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Q1. Latent heat of fusion is required to
Latent heat of fusion is the heat energy required to change 1 kg of a solid into liquid at its melting point without any change in temperature. This heat is used to overcome the forces of attraction holding the particles in fixed positions in the solid state. For example, to melt ice at 0°C into water at 0°C, we need to supply latent heat of fusion.
Q2. Arrangement of particles is most ordered in
The arrangement of particles is most ordered in solids. In solids, particles are closely packed in a regular, fixed pattern. This orderly arrangement gives solids their definite shape and volume. In liquids, particles are less ordered, and in gases, they are completely random. Plasma is even more disordered.
Q3. Evaporation is faster when humidity is
Evaporation is faster when humidity is low. Low humidity means the air contains less water vapour, so there is more space for the evaporating water to escape into the air. High humidity slows evaporation because the air is already saturated with moisture. Zero humidity is not common in nature.
Q4. Conversion of water vapour into liquid is called
The conversion of water vapour (gas) into liquid is called condensation. This happens when water vapour loses energy and changes back to liquid form. Examples include water droplets on the outside of a cold glass and the formation of clouds. Condensation is the reverse of evaporation.
Q5. Cotton helps cooling by
Cotton helps cooling by absorbing sweat and allowing evaporation. Cotton is a good absorbent material that soaks up sweat from the body. When the sweat evaporates, it takes latent heat from the skin, causing a cooling effect. This is why cotton clothes are preferred in summer.
Q6. Water droplets on the outer surface of a cold glass are formed due to
Water droplets on the outer surface of a cold glass are formed due to condensation. The water vapour in the air comes in contact with the cold surface of the glass. The vapour loses energy and changes into liquid droplets. This is the same process that forms dew on grass in the morning.
Q7. Sweat cools the body because
Sweat cools the body because it evaporates by absorbing heat. When sweat evaporates from the skin, it takes latent heat of vaporisation from the body, cooling the skin. This is a natural cooling mechanism that helps maintain body temperature. The heat is absorbed from the skin, making us feel cool.
Q8. Which device contains plasma?
A fluorescent tube contains plasma. Inside a fluorescent tube, gas is ionised by electric current, creating plasma. Plasma is a state of matter where gas is ionised and contains free electrons and ions. Electric bulbs have inert gases, heaters have heating elements, and torches use batteries.
Q9. Which scientist was associated with BEC theory?
BEC (Bose-Einstein Condensate) theory was associated with Satyendra Nath Bose, an Indian physicist. He predicted the existence of a new state of matter, and Albert Einstein further developed his work. This is why it is called Bose-Einstein Condensate.
Q10. According to scientists, how many states of matter are now known?
According to scientists, five states of matter are now known: solid, liquid, gas, plasma, and Bose-Einstein Condensate (BEC). The traditional three states (solid, liquid, gas) plus plasma (found in stars and fluorescent tubes) and BEC (formed at extremely low temperatures).
Q11. Evaporation always results in
Evaporation always results in cooling. When a liquid evaporates, it absorbs latent heat of vaporisation from its surroundings. This absorption of heat lowers the temperature of the surroundings, creating a cooling effect. This is why we feel cool when sweat evaporates from our skin.
Q12. Maximum force of attraction between particles is found in
Maximum force of attraction between particles is found in solids. In solids, particles are held together by very strong forces, which keep them in fixed positions. This is why solids have a definite shape and volume and are rigid. The force of attraction is weaker in liquids and even weaker in gases.
Q13. Which statement is correct?
The correct statement is that evaporation causes cooling. When a liquid evaporates, it absorbs heat from the surroundings, causing cooling. Plasma is not neutral gas—it is ionised gas. BEC exists at very low temperatures, not high temperatures. Solids have minimum kinetic energy, not maximum.
Q14. BEC is formed by cooling a gas to
BEC (Bose-Einstein Condensate) is formed by cooling a gas to a very low temperature, close to absolute zero (0 K). At such extremely low temperatures, atoms lose their individual identities and behave as a single quantum entity. This state of matter was predicted by Bose and Einstein.
Q15. Density of gas used to form BEC is
The density of gas used to form BEC is much lower than air. BEC is formed from extremely dilute gases with very low densities. The atoms are spread far apart in a dilute gas, which is then cooled to near absolute zero to form the condensate.
Q16. Rate of evaporation depends on all EXCEPT
The rate of evaporation does NOT depend on the colour of the liquid. It depends on temperature, surface area, humidity, and wind speed. Colour does not affect how quickly a liquid evaporates, though it might affect how much heat the liquid absorbs from sunlight.
Q17. Deposition is the change of
Deposition is the change of state from gas directly to solid. This is the reverse of sublimation. In deposition, a gas changes into a solid without passing through the liquid state. An example is the formation of frost from water vapour on cold surfaces.
Q18. Water droplets on cold glass prove
Water droplets on a cold glass prove condensation. When water vapour in the air comes into contact with the cold surface, it loses energy and changes into liquid droplets. This shows that gases can condense into liquids when cooled.
Q19. Minimum force of attraction between particles is found in
Minimum force of attraction between particles is found in gases. Gas particles are far apart and move freely because the forces of attraction between them are very weak. This is why gases have no definite shape or volume and expand to fill their containers.
Q20. Bose–Einstein Condensate was predicted by
Bose-Einstein Condensate (BEC) was predicted by Satyendra Nath Bose and Albert Einstein. Bose proposed the idea of a new state of matter, and Einstein developed the theory further. The condensate is named after both scientists in recognition of their contributions.
Q21. Sublimation is the change of
Sublimation is the change of state from solid directly to gas without passing through the liquid state. Examples include dry ice (solid CO₂) turning into carbon dioxide gas and camphor disappearing from solid to vapour without melting.
Q22. During evaporation, particles gain energy from
During evaporation, particles gain energy from the surroundings. The liquid absorbs heat from its environment (including the air, the container, and the surface it is on) to provide the energy needed for evaporation. This absorption of energy causes cooling in the surroundings.
Q23. Which conclusion is supported by the text?
The text supports the conclusion that states of matter are inter-convertible. Solids can become liquids (melting), liquids can become gases (evaporation/boiling), and gases can become liquids (condensation) or solids (deposition). These changes can be brought about by changing temperature or pressure.
Q24. States of matter can be changed by changing
States of matter can be changed by changing temperature or pressure. Temperature affects the kinetic energy of particles, and pressure affects the distance between them. By changing these two factors, a substance can be converted from solid to liquid, liquid to gas, or vice versa.
Q25. Cooling during evaporation occurs because
Cooling during evaporation occurs because the surroundings lose energy. When a liquid evaporates, it takes latent heat from the surroundings to provide the energy for vaporisation. This removal of heat from the surroundings lowers their temperature, creating a cooling effect.
Q26. We perspire more in summer to
We perspire more in summer to keep the body cool. Sweating is a cooling mechanism. When sweat evaporates from the skin, it absorbs heat from the body, which helps maintain a stable body temperature. This is the body’s natural way of preventing overheating.
Q27. Sprinkling water on roofs cools them due to
Sprinkling water on roofs cools them due to the large latent heat of vaporisation. When water evaporates from the roof, it absorbs a large amount of heat from the roof surface. This heat is used to change water from liquid to vapour, which cools the roof. The latent heat of vaporisation of water is very high.
Q28. Boiling is called a bulk phenomenon because
Boiling is called a bulk phenomenon because the whole liquid changes into vapour. Unlike evaporation, which occurs only at the surface, boiling happens throughout the liquid. Bubbles of vapour form inside the liquid and rise to the surface, indicating that the change is taking place in the entire bulk of the liquid.
Q29. Latent heat of vaporisation is required to
Latent heat of vaporisation is the heat energy required to change 1 kg of a liquid into gas at its boiling point without any change in temperature. This energy is used to overcome the forces of attraction between particles, allowing them to escape as vapour. It is the heat needed for boiling.
Q30. Nobel Prize for Bose–Einstein condensation was awarded in
The Nobel Prize for the discovery of Bose-Einstein Condensation was awarded in 2001. The prize was given to Eric Cornell, Carl Wieman, and Wolfgang Ketterle for their experimental achievement of creating BEC in dilute gases at ultra-low temperatures.
Q31. Water vapour comes from
Water vapour comes from the water inside. When water is heated, some particles gain enough energy to escape from the liquid surface and become vapour. This vapour then rises and can condense on cooler surfaces. The vapour is coming from the liquid water itself, not from the surroundings.
Q32. Water in an earthen pot becomes cool due to
Water in an earthen pot becomes cool due to evaporation through pores. Earthen pots have tiny pores through which water slowly seeps out and evaporates. This evaporation takes latent heat from the water inside the pot, making the water cool. This is why water in earthen pots stays cool in summer.
Q33. Plasma is formed when gas
Plasma is formed when a gas gets ionised. When gas is heated to very high temperatures, electrons are stripped from atoms, creating ions and free electrons. This ionised gas is called plasma. Plasma is the most common state of matter in the universe, found in stars and the Sun.
Q34. Plasma consists of
Plasma consists of ionised gases. It is a state of matter in which a gas has been heated to such high temperatures that its atoms lose electrons, becoming ions. Plasma contains a mixture of ions, free electrons, and neutral atoms. It is not solid, liquid, or made of neutral atoms only.
Q35. Desert coolers work better on hot dry days because
Desert coolers work better on hot dry days because evaporation is faster. On dry days, the air has low humidity, so water evaporates more easily. The cooler uses this evaporation to cool the air. When humidity is low, the rate of evaporation is higher, making the cooler more effective.
Q36. Matter is made up of
Matter is made up of small particles. All matter—solid, liquid, or gas—is composed of tiny particles that are constantly moving. These particles have spaces between them and exert forces of attraction on each other. Energy, cells, and waves are not the fundamental building blocks of matter.
Q37. Evaporation of sweat takes heat from
Evaporation of sweat takes heat from the body surface. When sweat evaporates, it absorbs latent heat of vaporisation from the skin. This heat is drawn from the body, cooling the skin and helping to maintain body temperature. The heat is taken from the body surface, not just from the air or clothes.
Q38. Plasma in stars is formed due to
Plasma in stars is formed due to very high temperature. Stars, including the Sun, are extremely hot. At these high temperatures, gas atoms are ionised, creating plasma. This is why stars glow and emit light and heat. The high temperature strips electrons from atoms, forming the plasma state.
Q39. Kinetic energy of particles is maximum in
Kinetic energy of particles is maximum in gases. Gas particles move most freely and at the highest speeds. They have the most kinetic energy because they are far apart and have overcome the forces of attraction almost completely. Solids have the least kinetic energy, and liquids are in between.
Q40. Water vapour changes into liquid droplets when it
Water vapour changes into liquid droplets when it loses energy. Condensation occurs when water vapour particles lose kinetic energy and come closer together, changing from gas to liquid. This happens when water vapour comes into contact with a cold surface or when the temperature drops.
Q41. Cotton clothes help evaporation by
Cotton clothes help evaporation by absorbing sweat. Cotton is an absorbent material that soaks up sweat from the body. This increases the surface area for evaporation, allowing more sweat to evaporate and thus providing better cooling. It does not block heat, prevent airflow, or increase humidity.
Q42. The Sun and stars glow due to
The Sun and stars glow due to plasma. Stars are made of plasma, which is ionised gas at extremely high temperatures. The high-energy particles in plasma emit light, causing the stars to glow. This is not due to evaporation, condensation, or combustion (though combustion occurs in the Sun through nuclear fusion).
Q43. Evaporation always leads to
Evaporation always leads to cooling of the surroundings. When a liquid evaporates, it absorbs latent heat from its surroundings, lowering the temperature. This is a fundamental property of evaporation and is why sweating and water evaporation are used for cooling purposes.
Q44. Cotton clothes are preferred in summer because cotton
Cotton clothes are preferred in summer because cotton absorbs sweat easily. Cotton is a natural fibre that can absorb moisture and allow it to evaporate. This helps keep the body cool and comfortable in hot weather. Thick clothes trap heat, and shiny clothes reflect light but are not the main reason.
Q45. Evaporation is called a surface phenomenon because
Evaporation is called a surface phenomenon because only particles at the surface of the liquid escape into the air. Particles below the surface do not have enough kinetic energy to overcome the forces of attraction and escape. This is why evaporation occurs only at the exposed surface of the liquid.
Q46. Which of the following is NOT a state of matter mentioned?
Solution is NOT a state of matter. It is a mixture of two or more substances, not a physical state. The states of matter mentioned are solid, liquid, gas, plasma, and BEC. A solution can be solid, liquid, or gas, but it is not itself a state of matter.
Q47. When acetone is poured on the palm, the palm feels cool because
When acetone is poured on the palm, the palm feels cool because acetone absorbs heat from the palm and evaporates. Acetone has a very low boiling point and evaporates quickly. It takes latent heat of vaporisation from the skin, causing a strong cooling effect. This is why acetone feels cold on the skin.
Q48. Hot tea cools faster in a saucer than in a cup due to
Hot tea cools faster in a saucer than in a cup due to larger surface area. The saucer has a wider surface area, exposing more of the tea to the air. This increases the rate of evaporation and heat loss, causing the tea to cool faster. A smaller surface area (like in a cup) slows down the cooling process.
Q49. Plasma glows because
Plasma glows because of ionisation of gas. When gas is ionised, the electrons and ions recombine, releasing energy in the form of light. This is why fluorescent tubes, neon signs, and stars emit light. The glow is due to the ionisation process, not just because it is hot or has a special colour.