Transcript 1. Junction rule – conservation of charge.

Drift speed
When you connect a circuit, current flows IN EVERY PART of the
circuit instantaneously (near the speed of light).
• ALL free electrons in the circuit start moving the
moment the circuit is connected / the moment the
electric field is applied.
• Batteries create potential difference, they do NOT
supply electrons; the electrons come from the
wire.
Drift speed
When you connect a circuit, current flows IN EVERY PART of the
circuit instantaneously (near the speed of light).
• ALL free electrons in the circuit start moving the
moment the circuit is connected / the moment the
electric field is applied.
• Batteries create potential difference, they do NOT
supply electrons; the electrons come from the
wire.
Electrons move very fast (106 ms-1), but are not instantaneous.
Drift speed
When you connect a circuit, current flows IN EVERY PART of the
circuit instantaneously (near the speed of light).
• ALL free electrons in the circuit start moving the
moment the circuit is connected / the moment the
electric field is applied.
• Batteries create potential difference, they do NOT
supply electrons; the electrons come from the
wire.
Electrons move very fast (106 ms-1), but are not instantaneous.
Because electrons bounce around due to collisions with atoms
in the wire, the average speed of electrons opposite
the flow of current – known as drift speed –
is VERY slow (0.01 cm/s)
Drift speed
When you connect a circuit, current flows IN EVERY PART of the
circuit instantaneously (near the speed of light).
• ALL free electrons in the circuit start moving the
moment the circuit is connected / the moment the
electric field is applied.
• Batteries create potential difference, they do NOT
supplyThis
electrons;
theitelectrons
from the 3
means
can takecome
an electron
wire.
hours to travel through 1 m of wire!
Electrons move
veryeven
fast (10
ms-1), but
are not instantaneous.
it’s not
a 6snail’s
pace!!!!!
Because electrons bounce around due to collisions with atoms
in the wire, the average speed of electrons opposite
the flow of current – known as drift speed –
is VERY slow (0.01 cm/s)
Drift speed
Turn & Talk with your table partner
…The scholar with the bigger shoe size
Define drift speed
… The scholar with the smaller shoe size
Respond to the following:
“Lights turn on so quickly after you flip the
switch because electrons move very quickly.”
Drift speed
Turn & Talk with your table partner
…The scholar with the bigger shoe size
Define drift speed
… The scholar with the smaller shoe size
Respond to the following:
“Lights turn on so quickly after you flip the
switch because electrons move very quickly.”
Direct Current (DC) electric circuits
• a circuit containing a battery is a DC circuit
• in a DC circuit the current always flows in the same
direction.
• Current flows from + to –
• Electrons flow the opposite
direction
Duracell
+
Alternating Current (AC) Circuits
AC movement of electrons in a wire
_
+
• Power outlets supply AC current
• In an AC circuit the current reverses at a frequency of 50
Hz (US) or 60 Hz (Europe)
!! the source of electrons are the free electrons in wire itself !!
When you are shocked by AC current, the electrons that make
the current come from your body. The current makes the
electrons in your body vibrate.
current
How does the voltage and current change in time?
DC
current
time
AC
time
In DC, current and
voltage do not
change direction over
time
the actual voltage in
a 120-V AC circuit
varies between
+170V and -170V
peaks.
Why do power plants produce AC?
• AC can be much more easily stepped up or down
to different voltages through use of a transformer.
• Low voltage is good in a house because it is safer.
• High voltage is useful for transmitting current over
large distances – thinner wires can be used and
there is less loss to heat.
This means that AC is cheaper to transmit and the
plants can be farther from the users.
AC vs DC
Turn and talk with your table partner …
… the scholar who has a birthday earlier in
the month
Identify 3 differences between AC and DC
… the scholar who has a birthday later in the
month
Describe two benefits of transmitting high
voltage current
In the mid-nineteenth century, G.R. Kirchoff
(1824-1887) stated two simple rules using the
laws of conservation of energy and charge to
help in the analysis of direct current circuits.
These rules are called Kirchoff’s rules.
Kirchoff’s rules
1. Junction rule – conservation of charge.
‘The sum of the currents flowing into a point in a circuit
equals the sum of the currents flowing out at that point’.
I1 + I2 = I3 + I 4 + I 5
Kirchoff’s rules
1. Junction rule – conservation of charge.
‘The sum of the currents flowing into a point in a circuit
equals the sum of the currents flowing out at that point’.
I1 + I2 = I3 + I 4 + I 5
This is a slight alteration to our
‘current is the same everywhere
rule’ that we used before.
It means that current can be split
(or combined) at junctures.
Kirchoff’s rules
1. Junction rule – conservation of charge.
‘The sum of the currents flowing into a point in a circuit
equals the sum of the currents flowing out at that point’.
I1 + I2 = I3 + I 4 + I 5
2. Loop rule – conservation of energy principle
‘In a closed loop, the sum of the emfs equals the sum of the
potential drops’.
V = V1 + V2 + V3
Kirchoff’s rules
Emf
= electromotive
force = the potential
difference
1. Junction
rule – conservation
of charge.
supplied by a battery
‘The sum of the currents flowing into a point in a circuit
equals the sum of the currents flowing out at that point’.
This is exactly the same as our rule that voltage is ‘used
up’ across a circuit.
I +I =I +I +I
1
2
3
4
5
2. Loop rule – conservation of energy principle
‘In a closed loop, the sum of the emfs equals the sum of the
potential drops’.
V = V1 + V2 + V3
Circuit Diagrams
Common symbols
ammeter –
measures current
voltmeter –
measures current
Branching
points in the
wire are called
nodes
Circuit Diagrams
You Do: Draw the
schematic of the circuit
Exit Ticket
True / False
1. When a battery no longer works, it is out of charge and must
be recharged before it can work again.
2. The amount of charge that exits a light bulb is less than the
amount that enters the light bulb.
3. Draw the circuit schematic
4. Batteries use ____________ current
5. What is the major difference between AC and DC current?
EC What is the major advantage for using AC current?