Question

Definitions of efficiency vary depending on how energy is being converted. Compare the definitions of efficiency for the human body and heat engines. How does the definition of efficiency in each relate to the type of energy being converted into doing work?

Short answer

The efficiency of a heat engine is the ratio of mechanical work to thermal energy and the efficiency of the human body is the ratio of mechanical work to chemical energy.

Step-by-step solution

Explain which type of energy conversion takes place in the human body and heat engine.

In a heat engine, heat transfer occurs from a hot reservoir to a cold reservoir. This heat transfer is responsible for the work done in the heat engine. Here, thermal energy is converted into mechanical energy.

In the human body, the food that enters the body produces chemical energy, and this is responsible for the energy of the human body. So, here, chemical energy is converted into mechanical energy.

Describe how efficiency and energy conversion are related.

Efficiency can be generally defined as the ratio of work output to energy input. So, this definition of efficiency varies with the different forms of energy conversion. In a heat engine, the work output is equal to the mechanical work and the input is equal to the thermal energy, whereas in the human body, work output is equal to the mechanical work and the input is equal to the chemical energy.

So, the definition of efficiency varies with the type of energy conversion that takes place in the system.