Transcript Electric current

Objectives:
S1-3-09 Define electric current as
charge per unit time and solve related
problems.
Include:
Electric Current
• Electrical devices need a steady flow of electricity.
The flow continues until the energy source is used
up, or disconnected.
• Electric current is a measure of the rate at which
electric charges move past a given point in a
conductor per second. Simply put, it is the speed
that the electrons are moving at.
• Ammeter is a tool used to measure the electric
current in a circuit.
Calculating Electric Current
Symbol
What does it mean?
Units
I
Current
Amperes (A)
Q
Amount of Charge
Coulombs (C)
t
Time
Seconds (S)
Current – I
Units are Ampere (A)
Ammeters only record the huge number of
electrons passing through the conductor – current.
1 coulomb equals (6.25 x 1018) electrons.
1 coulomb per 1 second = 1 A
Calculating Electric Current
• An easy way to calculate current is by using
the following equation:
• The triangle can be put into three equations:
Q
I = ----t
Q=
I
X
t
t=
Q
----I
Converting Time to Seconds
• Remember time needs to be in seconds.
Convert the following into seconds:
– Convert 20 minutes into seconds
– Think about it? How many seconds are in a
minute?
– 20 minutes x
60 s
1 min.
= 1,200 seconds in 20 minutes
Converting Time to Seconds
• Remember time needs to be in seconds.
Convert the following into seconds:
– Convert 3 hours into seconds
– Think about it? How many seconds are in an hour?
– 3 hours x 3600 s
1 hour
= 10 800 seconds in 3 hours
G. U. E. S. S. Method for Solving Problems
• Use the G. U. E. S. S. method to solve problems.
G: Given
U: Unknown
E: Equation
S: Substitution
S: Solution
Example 1
• How much time does it take for 80 C to pass
through a light that draws on 0.4 amperes?
Example 2
• How many electric charges pass through an
appliance that draws 40 Amps over 30
minutes?
Calculating Electric Current
• The symbol for current is I and the units are
amperes(A).
• The symbol for quantity of electric charge is
Q and the units are coulombs (C).
• Time is measured in seconds.
• Current is measured using an ammeter.
Analogy
CONSIDER THE FOLLOWING…
From Static to Current Electricity
What is static electricity?
• Electric charge builds up on
an object
• The charge is static
• Electrons move when
discharged to another
object by contact
What is current electricity?
• Electrons flow
• Electrons move through a
conductor such as a wire
• Moves from the negative to
the positive
• Requires energy to move
the electrons
Chemical reactions in the cell constantly produce
free electrons – accumulate on negative electrode.
Electrons move from the (-) electrode (repelled)
through the conducting loop to the (+) electrode
(attracted).
Ammeter:
Tool to measure the
electric current in a
circuit.
Electric current and hazards
0.8A
0.2 A
– charge needed to light a 100W bulb
– severe burns, heart stops, lungs stop.
0.02 A
0.002 A
(“let go” threshold)
– breathing affected, muscles contract
– muscles tingle.
Dry cell:
Electrolyte is a thick paste (acid or salt).
Makes for easy handling – batteries.
Rod: + electrode
(cathode)
Casing: - electrode
(anode)
electrolyte
paste
Voltage
Units are volts (V) – measured by a voltmeter
Energy per 1 coulomb of e- = 1 V
550 V
120 V
9V
1.6 V
– potential energy of a Power station.
– potential energy of home wall outlet.
– smoke alarm battery
– AA battery
5.5 Volt battery
Pot. energy in an e- - 5.5 Volts
0 Volts
Voltage - 5.5 Volts
(el. pot. difference)
+ electrode
electrolyte
paste
- electrode
5.5 Volts
• Metals or electrolytes allow electrons to flow.
• Electric current is the movement of electrons in a
circuit.
• Cells have positive and negative electrodes.
• Electrons build up on the negative electrode.
• Current is the amount of e- moving – coulomb
• Current is measured in Amperes.
• Voltage is the difference between the potential
energy of electrons at two point in a circuit.
• Voltage is measured in Volts.
• Circuits can been drawn in symbols – schematic.