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Current and
Ohm’s Law
Current is the rate
at which charges go by
I = DQ / Dt
Measured in amperes (amps)
Small current
Larger current
Lower current
e
e
e
e
e
e
e
e
e
Higher current
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Problems
1. What is the current through a light if
a charge of 2.50 C passes through it in
2.00 s?
2. How many electrons passed through?
Current is defined as the movement
of positive charges.
p+ = e -
Electron drift velocity is slow
But transmission of info is fast
Electric current can be:
Direct or Alternating
Ohm’s Law
DV = IR
DV potential difference
I current
R resistance
Potential Difference (voltage)
It is related to the energy that would be required to
move a unit of electrical charge from one point to the
other against the electrostatic field that is present.
Unit: joules per coulomb = volt
Resistance
How much a conductor resists
the flow of electricity
Unit: ohm (W)
Problems
1. A circuit hooked up to a 12 V battery
shows a current of 2.5 amps. What is the
resistance in the circuit?
2. How many electrons go by a spot in
that circuit in 5 seconds?
Electric Power:
The rate at which charge carriers
change electrical PE to other forms
P = IDV
P = I2R
P = (DV)2/R
Problem
A refrigerator has a resistance of
78W and a current of 1.5 A. What
is its power and voltage?