As per the sign convention that we follow in this class, if an electric motor is considered as a control volume then the shaft work for this control volume is positive. Similarly the shaft work for a pump is negative. Thinking on the same lines Answer the following questions.
A) What would be the sign (positive/negative) of the shaft work for a compressor? Give an explanation for your answer.
B) What would be the sign (positive/negative) of the shaft work of a wind turbine? Give an explanation for your answer.
C) Give an example of a device/control volume/system for which the electrical work is positive. Justify your example with an explanation.
D) Give an example of a device/control volume/system for which the electrical work is negative. Justify your example with an explanation.