20 Important Words (Meanings in Hindi)

• Heat — ऊष्मा: गर्मी का रूप जो ऊष्मा ऊर्जा बताता है
• Temperature — तापमान: किसी वस्तु की गरमी/ठंडक का माप
• Thermometer — तापमापी: तापमान मापने का यंत्र
• Clinical Thermometer — चिकित्सीय तापमापी: शरीर का तापमान मापने हेतु
• Laboratory Thermometer — प्रयोगशाला तापमापी: सामान्य वस्तुओं/तरल के ताप हेतु
• Celsius Scale — सेल्सियस मापनी: °C में तापमान
• Fahrenheit Scale — फॉरेनहाइट मापनी: °F में तापमान
• Conduction — चालन: ठोस में कणों द्वारा ऊष्मा का संचरण
• Convection — संवहन: द्रव/वायु में गरम भाग ऊपर, ठंडा नीचे
• Radiation — विकिरण: बिना माध्यम के ऊष्मा का संचरण
• Conductor — चालक: जो ऊष्मा आसानी से गुजरने दे
• Insulator — रोधक: जो ऊष्मा को रोकता है
• Sea Breeze — समुद्री पवन: दिन में समुद्र से भूमि की ओर हवा
• Land Breeze — स्थलीय पवन: रात में भूमि से समुद्र की ओर हवा
• Mercury — पारा: द्रव धातु, थर्मामीटर में प्रयुक्त
• Kink — किंक/नॉच: क्लीनिकल थर्मामीटर में पारा लौटने से रोकने वाली रोधी गांठ
• Expansion — प्रसार: गर्म होने पर फैलना
• Black Surface — काली सतह: अधिक ऊष्मा अवशोषित करती है
• White/Light Surface — सफ़ेद/हल्की सतह: ऊष्मा का अधिक परावर्तन
• Wool — ऊन: ऊष्मा रोधक, रेशों में हवा फँसी रहती है

Important Notes (Quick Revision)

• Sense of touch can be misleading; the reliable measure of hotness is temperature measured by a thermometer.
• Clinical thermometer: range \(35^{\circ}\mathrm{C}\) to \(42^{\circ}\mathrm{C}\), has a kink to prevent mercury from falling back when taken out.
• Laboratory thermometer: range about \(-10^{\circ}\mathrm{C}\) to \(110^{\circ}\mathrm{C}\); read while its bulb is still in the substance; keep upright.
• Heat always flows from hotter to colder body.
• Conduction (solids): metals are good conductors; wood/plastic are insulators.
• Convection (liquids & gases): hot fluid rises, cold fluid sinks → currents (e.g., sea & land breeze).
• Radiation: no medium needed (Sun’s heat; room heater; hot utensil cooling).
• Dark colours absorb more heat; light colours reflect more → wear light in summer, dark in winter.
• Woollen clothes keep warm because wool + trapped air are poor conductors of heat.
• Normal human body temperature ≈ \(37^{\circ}\mathrm{C}\) (may vary slightly).

20 One-Word Answer Type (Answers in 1–2 lines)

1. Device to measure temperature?
   Thermometer (clinical/laboratory as per use).
2. Unit of temperature used in NCERT?
   Degree Celsius \((^{\circ}\mathrm{C})\).
3. Normal body temperature?
   About \(37^{\circ}\mathrm{C}\).
4. Range of clinical thermometer?
   \(\,35^{\circ}\mathrm{C}\) to \(42^{\circ}\mathrm{C}\,\).
5. Range of lab thermometer (typical)?
   \(\,-10^{\circ}\mathrm{C}\) to \(110^{\circ}\mathrm{C}\,\) (approx.).
6. Heat transfer in solids mainly?
   Conduction.
7. Heat transfer in liquids/gases mainly?
   Convection.
8. Heat transfer without medium?
   Radiation.
9. Good conductor example.
   Copper/Aluminium/Iron.
10. Insulator example.
    Wood/Plastic.
11. Sea breeze blows when?
    Daytime.
12. Land breeze blows when?
    Night.
13. Colour that absorbs more heat?
    Black/dark colours.
14. Why wool keeps warm?
    Poor conductor + trapped air.
15. Part of clinical thermometer stopping mercury fall?
    Kink (constriction).
16. Why not use clinical thermometer for hot milk?
    Limited range; may break; meant only for body temperature.
17. Air above a flame feels ______.
    Hotter (due to convection).
18. We wear light clothes in ______.
    Summer.
19. We wear dark clothes in ______.
    Winter.
20. Digital thermometers avoid using ______.
    Mercury.

20 Very Short Answer Type (1–2 lines)

1. Why is touch unreliable for hot/cold judgement?
   Because our skin adapts; prior exposure can mislead (hot–cold water activity).
2. State the direction of natural heat flow.
   From hotter object to colder object.
3. How to read a thermometer correctly?
   Keep eye along mercury level; note value between marked divisions.
4. Why clinical thermometer has a kink?
   To prevent mercury from falling back while reading.
5. Why must lab thermometer be read while in liquid?
   Mercury level falls immediately when taken out.
6. Why cooking pan handles are plastic/wood?
   They are insulators—prevent burns.
7. What are convection currents?
   Circulation formed as hot fluid rises and cold fluid descends.
8. Name the three modes of heat transfer.
   Conduction, Convection, Radiation.
9. Why do we get warm in sunlight?
   Heat reaches us by radiation from the Sun.
10. Why light clothes in summer?
    They reflect most radiation → feel cooler.
11. Why dark clothes in winter?
    They absorb more heat → feel warmer.
12. Why two thin blankets can be better than one thick?
    Air trapped between blankets adds insulation.
13. Why keep clinical thermometer away from flame?
    Excess heat can break it and mercury is toxic.
14. What creates sea breeze?
    Land heats faster; warm air rises; cool sea air rushes in.
15. What creates land breeze?
    At night land cools faster; cool land air moves to sea.
16. Why umbrella in summer?
    To block radiation and reduce absorbed heat.
17. Name a poor conductor liquid used for cooking heat transfer.
    Water (convection distributes heat).
18. Which part of a flame region feels hottest by hand test?
    Above the flame (rising hot air).
19. State one precaution with lab thermometer.
    Keep it upright; bulb not touching container walls/bottom.
20. What is the maximum-minimum thermometer used for?
    Recording daily max/min air temperatures (weather).

20 Short Answer Type (about 2–3 lines)

1. Differentiate clinical vs laboratory thermometer.
   Clinical: \(35^{\circ}\mathrm{C}\)–\(42^{\circ}\mathrm{C}\), kink, for body only. Lab: \(\approx -10^{\circ}\mathrm{C}\)–\(110^{\circ}\mathrm{C}\), no kink, for general use; read while immersed.
2. Explain conduction with a metal strip & wax activity.
   Heated end warms adjacent particles; wax pieces fall in order from near flame to far end → heat flows by conduction.
3. How does convection heat a pot of water?
   Water near flame gets hot and rises; cooler water descends; continuous currents distribute heat.
4. Why is radiation important for Earth’s heat?
   Space is nearly vacuum; Sun’s heat reaches Earth via radiation (no medium required).
5. Why do cooking utensils often have copper bottoms?
   Copper is a better conductor than steel → faster, uniform heating; efficient cooking.
6. Why do we use light-coloured clothes in summer?
   They reflect most incident radiation → less heat absorbed → cooler body.
7. State two precautions while using a clinical thermometer.
   Disinfect before/after use; ensure mercury below \(35^{\circ}\mathrm{C}\); don’t hold by bulb; handle carefully.
8. Why can’t lab thermometer measure body temperature conveniently?
   It has no kink; reading must be taken while immersed; mercury falls once removed.
9. How do woollens keep us warm?
   Wool + trapped air are poor conductors; reduce heat loss from body to surroundings.
10. Explain sea breeze with cause.
    Day: land heats quickly → warm air rises → cool sea air flows toward land (sea breeze).
11. Explain land breeze with cause.
    Night: land cools quickly → cool air moves toward relatively warmer sea (land breeze).
12. What is the correct way to read small divisions on a thermometer?
    Find value between two large marks, divide by number of small divisions, then count small ticks to mercury level.
13. Why is a black surface hotter in sun than a white surface?
    Black absorbs more radiation; white reflects more, absorbing less heat.
14. State one reason to avoid mercury thermometers.
    Mercury is toxic and difficult to dispose safely if the thermometer breaks.
15. Why does a metal spoon in hot tea become hot at the other end?
    Heat conducted along the spoon’s metal lattice from hot end to cold end.
16. Why are hollow bricks useful for thermal comfort?
    Trapped air layers reduce heat transfer—cooler in summer, warmer in winter.
17. Which hand feels hotter near a candle: above or side? Why?
    Above—hot air rises by convection; sides feel comparatively cooler.
18. Why should the bulb of a lab thermometer not touch the beaker bottom?
    Bottom may be hotter/colder than liquid; ensures accurate reading of the liquid itself.
19. Why is it advised to paint outer walls white in hot places?
    White reflects sunlight, reducing heat absorption by the building.
20. State the three common ways to reduce heat loss from body in winter.
    Wear layers (trapped air), use woollens (insulation), prefer dark colours (more absorption outdoors).

NCERT Exercise – Perfect Answers (Chapter 3: Heat)

1. 1. Similarities & differences: laboratory vs clinical thermometer.
   Similarities: Both have glass tubes with bulbs containing mercury (or sensor), marked Celsius scale; measure temperature. Differences: Clinical range \(35^{\circ}\mathrm{C}\)–\(42^{\circ}\mathrm{C}\), has kink, used for human body; Lab range about \(-10^{\circ}\mathrm{C}\)–\(110^{\circ}\mathrm{C}\), no kink, used for substances; lab reading must be taken while bulb remains immersed and upright.
2. 2. Two conductors & two insulators of heat.
   Conductors: Copper, Aluminium. Insulators: Wood, Plastic.
3. 3. Fill in the blanks.
   (a) The hotness of an object is determined by its temperature.
   (b) Temperature of boiling water cannot be measured by a clinical thermometer.
   (c) Temperature is measured in degree Celsius.
   (d) No medium is required for transfer of heat by the process of radiation.
   (e) A cold steel spoon in hot milk gets heat to its other end by conduction.
   (f) Clothes of dark colours absorb more heat than clothes of light colours.
4. 4. Match the following.
   (i) Land breeze blows during → (d) night
   (ii) Sea breeze blows during → (c) day
   (iii) Dark coloured clothes are preferred during → (b) winter
   (iv) Light coloured clothes are preferred during → (a) summer
5. 5. Why more layers keep us warmer than one thick piece?
   Layers trap multiple air films between them; air is a good insulator, so total heat loss reduces more than with a single thick layer.
6. 6. Mark modes of heat transfer in Fig. 3.13 (concept).
   From flame to pot: radiation; through metal pot: conduction; water circulating: convection; heat radiating to surroundings: radiation.
7. 7. Why paint outer walls white in hot climate?
   White reflects most solar radiation, reducing heat absorption and keeping interiors cooler.
8. 8. Mix 1 L at \(30^{\circ}\mathrm{C}\) with 1 L at \(50^{\circ}\mathrm{C}\): temperature?
   (d) Between \(30^{\circ}\mathrm{C}\) and \(50^{\circ}\mathrm{C}\) (approximately the average here, neglecting losses).
9. 9. Iron ball at \(40^{\circ}\mathrm{C}\) in water at \(40^{\circ}\mathrm{C}\): heat will?
   (b) Not flow either way (same temperature).
10. 10. Wooden spoon dipped in ice-cream: other end?
    (d) Does not become cold (wood is a poor conductor).
11. 11. Steel pans with copper bottoms because?
    (c) Copper is a better conductor of heat than stainless steel (efficient heating).

Important Equations & Reminders

Normal body temperature: \(37^{\circ}\mathrm{C}\).

Heat flow direction: \(Q\) flows from higher \(T\) to lower \(T\).

No medium needed for radiation: Sun \(\rightarrow\) Earth via radiation.

Convection currents: Hot fluid \(\uparrow\), Cold fluid \(\downarrow\) → circulation.

Labeled Diagrams (Simple SVG Sketches)