HEAT BASICS
What is heat?
A form of energy that flows from a hot body to a cold body
Name the three methods of heat transfer.
Conduction, convection, radiation.
What does a thermometer measure?
Temperature.
Why does a woollen sweater keep you warm even though wool is not warm itself?
Wool traps air, and air is a poor conductor of heat.
What happens when heat is added to a body?
The temperature increases, and it may undergo acahnge in state
Why does convection occur only in liquids and gases?
Their molecules can move freely and carry heat with them.
Name the thermometer discussed in Selina for measuring human body temperature. Also mention the range
Clinical thermometer.
Celcius - 35°C to 42°C
Farenhiet - 94°F to 108°F
Why do coastal areas have moderate climates?
Differential heating of land and sea creates regular sea and land breezes.
State the SI unit of heat and the common unit used in the laboratory. And mention the relation between them.
SI unit: joule; Common unit: calorie.
Relation - 1J = 0.24 cal
1cal = 4.2 J
Why are metals good conductors of heat?
Their molecules are packed close toghether, therefore conduction can happen faster.
+ 200 - They contain free electrons which transfer energy rapidly.
Why are gaps left in railway lines ?
To allow expansion of metal rails in summer.
Why is a vacuum used in a thermos flask?
To prevent heat loss by conduction and convection.
Explain why heat is considered energy and not a substance.
Because it is the transfer of energy, not a material that occupies space or has mass.
State the principle behind sea breeze.
Land heats faster than water. The warm air over land rises, causing an LP area. The air above the sea becomes a high-pressure region, and cool air from the sea flows in.
Which expands more on heating: solids, liquids, or gases? Why?
Gases (highest expansion), then liquids, then solids.
If two bodies have the same temperature, does it mean they contain the same amount of heat? Explain.
No. Heat depends on mass and material; temperature only indicates degree of hotness.
Why does a blackened metal surface become hotter in sunlight than a polished metal surface?
Black surfaces absorb more radiant heat. Polished surfaces reflect heat.
Why are cooking utensils made of metal but their handles made of wood or plastic?
Metals conduct heat (good for cooking); wood/plastic are poor conductors (safe to touch).
Explain the melting of water from 0-10 °C.
Mention all processes and why they happen in detail.
Water expands on freezing, from 0-4 °C because of the formation of an open molecular structure of ice.
Upon gaining more energy, it continues to expand and move apart ( more detailed answer should be given)
Why does a glass bottle crack when boiling water is suddenly poured into it, even though the glass may not touch the flame?
The inner surface of the glass expands suddenly due to the hot water, while the outer surface remains relatively cool and does not expand as quickly. This uneven expansion creates stress, causing the glass to crack.