Download Current Electricity History of Electric Current Electric Circuits

Current Electricity
 Objectives/Syllabus
Refs:
 5.1.5:Define
electric current.
resistance.
 5.1.7: Apply the equation for resistance in the form
R = ρL/A
 5.1.8: State Ohm’s Law.
 5.1.9: Compare Ohmic and non-Ohmic behavior.
 5.1.10: Derive and apply expressions for electrical
power dissipation in resistors.
 5.1.11: Solve problems involving potential
difference, current and resistance.
 5.1.6:Define
History of Electric Current
Galvani
vs.
Volta!!!
Electric Circuits

Electric Circuit = closed loop that electric
charge flows through
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Electric Current (I)
Rate
of flow of electric charge
 Technically:
“force per unit length between parallel
current-carrying conductors.”
Measured
André
in Amperes (A)
Ampère (1775-1836)
1
A = 1 C/s
Measured with an ammeter placed in
series
Effect of electric current on you
 0.001
A – Can be felt
 0.005 A – Is painful
 0.01 A – Causes involuntary muscle
contractions (spasms)
 0.015 A – Causes loss of muscle control
 0.070 A – If through the heart, serious
disruption; probably fatal if current lasts for
more than 1 s.
Potential Difference (V)
The
amount of work per unit charge
(or the difference in potential energy
per unit charge)
Measured in Volts (V)
1 V = 1 J/C
Measured with a voltmeter placed in
parallel
Ohm’s law

I = V/R


Not so much a law as a definition of resistance
All conductors have some amount of resistance (R)

R = ρ L/A




ρ (rho) = resistivity of the material
L = length, A = cross-sectional area
1  = the resistance that allows 1 A to flow with 1 V of
potential difference.
Current can be controlled from a given voltage by
altering the resistance (light dimmers)
When do light bulbs
usually burn out and
why?
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Power (P)
The
rate at which work is done or
energy is “used” (transferred).
Measured in Watts (W)
1
P
W = 1 J/s
Power (Cont)
P
= IV
P = I2R
P = V2/R
= IV
(C/s)
J/C = J/s = Watts
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