off from the true value.
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