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Home Minds On Electric Circuits Mission EC3 Voltage, Power and Energy Help Help 1

Mission EC3 Voltage, Power and Energy

The Question

The metric unit of work is the ____ and the metric unit of power is the ____.

Formula Fix

Mathematically, work (W) is calculated from knowledge of the force (F) that acts upon an object, the displacement (d) that the force causes, and the angle (Theta) between the force and displacement vectors. The formula is
 
W = F • d • cosine(Theta).


Mathematically, power is a rate quantity - a time-based quantity. It is the rate at which a force does work upon a charge. Power (P) is calculated from knowledge of the work done (W) and the time (t) required to do this work. The formula is

P = W / t.

Think About It

It is often the case that the units of a quantity can be determined from the formula for the quantity. In the case of work, the units would be a unit of force multiplied by a unit of displacement. This would be a Newton • meter, abbreviated N•m. The unit Joule, abbreviated J, is defined to be equivalent to a N•m. Thus, Joule is the standard unit of work in the metric system.
 
In the case of power, the units would be a unit of work divided by a unit of time. This would be a Joule/second, abbreviated J/s. The unit Joule/second is defined to be equivalent to a Watt. Thus, Watt is the standard unit of power in the metric system.

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