Heat — Practice Quiz

That heat causes convection currents in water where hot water rises and cold water sinks

Step 1: When water near the bottom is heated, it becomes less dense (lighter) and rises to the top. Step 2: The cooler, denser water from the sides and top sinks to take its place near the heat source. Step 3: The potassium permanganate crystals dissolve and colour the water, making these invisible currents VISIBLE. Step 4: The circular movement of coloured water (up in the middle, down on the sides) clearly shows convection currents. Step 5: This is how heat transfer by CONVECTION works in liquids — through actual movement of the fluid particles, unlike conduction where only vibration occurs.

Land heats up faster than sea, hot air over land rises, and cooler air from the sea rushes in to take its place

Step 1: During the day, solar radiation heats the land faster than the sea because land has lower specific heat capacity. Step 2: The air above the land gets heated by conduction and convection, becomes lighter, and rises upward. Step 3: This creates a low pressure region over the land. Step 4: The cooler, denser air from over the sea moves horizontally toward the land to fill this low pressure zone — this is the sea breeze. Step 5: At night, the process reverses — land cools faster, sea stays warmer, so air blows from land to sea (land breeze). Option D describes the night pattern, not the da

Radiation — because it does not need any medium and can travel through vacuum, unlike conduction and convection which require a material medium

Step 1: Conduction requires physical contact between particles of a solid medium — there is no solid connecting the Sun and Earth, so conduction is impossible. Step 2: Convection requires a fluid (liquid or gas) to carry heat through bulk movement — space between Sun and Earth is mostly vacuum, so convection cannot occur. Step 3: Radiation transfers heat in the form of electromagnetic waves (infrared radiation) that do NOT need any medium. Step 4: These radiation waves travel through the vacuum of space at the speed of light and reach Earth. Step 5: When this radiation hits objects on Earth, p

The black can will have lower temperature because dark surfaces radiate (lose) heat faster than light surfaces

Step 1: Dark (black) surfaces are good ABSORBERS of heat — this is a well-known property. Step 2: The same property makes them good EMITTERS (radiators) of heat as well. Step 3: So the black can will radiate its heat to the surroundings faster than the white can. Step 4: The white can is a poor emitter, so it loses heat more slowly and stays warmer. Step 5: After 20 minutes, the black can will be at a lower temperature. This principle is why dark clothes feel hotter in the sun (absorb more) and also cool down faster at night. Option C is wrong because the rate of heat loss differs between the