# Circuit Elements ```PHYS-1500 PHYSICAL MODELING
FALL 2006
Circuit Elements
A resistor is familiar to most students of high school physics. Its symbol is:
The potential difference (or voltage) across a resistor is proportional to the current passing
through it. V = – iR, where i is the current, and R is the resistance. The minus sign means that
the potential decreases in the direction that the current flows.
A capacitor is symbolized by:
The potential difference (or voltage) across a capacitor is proportional to the charge on it. V = –
q/C, where q is the charge, and C is the capacitance. The minus sign means that the potential
decreases in passing from the positively charged plate to the negatively charged plate.
An inductor is symbolized by:
The potential difference (or voltage) across an inductor is proportional to the rate of change of
di
current through it. V   L , where i is the current, and L is the inductance. The minus sign
dt
means that the potential decreases in the direction of increasing current.
A source of emf is often symbolized by:
The longer parallel line indicates the side that is at higher potential (the positive side).
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