Questions of Effects of Colour and Nature of Surface on Radiation - Questions at the end of the chapter - Chapter 7 Class 7 - Heat Transfer in Nature (Curiosity)

Last updated at May 3, 2026 by

Q3 (Medium): Explain why the bottom of cooking vessels is often made black.

Answer:
We have studied that dark surfaces are better absorbers of heat radiation . This is why cooking vessels have black bottoms:

  • Black surfaces absorb more heat from flame
  • Better heat absorption means faster cooking
  • Efficient heat transfer saves fuel and time
Why Black Bottom Vessels Step 1 - Flame radiates heat Fire produces heat radiation Step 2 - Black absorbs more Dark surface absorbs maximum heat Step 3 - Heat transfers up Absorbed heat cooks food faster Efficient cooking!

Q4 (Medium): Why are light-coloured clothes preferred in summer and dark-coloured clothes in winter?

Answer:
We have studied that light surfaces reflect heat while dark surfaces absorb heat . This explains clothing choices:

  • Light clothes in summer reflect heat away
  • Dark clothes in winter absorb heat better
  • Body temperature stays comfortable in both seasons
Summer vs Winter Clothing Season Summer (Light Clothes) Winter (Dark Clothes) Heat interaction Reflect heat radiation Absorb heat radiation Body effect Keeps body cool Keeps body warm Comfort level Prevents overheating Prevents heat loss

Q7 (Medium): Describe an activity to show that dark surfaces absorb more heat than light surfaces.

Answer:
We have studied that surface colour affects heat absorption . Here is the activity:

  • Take two identical metal cans
  • Paint one black, keep one shiny
  • Fill both with equal cold water
  • Place under heat lamp for 30 minutes
  • Black can shows higher temperature rise
Dark vs Light Surface Activity Step 1 - Prepare cans One black painted, one shiny Step 2 - Add cold water Equal amounts in both cans Step 3 - Heat equally Same distance from heat lamp Step 4 - Measure temperature Black can gets hotter Dark absorbs more heat!

Q9 (Medium): A student wore a black shirt on a hot sunny day and felt very hot. Explain using the concept of radiation.

Answer:
We have studied that dark surfaces are better absorbers of heat radiation . This explains the student's experience:

  • Sun radiates heat energy toward Earth
  • Black shirt absorbs maximum solar radiation
  • Absorbed heat makes student feel very hot
Black Shirt Heat Absorption Step 1 - Sun radiates Solar radiation reaches student Step 2 - Black absorbs Dark shirt absorbs heat radiation Step 3 - Heat transfers Absorbed heat warms student's body Student feels very hot!
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