Download Electric Current Introduction

Electric Current Introduction
What would happen if you put a small
positive charge between two plates?
+
+
+
+ + + +
+ + + + + + + +
+ + + + + + + + +
+

E
–
–
–
–
–
–
–
–
–
–

E
–
–
–
–
–
high potential
(high energy per charge)
–
–
–
–
–
–
–
–
–
low potential
What if you just connected the two
plates with a metal wire?
+
+
+

E
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
current
q
I
t
–
–
–
–
–
–
–
–
–
–
+
+
+
+
+
high potential
(high energy per charge)
+ charge will flow from high
potential to low potential until
plates are neutralized.
–
–
+
–
–
–
–
–
–
–
–
–
–
–
–
low potential
Electric Current
q
I
t
• The rate of flow of electric charge.
• Measured in C/s or Amps (A).
• Conventional current is defined to be the
direction of flow of positive charge.
How could you make the flow of
current constant?
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+

E
+
+
+
high potential
(high energy per charge)
DO WORK!
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
low potential
Vocabulary
• Voltage (V) – aka electric potential difference
[Volts – V]
• Current (I) – rate of flow of charge [Amps – A]
– Direct current (dc) – same direction all times
– Alternating current (ac) – changes direction
• Resistance (R) – how much the flow of charge
restricted [Ohms – Ω]
L
R
A
ρ = resistivity [Ω∙m]
L = length [m]
A = area [m2]
Copper has a very
low resistance
which is why it is
often used for wiring.
What is the relationship between
voltage, current, and resistance?
• Use what you know about finding
mathematical relationships to find
“Ohm’s Law” with a rheostat.
V  IR
Power
U e qV q
P

 V  IV
t
t
t
P  IV
2
V
P  IV  I R 
R
2