Transfer
Hwa Chong Institution Sec 3 (SMTP) Name: ________________________________________ Class: __________ Date: ___________
Sec 3 Physics (SMTP) Topic 10: Transfer of thermal energy
THERMAL EQUILIBRIUM & THE ZEROTH LAW OF THERMODYNAMICS Thermal Equilibrium If you want to know the temperature of a cup of hot coffee, you stick a thermometer in the coffee. As the two interact, the thermometer becomes hotter and the coffee cools off a little. After the thermometer settles down to a steady value, you read the temperature. The system has reached an equilibrium condition; further interaction between the thermometer and the coffee cause no more changes. This is a state of thermal equilibrium. If the systems are separated by an insulator, such as wood, plastic or fiber glass, they influence each other more slowly. An ideal insulator is a material that permits no interactions at all between the two systems. It prevents the systems from attaining thermal equilibrium if the systems are not in thermal equilibrium at the start. That’s why ice is packed in insulating materials so that the insulation delays the process of achieving thermal equilibrium with the surrounding. Zeroth law of thermodynamics If system A is in thermal equilibrium with system C, and system B is in thermal equilibrium with System C, then System A and System B must be in thermal equilibrium. Important implication:
THERMAL ENERGY & HEAT Thermal energy is also frequently described as internal energy of a system. The internal energy of a system is the sum of kinetic energy and potential energy possessed by the molecules of the system. Heat is the amount of thermal energy transferred from a region of higher temperature to a region of lower temperature. Important note: Heat and work are energy in transit. A body does not contain work; a force is needed to transfer energy between two interacting mechanical system. Likewise, a body does not contain heat; heat is the transfer of energy between two systems due to
Sec 3 Physics (SMTP) Topic 10: Transfer of thermal energy
THERMAL EQUILIBRIUM & THE ZEROTH LAW OF THERMODYNAMICS Thermal Equilibrium If you want to know the temperature of a cup of hot coffee, you stick a thermometer in the coffee. As the two interact, the thermometer becomes hotter and the coffee cools off a little. After the thermometer settles down to a steady value, you read the temperature. The system has reached an equilibrium condition; further interaction between the thermometer and the coffee cause no more changes. This is a state of thermal equilibrium. If the systems are separated by an insulator, such as wood, plastic or fiber glass, they influence each other more slowly. An ideal insulator is a material that permits no interactions at all between the two systems. It prevents the systems from attaining thermal equilibrium if the systems are not in thermal equilibrium at the start. That’s why ice is packed in insulating materials so that the insulation delays the process of achieving thermal equilibrium with the surrounding. Zeroth law of thermodynamics If system A is in thermal equilibrium with system C, and system B is in thermal equilibrium with System C, then System A and System B must be in thermal equilibrium. Important implication:
THERMAL ENERGY & HEAT Thermal energy is also frequently described as internal energy of a system. The internal energy of a system is the sum of kinetic energy and potential energy possessed by the molecules of the system. Heat is the amount of thermal energy transferred from a region of higher temperature to a region of lower temperature. Important note: Heat and work are energy in transit. A body does not contain work; a force is needed to transfer energy between two interacting mechanical system. Likewise, a body does not contain heat; heat is the transfer of energy between two systems due to