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Matter in Our Surroundings
Physics IX : Complete NCERT Exercise Solutions
Explore NCERT Class 9 Science Chapter 1 Matter in Our Surroundings with clear explanations, solved exercise questions, diagrams, and examples. Learn about states of matter, evaporation, condensation, sublimation, and factors affecting change of state for exam preparation.
Question 1.1
Convert the following temperatures to the Celsius scale.
(a) 300 K
(b) 573 K
(a) 300 K
(b) 573 K
Answer & Explanation:
Formula: \( T(°C) = T(K) - 273 \)
(a) \( 300 \, K = 300 - 273 = 27°C \)
(b) \( 573 \, K = 573 - 273 = 300°C \)
(a) \( 300 \, K = 300 - 273 = 27°C \)
(b) \( 573 \, K = 573 - 273 = 300°C \)
Question 1.2
Convert the following temperatures to the Kelvin scale.
(a) 25°C
(b) 373°C
(a) 25°C
(b) 373°C
Answer & Explanation:
Formula: \( T(K) = T(°C) + 273 \)
(a) \( 25°C = 25 + 273 = 298 \, K \)
(b) \( 373°C = 373 + 273 = 646 \, K \)
(a) \( 25°C = 25 + 273 = 298 \, K \)
(b) \( 373°C = 373 + 273 = 646 \, K \)
Question 1.3
Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.
Answer & Explanation:
(a) Sublimation: Naphthalene changes directly from solid to gas without becoming liquid.
(b) Diffusion: Perfume particles mix with air particles and spread due to their kinetic energy.
(b) Diffusion: Perfume particles mix with air particles and spread due to their kinetic energy.
Question 1.4
Arrange the following substances in increasing order of forces of attraction between the particles — water, sugar, oxygen.
Answer & Explanation:
Order: Oxygen < Water < Sugar
• Oxygen (gas): weakest forces
• Water (liquid): intermediate forces
• Sugar (solid): strongest forces
• Oxygen (gas): weakest forces
• Water (liquid): intermediate forces
• Sugar (solid): strongest forces
Question 1.5
What is the physical state of water at—
(a) 25°C
(b) 0°C
(c) 100°C ?
(a) 25°C
(b) 0°C
(c) 100°C ?
Answer & Explanation:
(a) Liquid (room temperature)
(b) Solid (ice) or at melting point (can coexist as solid and liquid)
(c) Gas (water vapour) or at boiling point (can coexist as liquid and gas)
(b) Solid (ice) or at melting point (can coexist as solid and liquid)
(c) Gas (water vapour) or at boiling point (can coexist as liquid and gas)
Question 1.6
Give two reasons to justify—
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.
Answer & Explanation:
(a) Water is liquid at room temperature because:
1. Intermolecular forces are strong enough to hold molecules together but not in fixed positions.
2. Kinetic energy allows molecules to flow.
(b) Iron almirah is solid because:
1. Strong metallic bonds hold atoms in fixed positions.
2. Particles have very low kinetic energy, giving rigidity.
1. Intermolecular forces are strong enough to hold molecules together but not in fixed positions.
2. Kinetic energy allows molecules to flow.
(b) Iron almirah is solid because:
1. Strong metallic bonds hold atoms in fixed positions.
2. Particles have very low kinetic energy, giving rigidity.
Question 1.7
Why is ice at 273 K more effective in cooling than water at the same temperature?
Answer & Explanation:
Ice absorbs additional latent heat from the surroundings to melt into water at 273 K. Water at the same temperature does not absorb latent heat, so ice provides more cooling.
Question 1.8
What produces more severe burns, boiling water or steam?
Answer & Explanation:
Steam produces more severe burns because it releases extra latent heat of vaporisation when it condenses on the skin, in addition to the heat from boiling water.
Question 1.9
Name A, B, C, D, E and F in the following diagram showing change in state.
(Diagram shows interconversion between solid, liquid, gas with heating/cooling and pressure change.)
(Diagram shows interconversion between solid, liquid, gas with heating/cooling and pressure change.)
Answer & Explanation:
A: Melting/Fusion
B: Vaporisation/Boiling
C: Condensation
D: Freezing
E: Sublimation
F: Deposition
B: Vaporisation/Boiling
C: Condensation
D: Freezing
E: Sublimation
F: Deposition
📘 Exam Preparation Tip:
Focus on defining the characteristics of the three states of matter. Practice diagrams for the interconversion of states. Understand the concepts of latent heat, evaporation, and how various factors affect the rate of evaporation with daily life examples.