Power and Energy

Question 2

Power is equivelant to how many joules per second?

Answer 2

Power (W) = J/s

1 Watt = 1 Joule per second

P =Vi

(voltage*current)

Question 3

Passive sign convention.

Explain.

Answer 3

Voltage is a difference of charge between two places in space. Not an absolute quality. You could think of it in terms of depth and height.

Something has an elevation or height only with respect to something else such as sea level. Likewise depth, something is only deep compared to some level, again such as sea level.

Power flowing out of a circuit into an electrical component is positive +

Power flowing into a circuit out of an electrical component is negative -

Example.

An electric charge Q at point A gets moves from a higher potential to a lower potential (i.e from points A to B). Since the charge is leaving at a lower potential the charge has lost potential energy. This is called a resistor. If the charge moves from B to A it gains potential energy. This is called a source.