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Electric Current
Lesson 9
Electric Current
Electric current is what makes electricity
so dangerous.
 In solids only negative electric charges
move.
 Electric current is the measure of the rate
at which electric charges move past a
given point in a circuit.

Electric Current
The metric SI unit used to measure
electric current is the ampere. The
symbol for ampere is A.
 Slightly less than one ampere (1 A) flows
through a 100W light bulb in a 120 V
circuit.
 Current is measured by using an ammeter
connected to the circuit in series.

Current
Current is the movement of electrical
charge. The flow of electrons through the
electronic circuit.
 Current would be the flow of water
moving through the tube (wire). If the size
of pipe is increased more water will flow
through it.

Human Response to Electric
Shock

The electric potentials created in the
body for muscle movement are around
0.08V. The stronger the current is, the
more the muscles contract. If the current
is large enough, the part of the body in
which the current is flowing will contract
and remain contracted until the current
ceases.
Human Response to Electric
Shock

Most people do not feel anything below
0.001 A. at 0.002 A tingling is felt. When
the current reaches 0.016 A muscles will
contract or convulse. If this current were
to pass through the chest it could
paralyze the breathing muscles. If a
current of 0.05 A passes through the
chest for a few seconds, the heart will
stop pumping. Electric current above 0.2
amps causes severe burns.
Electrical Resistance
Electrical Resistance

All types of conductors impede the flow
of electrons to some extent. This is called
electrical resistance. Some kinds of
electrical devices are designed for this
purpose and are called resistors.
Electrical Resistance
The symbol for electrical resistance is R,
and the SI unit is the ohm (Ω).
 When electrons flow through a
conductor, the electrical resistance causes
a loss of electrical energy or Voltage.

Ohms Law
The potential difference between two
points on a conductor is proportional
(directly related) to the electric current
flowing through the conductor.
 In other words, the voltage drops when it
passes through a conductor.

Ohms Law
V=IxR
 Potential Difference = Electric Current x
Electrical Resistance.


This formula allows us to calculate how
much resistance is in the circuit.
Example
What is the voltage of a car battery with
800 Amps of current and 0.015 Ohms?
 I = 800 A
 R = 0.015 Ω
V=?

V=IxR
 V = (800 A) x (0.015 Ω)
 = 12 V


Therefore, the car battery is 12 V.

Measuring Current in a Circuit Lab