Unit 7
Electric Circuits Current Electricity
the rate at which charge passes a point
Current I is _____________________________________________
Ex. 22 C of charge pass a point in 4.0 seconds. Find I.
I=
Units:
1 coulomb/second = 1 _______________
1 C/s = 1 ____
So the answer can be written I = ________
Physics Reference Tables, page 3: top
the rate at which charge passes a point
Current I is _____________________________________________
I = Δq / t
Ex. 22 C of charge pass a point in 4.0 seconds. Find I.
I=
Δq / t
= 22 C / 4.0 s
= 5.5 C/s
Units:
ampere
1 coulomb/second = 1 _______________
1 C/s = 1 ____
A
5.5 A
So the answer can be written I = ________
fundamental
A
Amperes are ______________________
units. (m___sk)
derived
Coulombs are ______________________
units
What is a coulomb written in terms of fundamental units?
1 C = = A·s
Ex. How much charge passes a point if the current
0.25
3.6
at the point is __________
ampere for ________seconds?
I = Δq / t
0.25 A = Δq / 3.6 s
0.90 A·s = Δq
0.90 C
= Δq
Don't forget that the amount of charge Dq passing a
coulombs, C
point can be written with units of __________________
elementary charges, e
or __________________________________
. The conversion
from one unit to the other is found on pg 1 of PhysRT:
or
Ex.
1 C = _______________________ e
1 e = ________________________ C
How many electrons pass a point in 2.5 seconds if
the current at that point is 0.50 A?
Page 1:
top
Don't forget that the amount of charge Dq passing a
coulombs, C
point can be written with units of __________________
elementary charges, e
or __________________________________
. The conversion
from one unit to the other is found on pg 1 of PhysRT:
6.25 x 1018
1 C = _______________________
e
1.60 x 10-19
or
1 e = ________________________
C
Ex.
How many electrons pass a point in 2.5 seconds if
the current at that point is 0.50 A?
I = Δq / t
0.50 A = Δq / 2.5 s
1.25 C
= Δq
6.25 x 1018 e
1.25 C x ---------------------- =
1C
7.8 x 1018
e
at least
To have current, you need _________________
2 things.
A potential difference
a voltage source)
1. ___________________________
(aka ___________
cell
a/ a ______:
neg. (-)
_________side
or
low
_______
potential
pos. (+)
_________side
or
high potential
_______
wire
wire
two _________________
different metals
voltage
The amount of ____________
depends on the metals used.
more than 1
b/ a battery = _______________cell:
more voltage
more cells  _________________
generator
c/ a ______________
:
Physics Reference Table: page 3 bottom left:
energy
A voltage source V supplies ____________
to a circuit by
an electric field
setting up ___________________________
within the circuit.
low pot.
_______
flow of
electrons
________
( e- )
high pot.
_______
+
V
magnified wire
cross section
flow of
positive
___________
charge
negative "-"
Electrons flow out of the ________________
side of V.
+ side of V.
This is equivalent to flow of ___
+ charge out of ___
atoms
The e-'s collide with _____________
of wire. This absorbs
energy
heats up
electrical __________________
and ______________
the wire.
fast
between
The speed of e-'s ______________
collisions is ____________,
but the
velocity of e- is __________
.
slow
. drift (________________)
or average
"direct"
Batteries supply a constant V  _____________
current
DC
 _______
I
charge moves in
1 direction only
___________________
t
Generators supply a varying V  ________________
alternating
current
AC
 ______
I
one direction
charge moves in _________________
t
direction
charge moves in other
__________________
DC ,
In Regents Physics, we will mostly study _____
AC
but the basic ideas are also valid for ______.
Edison tried to prove that AC was more dangerous
than DC by electrocuting animals. Later, he
helped develop the electric chair.
1903 Topsy dies.
William Kemmler
murdered his common
law wife Tillie with a
hatchet.
“Chaired” on
August 6, 1890
Sizzlin' Sally, Old Smokey, Old Sparky, Yellow Mama,
and Gruesome Gertie.
complete
2. A ________________
circuit
Ex:
battery
+
switch
Using circuit symbols:
V
light
open
no
Switch up  ___________
circuit  ________
current
"complete"
Close the switch  ____________
closed circuit  _____________
current
charge
 __________
flows  ______________
Can you have voltage without current?
yes
Can you have current without voltage?
no
ammeter
Current I is measured with an _________________,
which
digital multimeter
is often part of a DMM (______________________________
).
Its symbol is:
wire
A
wire
In an electrical circuit, ammeters are connected
"in series"
__________________
. This means the circuit must
ammeter
opened up
be ________________
and the _______________
must
be _____________
into it:
inserted
w/o
Circuit _______
ammeter:
circuit
part 1
circuit
part 2
Circuit _________
with ammeter:
circuit
part 1
circuit
part 3
circuit
part 2
A
circuit
part 3
DMM
voltmeter
Voltage V is measured with a _________________,
which
DMM
is often part of a _________.
Its symbol is:
V
In an electrical circuit, voltmeters are connected
NOT
"in parallel"
__________________
. This means the circuit is _______
opened up , but the _______________
must be
voltmeter
connected _____________
across two points in the circuit:
Circuit:
V
circuit
part 1
circuit
part 2
circuit
part 1
circuit
part 3
circuit
part 2
circuit
part 3
Ammeters measure the current that passes ___________
through
a part of the circuit, in other words, the amount of
charge
through it.
___________
each second that passes ____________
potential difference
Voltmeters measure the ____________________________
from one side of a part of the circuit to the other side.
"across"
This is called the voltage _____________
the circuit part.
energy
work
It represents the ____________
or _____________
needed to
coulomb
force each ________________
of charge through.
In symbols:
V
circuit
part
in parallel
I
A
in series
pot. diff.
affect the
Ideally, neither ammeter nor voltmeters ______________
circuit in which they are placed , but in reality they do.
________________________________