Mastery

Heat Transfer in Nature — Mastery

30 questions 30 min Full-chapter mastery

Q1. Pema's grandmother prepares thukpa in a metal pan because, from Class 6 Science, the family knows that metals such as steel and aluminium
- A. Are poor conductors of heat and so keep the food warm
- B. Reflect most of the heat away from the food
- C. Do not allow the flame to touch the pan from outside
- D. Are good conductors of heat and so pass the flame's heat to the food quickly
Q2. Pema and Palden sit around a fireplace in Gangtok and feel its warmth even though they are not touching the flame and there is no strong wind blowing the hot air to them. This everyday experience is meant to prepare the reader for which mode of heat transfer?
- A. Conduction along the floor
- B. Convection through the cold winter air only
- C. Radiation directly from the fire to the children
- D. Evaporation of moisture from their clothes
Q3. Palden notes that Kerala is generally warmer than Sikkim. From the chapter's opening discussion, the main reason for this is that
- A. Kerala lies at a higher altitude than Sikkim
- B. Kerala has more forests than Sikkim
- C. Kerala lies closer to the equator and is along the coast, so it receives more direct sunlight
- D. Kerala has more rivers than Sikkim
Q4. Which of the following sentences best describes how heat moves from one end of a hot metal rod to its colder end?
- A. The hot particles physically run along the rod from one end to the other
- B. The colder particles are pushed out of the rod to make space for the heat
- C. Heat jumps across the rod without any role of the particles
- D. Each heated particle passes its heat to the next neighbouring particle, and so the heat travels along the rod
Q5. While setting up Activity 7.1, the chapter advises that the candle should be placed at the free end of the metal strip — that is, the end away from the stand or clamp that holds the strip. The main reason is that
- A. The clamp would catch fire if the candle were placed near it
- B. The wax pins would not stick to the strip near the clamp
- C. The pins must be on the same side as the clamp for the picture to look neat
- D. Heat must flow from the heated free end along the strip towards the cold end, so the pins fall in a clear order
Q6. Suppose Activity 7.1 is repeated with a wooden strip or a glass strip in place of the metal strip, keeping everything else the same. The most likely observation is that
- A. All pins will fall at the same time, faster than on metal
- B. Pins will fall in the reverse order — pin IV first, then III, II, I
- C. Pins will fall in the same order as on metal, but slightly more slowly
- D. The pins will not fall (or will take a very long time), because wood and glass are poor conductors of heat
Q7. Before lighting the candle in Activity 7.1, the chapter asks the students to first predict the order in which the four pins will fall and write it down in Table 7.1. The pedagogical purpose of this 'predict-before-doing' step is to
- A. Make students notice their own prior idea and then compare it with the actual observation
- B. Help the teacher decide whether the candle is safe to light
- C. Ensure that the activity finishes within the period
- D. Give marks to students whose prediction matches
Q8. Which one of the following sets contains only poor conductors of heat?
- A. Iron, copper, aluminium
- B. Wood, glass, clay, porcelain
- C. Steel, brass, silver
- D. Aluminium foil, copper wire, iron nail
Q9. Many of the insulation examples in the chapter — wool, two thin blankets, hollow bricks, the second tumbler around the lassi tumbler — work for the same underlying reason. That reason is
- A. Cotton and metal are both good radiators of heat
- B. Water vapour gets trapped in these arrangements and conducts heat away
- C. Sunlight gets reflected by these arrangements before it can reach the inside
- D. Air gets trapped in pores or gaps, and air is a poor conductor of heat
Q10. In Mori village of Uttarkashi (Uttarakhand), traditional houses have walls made of two layers of wood with a filling of dung-and-mud in between. Why does such a wall keep the rooms warm in winter and cool in summer?
- A. Dung-and-mud is a very good conductor of heat and constantly heats the room
- B. The wood layers and the dung-mud filling are all poor conductors of heat, and air trapped in their pores further reduces heat flow through the wall
- C. Wood layers reflect the entire winter sunlight straight back into the room
- D. Dung-and-mud is the only material from which heat can never pass
Q11. A family in a hot region of Rajasthan wants to build a new house that stays cool in summer without using an air conditioner. Using the chapter's idea of insulation, which design choice will help the most?
- A. Build outer walls of hollow bricks so that air is trapped within the walls and heat flow from outside to inside is reduced
- B. Build the outer walls of solid iron sheets so that they conduct heat into the rooms quickly
- C. Make the roof of a single thin metal sheet with no insulation
- D. Use as much glass as possible on the south-facing wall to absorb maximum sunlight
Q12. Convection takes place mainly in
- A. Solids only
- B. Solids and liquids only
- C. Solids and gases only
- D. Liquids and gases (i.e., fluids)
Q13. A partially inflated balloon, when kept in the bright Sun for some time, is observed to become more inflated. The best reason from the chapter is that
- A. Sunlight passes through the balloon and adds extra air from outside
- B. The rubber of the balloon shrinks and pushes the air outward
- C. The air inside the balloon gets heated, expands and pushes the balloon walls outward
- D. Water from the air condenses inside the balloon and fills it up
Q14. From Activity 7.4 and the discussion that follows, which of the following statements about soil and water is correct?
- A. Soil and water heat up at the same rate but cool at different rates
- B. Soil heats up faster than water but cools down slower than water
- C. Soil heats up slower than water but cools down faster than water
- D. Soil heats up faster than water and also cools down faster than water
Q15. Sea breeze and land breeze are best classified as natural examples of
- A. Convection currents in air on a large scale
- B. Conduction of heat through the soil
- C. Radiation from the Sun to the Earth
- D. Insulation by the atmosphere
Q16. Mrs. Sharma is teaching Activity 7.1 (pins on a metal strip) to her Class 7 students. Which sequence of teaching steps best follows the chapter's predict-observe-explain pedagogy?
- A. Light the candle, write the result on the board, then ask students to copy it into their notebooks
- B. Show a video of the activity first, then read out the answer from the textbook, then test on the next day
- C. Demonstrate the activity once silently, then ask students to memorise the order I → II → III → IV
- D. Ask students to predict and record the order in Table 7.1 first, then perform the activity together, and finally discuss why the prediction matched or did not match
Q17. A Class 7 student says, "When I hold an ice cube, cold from the ice flows into my hand and makes my hand cold." Which is the most effective way for the teacher to address this misconception, in keeping with the chapter?
- A. Explain that heat actually flows from the hand (hotter) to the ice (colder) by conduction, and demonstrate this idea with the wax-and-pins Activity 7.1
- B. Tell the student that the textbook does not discuss ice cubes, so the question is outside the syllabus
- C. Ask the student to memorise that 'cold cannot flow' and write it five times in the notebook
- D. Say that both ideas — heat moving and cold moving — are equally correct in physics
Q18. A school is fitting smoke detectors in classrooms in Delhi. From the chapter's reasoning about why smoke rises, the device will work earliest if it is fitted
- A. Inside a cupboard on the floor
- B. On the lower part of a side wall, near the floor
- C. On the teacher's desk, at table-top height
- D. On the ceiling of the classroom, away from any direct opening
Q19. In the upper Himalayas, a traditional iron room-heater called bukhari is used in winter. Consider the following statements about a bukhari being used to cook on top and warm the room around it: I. Heat passes from the burning wood through the iron body of the stove by conduction. II. Air around the bukhari is warmed by convection currents in the room. III. The warmth we feel sitting some distance from the bukhari is by radiation. Which of the statements is/are correct?
- A. I and II only
- B. II and III only
- C. I and III only
- D. All three
Q20. A thin sheet of paper is wrapped tightly around a thick metal rod and the wrapped rod is held briefly in a flame. The paper does not burn easily. The best reason from the chapter is that
- A. Paper cannot burn when it is wrapped around any solid
- B. The flame is not hot enough to burn the paper
- C. The metal rod conducts heat away from the paper quickly, so the paper does not reach its burning temperature easily
- D. The metal rod reflects the flame's heat back into the flame
Q21. A pan of water is placed on a gas flame (Fig. 7.8). The water at the bottom of the pan first gets heated, expands, becomes lighter and rises up; cooler water from the top moves down to take its place. The water in the pan as a whole therefore gets heated mainly by
- A. Conduction
- B. Convection
- C. Radiation
- D. Insulation
Q22. Assertion (A): A hot metal utensil, taken off the flame and left untouched on a wooden table in still air, cools down to room temperature after some time. Reason (R): The hot utensil radiates heat to its surroundings. Choose the correct option.
- A. Both A and R are true, and R is the correct explanation of A.
- B. Both A and R are true, but R is NOT the correct explanation of A.
- C. A is true, R is false.
- D. A is false, R is true.
Q23. In Shimla, people often prefer to wear dark-coloured clothes during winter days when they sit out in the sun. The best scientific reason from the chapter is that dark-coloured clothes
- A. Reflect most of the sunlight back into the surroundings
- B. Have a thicker weave than light-coloured clothes
- C. Trap the body's perspiration and recycle the heat
- D. Absorb most of the heat falling on them, so the wearer feels warmer
Q24. In the water cycle, plants also contribute water vapour to the atmosphere by losing water from their leaves. This process is called
- A. Evaporation
- B. Condensation
- C. Transpiration
- D. Precipitation
Q25. Wet clothes hung on a clothesline dry faster on a sunny day than on a cloudy day. The best reason from the chapter is that
- A. Heat from the Sun makes evaporation of water from the clothes faster
- B. Sunny days have stronger winds than cloudy days
- C. Clothes themselves produce more heat when sunlight falls on them
- D. Water in the clothes turns directly into snow on a sunny day
Q26. Consider the following statements about Varahamihira, mentioned in the 'Know a Scientist' box of this chapter: I. He was a sixth-century astronomer and mathematician from Ujjaini (modern-day Ujjain). II. In his work Brihatsamhita, he gave methods for predicting seasonal rainfall. III. His predictions were based on factors such as cloud formation, wind patterns and positions of stars and the moon. Which of the statements is/are correct?
- A. I and II only
- B. II and III only
- C. I and III only
- D. All three
Q27. A village in Bundelkhand depends mostly on water drawn from wells and bore wells. The water that they draw out of the ground is, according to this chapter
- A. Water that condenses inside the well overnight
- B. Water flowing in an underground river
- C. Water that has just fallen as fresh rain into the well
- D. Water stored in the pore spaces of an aquifer below the ground
Q28. Consider the following measures to help replenish groundwater in a town: I. Building rainwater harvesting structures on rooftops to direct rainwater into pits. II. Replacing more roads and pavements with continuous concrete cover. III. Digging recharge pits in open ground so that rainwater can seep into the soil. Which of the measures will help replenish groundwater?
- A. I and II only
- B. II and III only
- C. I and III only
- D. All three
Q29. In Ladakh, farmers face water scarcity in early spring because streams have dried up and snow has not yet melted. The ice stupa addresses this problem mainly because
- A. It prevents rainfall from being lost as runoff during the spring
- B. It stores winter water as ice and slowly melts in spring, providing water for farming and other needs through the summer
- C. It works only because Ladakh receives heavy monsoon rainfall
- D. It produces fresh water by condensing water vapour from the air
Q30. Riya argues that coastal towns like Kochi experience milder summers and milder winters than inland towns like Nagpur because a large water body nearby prevents extreme temperatures. Which is the best reason from the chapter to judge Riya's argument as correct?
- A. Water heats up slowly in summer and cools down slowly in winter, so a nearby sea limits the rise and fall of temperatures in coastal areas
- B. Salt water present in the sea is itself an insulator that blocks heat from the Sun
- C. Sea breeze blows only in summer and land breeze only in winter, so each works half the year
- D. Coastal areas receive less sunlight overall than inland areas

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