Download Electric Charge

Electric Current
Electric Current
• The rate at which electrical
charges flow through a wire or
conductor is called electric
current.
Electrical current = charge passing through a given area / time
I = Δq/Δt
SI Unit = C/s = Amperes (A)
Electric Current
Sample Problem
The current in a light bulb is 0.835 A.
How long does it take for a total
charge of 1.67 C to pass a point in
the wire?
I = Δq/Δt
Δq = 1.67 C
I = 0.835 A
Δt = Δq/I = 1.67 C / 0.835 A =
2.00 s
Electric Current
• Charges flow from high voltage to
low voltage.
– A voltage difference is the push
that causes charges to move.
– Voltage difference is measured in
volts (V).
– For charges to flow, the wire must
always be connected in a closed
path, or circuit.
Electric Current
Electric field travels
at the speed of light,
but the charges do
not!!!
Drift Velocity: The
net velocity of a
charge moving in an
e- field.
Types of Current
• 2 Types:
1. Direct current (DC)
- Electrical charges move only in one
direction.
- Batteries always generates a direct
current (why?……fixed voltage
difference).
Direct Current
Types of Currents (cont.)
2. Alternating current (AC)
- Electrical charges are constantly
changing directions.
- Commonly used in homes and
businesses throughout the world.
Why?
More efficient for long-distance
electrical charge transmission.
Alternating Current
Sources of electrical current
• A dry cell battery produces a
voltage difference
– zinc container
– carbon suspension rod
– causing current to flow between
them.
• Example: AA battery
Dry Cell Battery
Sources of electrical current (Cont.)
• A wet cell battery contains two
connected plates made of
different metals in a conducting
solution.
–Example: Car battery
Sources of electrical current (Cont.)
Generators
- Convert mechanical energy to
electrical energy.
- Can produce both direct and
alternating current.
Sources of electrical current (Cont.)
• Wall sockets have a
voltage difference
across the two
holes of an
electrical outlet.
– generator at a power
plant provides this
voltage difference.