Download Circuits and Ohm’s Law

Circuits and Ohm’s
Law
Objectives:
1. To gain an understanding of Ohm’s Law.
2. To compare and contrast the movement of
current through a series and parallel circuit
based on the circuits power supply and
resistance.
Current (I) – the amount of charge that flows by
an area in a unit of time
Current flows from the positive (+) terminal to the
negative (-) terminal of a battery. Electrons flow
from – to +
Measured in Amperes or Amps with an Amp meter
A
Voltage
Voltage (V) - the difference in energy per unit of
charge. It is caused by an unbalance of charge, and it
is the push that drives electrical current. Without it,
electrons will not flow.
Measured in Volts (V) with a Voltmeter
Symbol
V
Resistance
Resistance (R) - Resistance is the value assigned to a
specific conductor that indicates its degree of
resistance to the passage of a current.
Measured in Ohms (Ω) = 1 volt/1 amp
Different objects resist the flow of current more or
less.
The less resistance, the faster the current will flow.
The more the e- want to flow (voltage), the faster the
current is.
Ohm’s Law
The amount of current (speed of charge flow) depends
on how badly the e- want to get to the other terminal
(voltage) and what is in their way to slow them down
(resistance).
This concept is better known as Ohm’s law.
I = V/R
or
V = IR
S-e-r-i-e-s C-i-r-c-u-i-t-s
When circuit elements are arranged in such a
way that there is no branching, as in the next
slide, the various devices are said to be
connected in series.
The basic property of this type of circuit is
that the current is the same in all parts of the
circuit.
IT = I1 = I2 = I3 = ….
• All electricity must go thru all three resistors.
• If one resistor is turned off, all electricity is off.
• The more resistors, the higher the total resistance.
• Each resistor uses some of the total voltage of the
power source.
• Each resistor affects the others.
R= 50Ω
R= 50Ω
R= 50Ω
150 Volts
• Each resistor slows down the electricity (current).
• Thus, the resistance total equals the sum of all resistors.
RT = R1 + R2 + R3 …. = 50Ω + 50Ω + 50Ω = 150Ω
IT = I1=I2=I3 …. I = VT/RT = 150V/150Ω = 1 Amp through out the
circuit
VT = V1 + V2 + V3 … V1 = I1R1 = 1 Amp x 50Ω = 50V
Therefore, VT = 50V + 50V + 50V = 150V, which is the voltage the
battery can provide.
Parallel Circuits
A circuit of this type, where the current divides
into two or more branches, is called a parallel
circuit.
The total current is the sum of the currents
through the individual components.
 VT =  V1 =  V2 =  V3 = ……
• Electricity may go thru any of the three resistors.
• If one resistor is turned off, the others still work.
• The more resistors (branches) that are on, the lower the
total resistance.
• Each resistor has the total voltage of the power source.
• Each resistor has its own circuit.
R= 50Ω
R= 50Ω
R= 50Ω
V=150V
• Current is given three different routes to take (Thus, RT is less than
the individual resistances.)
1/RT = 1/R1 + 1/R2 + 1/R3 + ….. 1/50Ω + 1/50Ω + 1/50Ω = 3/50Ω ; RT =
16.7Ω
VT = V1 = V2 = V3 = ….. 150V
IT = I1 + I2 + I3 + ……. I1 = V1/R1 = 150V/50Ω = 3 Amps ; 3Amps +
3Amps + 3 Amps = 9 Amps = IT
Ohm’s Law Practice
1. Complete the Ohm’s Law Practice
handout
2. Use your notes.
3. Show your work.