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Current- the movement of charge.
Symbol is I, unit is the Ampere (A)
I = q/t
1 A = 1 C/s
Conventional current- from the positive
terminal to the negative terminal.
Drift velocity- the speed in which
individual electrons move within the
conductor, opposite the electric field.
The drift velocity is relatively small.
• Resistance- the opposition to the flow of
charge by a material or device.
• Symbol is R, unit is ohms (W).
• Ohms law R = V/I or V = IR
• Resistance depends on the following
factors:
Length – short wires have less resistance
Area- thick wires have less resistance
Material- different materials have different
conductivity of charge
Temperature- heat slows the flow of charge.
Power
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Power is energy used per time.
The unit of power is a Watt = Joule/sec
P= PE/t, or P=IV
You can use Ohm’s Law to substitute in
the equation, creating two other equations,
P=I2R, or P=V2/R.
Series Circuits
• In a series circuit, there is only one
pathway for current, so the current is the
same everywhere.
• Resistors add up in series. R+R+R=Rtotal
• Kirchhoff’s rule- Voltage drops must equal
the starting voltage, or V-IR-IR=0.
• Ohm’s Law holds for all parts of the circuit.
Advantages/Disadvantages
• Advantages of a Series Circuit- easy to
hook up, needs fewer wires, the current is
the same everywhere.
• Disadvantages- uses more current, if one
device goes out, or a wire comes loose,
the whole circuit stops working.
Parallel Circuits
• In a parallel circuit, there are multiple
pathways for current.
• Resistance in parallel is less than the
smallest parallel branch.
• 1/R + 1/R = 1/Rtotal
• Voltage is the same across both branches.
• Current divides up in parallel, path of least
resistance gets more current. V/R=I
Advantages/Disadvantages
• Advantages of Parallel- the resistance is
lower, more current can be used
effectively, more devices can be hooked
into the same voltage source. If one
device goes out, the others continue
working.
• Disadvantages of Parallel- more difficult to
connect, uses more wires.