Transcript Day-4-Volts-Amps-Resistance

V= I X R
Volt= Amps X Resistance
There is a student sheet to accompany this PowerPoint
VOLTS, AMPS, RESISTANCE
Amps
Volts
Resistance
V=I·R
VOLTS= AMPERES X RESISTANCE
• What do the words mean
Volts- the amount of energy that the charged
particles have.
Amperes (Amps)- the amount of charged particles
that pass a given point in a given time.
Resistance- the amount of difficulty the charged
particles encounter in their movement. Many things
can cause resistance in a circuit, including lengthing
the wire, decreasing the diameter or the wire, or
adding appliances to the circuit.
Calculating V= I X R in Parallel Circuits
Each parallel on the circuit can be figured using V=IR. To find the total amps,
volts, or resistance in the circuit, figure each parallel individually and add them
together.
Amps will be highest where resistance is lowest as shown in the see saw below.
Amps
Volts
Resistance
Use this information to predict the results of the following situations:
1. I have a parallel circuit with two small bulbs and a large appliance.
Which parallel is receiving the least amps and why?
2. My battery is producing 10 volts. I am about to put a light bulb of 10
ohms resistance on the circuit but I need to know how many amps it will draw.
Can you help? (V=IR, R=V/I, I=V/R)
Calculating V= I X R in Series Circuits
1. Finding Amps- Add up total resistance on the line and use V=IR to find
the amount of amps on the line.
2. Finding Volt for each resistance- Once you have the
amount of amps, use V=IR to find the voltage drop for each
individual resistance.
Calculate the number of amps
in this circuit. The battery is
producing 10 volts and each
bulb is 10 ohms of resistance
.3333 amps
Calculate the voltage drop for
each bulb (it will be the same
for all three.)
3.3333 volts
The following picture shows a bulb that is a 10 ohm resistor and a
battery that is 10 volts. Can you figure out how many amps it is
drawing from the battery? Click for an answer
V= IR, so with 10 volts, unknown amps, and 10 ohms of resistance, we can figureV/R= I
10V/10ohms =1 ampere (the voltage drop isn’t exactly 10 but close enough)
Predict the # of amps for one more light in parallel. Click for help.
O.K. Here’s a hint. Use V= IR to figure out the amps
for each parallel circuit. Now think of the different
Did your
work hallways
out? Do for
youstudents
understand?
circuits
as math
different
(amps) to
exit
a building
(the
battery).
know howwhy
many
Look
at the last
pictureDo If
youyou
understand
students
are
each
hallway,
and
howthe
many
hallways
there are
3 in
amps
being
drawn
from
battery?
there are, you can calculate the total # of students.
Then predict for another resistor added of 200
ohms…
Compared to
Adding another 200
ohm resistor barely
changed the number of
amps. Calculate the
number of amps added
if the resistance added
is a wire with resistance
of .0001 ohms. Click for
the answer.
Amps vs. Resistance Analogy
The reason why the number of amps increases so much is because the wire offered very
little resistance. If the volt is constant, the amount of resistance and amps will contrast
each other. If the resistance is high, the amps will be low, but if the resistance is low,
the amps will be high.
Use the analogy of students walking in hallways to remember. The square on the left
represents a gym where the entire school has just gathered for an assembly. Students
are now exiting to their rooms. Notice that because the hallways aren’t very wide, it is
very crowded and students are restricted in their movement. Click once. Now describe
on your student sheet what you think will happen, especially in the high resistance
hallways. Relate to electricity.
High resistance
hallways
Ice-cream shopJust Opened!
Low Free ice cream
resistance
for the next
hallway
5 minutes!
New extra-wide
hallway just built!
Compare each of the three pictures with
the picture before it and below it. The
circled A on the wire shows where the
amount of amps was measured. Discuss
patterns.
Now recall the addition of a low resistance wire. What would this wire be
called? What might happen to the wire with that much current? What
device do we have in our house to protect against this? Would we place
the device at point A, B, C, or D. Why?
A
B
C
D