What is the SI unit of the heat transfer rate qdot?

What is the SI unit of the heat transfer rate qdot?

• A. Joule
• B. Newton
• C. Pascal
• D. Watt

Answer: (D)

Heat transfer rate qdot is the amount of heat transferred per unit time. Since it is a rate, its unit comes from energy per time: heat is measured in joules, and dividing by time gives joules per second. In SI, joules per second is defined as the watt, symbol W. So qdot has units of watts (1 W = 1 J/s). A joule is energy, not a rate, so it doesn’t describe how fast heat moves. A newton is a unit of force, and a pascal is a unit of pressure, neither of which describe heat flow rate. The watt directly represents the rate of energy transfer, which matches qdot.

Heat transfer rate qdot is the amount of heat transferred per unit time. Since it is a rate, its unit comes from energy per time: heat is measured in joules, and dividing by time gives joules per second. In SI, joules per second is defined as the watt, symbol W. So qdot has units of watts (1 W = 1 J/s).

A joule is energy, not a rate, so it doesn’t describe how fast heat moves. A newton is a unit of force, and a pascal is a unit of pressure, neither of which describe heat flow rate. The watt directly represents the rate of energy transfer, which matches qdot.