Heat

Similarities:

1. Both have a long, narrow, uniform glass tube.
2. Both have a bulb at one end containing mercury.
3. Both have a Celsius scale.

Differences:

• Conductors: Aluminium, Iron, Copper (Metals).
• Insulators: Plastic, Wood, Air, Water.

(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 is dipped in a cup of hot milk. Heat is transferred to its other end by the process of conduction.

(f) Clothes of dark colours absorb more heat better than clothes of light colours.

Wearing more layers of clothing keeps us warmer because air gets trapped in between the layers. Air is a poor conductor of heat (insulator). This trapped air prevents the flow of heat from our body to the cold surroundings.

(Ref: Diagram of a pan on a stove)

• Conduction: Transfer of heat from the burner to the pan (and handle).
• Convection: Transfer of heat within the water (water becoming hot).
• Radiation: Transfer of heat from the hot pan/stove to the surroundings.

White colour reflects most of the heat that falls on it. Therefore, painting outer walls white helps the house to not absorb much heat and keeps it cooler inside.

(d) between 30°C and 50°C.

(b) not flow from iron ball to water or from water to iron ball (because both are at same temperature).

Mercury is used because:

1. It expands uniformly with heat.
2. It does not stick to the walls of the glass tube.
3. It is shiny and easy to see.

The normal temperature of human body is 37°C or 98.6°F.

• Heat: Form of energy that causes sensation of hotness or coldness. Flows from hot object to cold object.
• Temperature: Reliable measure of hotness of an object. Measured in Degree Celsius (°C).

• Clinical Thermometer: Measures body temperature. Range 35°C to 42°C. Has a kink (constriction) to prevent mercury falling back. Normal body temp = 37°C.
• Laboratory Thermometer: Measures temp of objects. Range -10°C to 110°C. No kink. Read while bulb is in contact with substance.

• Conduction: Transfer of heat in solids from hot end to cold end. (e.g. Spoon in hot tea). Metals are good conductors.
• Convection: Transfer of heat in liquids and gases by movement of particles. Hot air rises, cold air takes its place. (e.g. Boiling water, Sea Breeze).
• Radiation: Transfer of heat without any medium. (e.g. Sun's heat reaching earth).

• Sea Breeze (Day): Land heats faster. Hot air rises. Cool air from sea flows towards land.
• Land Breeze (Night): Land cools faster. Water is warmer. Cool air from land flows towards sea.

• Clinical thermometer range: **35°C to 42°C**.
• In **Construction**, bricks are hollow to trap air (insulator) and keep houses cool in summer.
• Dark clothes absorb more heat than light clothes.
• Heat from sun cannot reach us by conduction or convection as there is no air in space. It comes by **Radiation**.