Chapter 6 Temperature and Heat

Notes

Temperature and Heat

• Temperature is a measure of how hot or cold something is, often measured using a thermometer.

• Heat is the energy transferred from a hot object to a cold object due to temperature difference.

Heat Flow

• Heat flows from an area of higher temperature to an area of lower temperature.

• The flow continues until the two objects reach thermal equilibrium (same temperature).

Thermometers and Temperature Scales

• Thermometers are based on the expansion and contraction of materials like mercury or alcohol with changes in temperature.

• There are three primary temperature scales:

  1. Celsius (°C): Based on water's freezing and boiling points (0°C and 100°C).

  2. Fahrenheit (°F): Freezing point is 32°F, boiling point is 212°F.

  3. Kelvin (K): Scientific scale with absolute zero as 0K.

Heat Transfer Mechanisms

1. Conduction:

   • Happens when two objects are in direct contact.

   • Metals are good conductors because their free electrons transfer heat energy.

   • Example: Heating one end of a metal rod makes the other end hot.

2. Convection:

   • Occurs in liquids and gases.

   • Warm air or fluid rises, and cool air or fluid sinks, creating a convection current.

   • Example: Boiling water – hot water rises while cool water sinks.

3. Radiation:

   • Involves electromagnetic waves (light, infrared) that can transfer heat without the need for matter.

   • Heat is absorbed when radiation strikes an object.

   • Example: The heat you feel from the Sun is transferred through radiation.

Applications of Heat Transfer

1. Solar Panels: Absorb sunlight (radiation) and convert it into electricity or heat.

2. Microwave Ovens: Use microwave radiation to heat food.

3. Thermal Imaging: Detects heat differences using infrared radiation.

4. Laser Technology: Uses focused light to apply heat to precise areas for cutting or medical purposes.

Mercury Thermometers

• Mercury expands or contracts in a glass tube to measure temperature.

• Kink in the thermometer prevents the mercury from moving backward, ensuring accurate reading.

Why Mercury is Harmful

• Minamata Disease: Caused by mercury contamination, particularly from fish in water polluted by chemical waste.

Heat Transfer Examples

• Conduction: Cooking with a metal spoon in a hot pan.

• Convection: Air conditioning or heating systems using convection currents.

• Radiation: Heat from the Sun reaching Earth, microwaves heating food.

Important Concepts

1. Celsius Scale: 0°C (freezing point) and 100°C (boiling point) for water.

2. Fahrenheit Scale: Freezing point 32°F, boiling point 212°F.

3. Kelvin Scale: Absolute zero is 0K.