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ELECTRICITY_2

OHM's Law

 

 After watching this video, try to answer the following test:

OHM's Law test

If you need some help, use the following:

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TRANSCRIPTION

0:00
you may pause this video at any time to
0:02
take notes I want to talk about the
0:05
first kind of current flow which is DC
0:08
direct current current flows only in one
0:11
direction and the circuit has polarity
0:15
negative and positive the next kind of
0:18
current flow is alternating current AC
0:21
alternating current means the current
0:24
flows one way and back again many times
0:28
a second in the United States it's 60
0:31
times a second or 60 Hertz Hertz is
0:35
frequency cycles per second in the next
0:40
few slides we're going to talk about
0:41
using simple math to determine if we
0:44
have the right measurements to kind of
0:47
predict what we should have in a circuit
0:49
e is electromotive force which is what
0:54
we measure in volts r is resistance we
0:58
measure in ohms and the symbol for ohms
1:02
is the Omega symbol seen here in red eye
1:07
is intensity and that is our current
1:11
flow that we measure in amps this is
1:15
what we call the direct current Ohm's
1:17
law wheel with this wheel we can solve
1:21
any DC circuit using simple math for now
1:26
we're only going to focus on three
1:28
different formulas at the one o'clock
1:31
position we have ampars we can determine
1:34
how many amps we should have by dividing
1:38
our volts by our resistance at the four
1:41
o'clock position we can determine how
1:44
many ohms we should have by dividing our
1:47
voltage by our current and we can
1:51
determine how many volts we should have
1:53
by multiplying current times resistance
1:57
to break this down even simpler draw
2:01
this out in your notes here is how we
2:04
use this very simple wheel that we
2:07
created by knowing two values we can
2:11
calculate the unknown
2:12
value by covering up the unknown value
2:16
we've created a multiplication I times
2:19
are so let's say we have four amps and
2:24
30 ohms the answer would be 12 volts 4
2:30
times 3 is 12 let's say we want to
2:35
figure out how many amps are going to
2:37
flow through our circuit we take our
2:40
voltage and divide it by our resistance
2:43
when we cover up our unknown value we've
2:45
created a division problem so let's say
2:49
we have 10 volts and 2 ohms what is our
2:53
amperage our amperage is 5 amps let's
3:01
say we would like to calculate how much
3:03
resistance a device exhibits on our
3:06
circuit we would cover up the unknown
3:10
value which is the r4 resistance we've
3:13
created another division problem he / I
3:17
so let's say again we have 10 volts and
3:21
5 amps how much resistance do we have in
3:25
our circuit the answer is 2 ohms
3:29
remember the symbol for ohms is the
3:32
Omega symbol shown at the bottom of this
3:34
picture remember I said using this wheel
3:38
allows us to solve any formula in a DC
3:42
Circuit everything in yellow is how we
3:45
can calculate amperage we use this
3:49
formula e / r to solve for amperage or I
3:55
this part of the wheel gives us three
3:58
ways to solve for voltage or e we use
4:03
this formula I times R to solve e or
4:07
volts this part of the wheel gives us
4:11
three different ways to solve for ohms
4:13
or resistance we used this formula e
4:17
over i equals R or ohms how much
4:22
resistance is in the circuit
4:24
the part of the circle we haven't
4:26
discussed yet is wats the definition of
4:30
watts is heat dissipated wats equals
4:34
power and the symbol for wats can be w
4:38
or P to remember how to calculate wats
4:42
remember the word pi p IE p or wats
4:48
equals I times e current times voltage
4:53
equals wats here is the part of the
4:57
wheel where we can calculate watts there
5:00
are three different formulas to find
5:02
wattage the formula that we just
5:06
discussed and that you should know right
5:08
now is from the word pi p equals I times
5:13
e remember watts is heat dissipated a
5:18
hundred watt light bulb feels hotter
5:21
than a 20 watt light bulb

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