Download Circuits - cottonphysics

Circuits
•Series
•Parallel
Ohm’s Law
V = IR
• V = Voltage (Volts)
• I = Current (Amps)
• R = Resistance (Ohms)
Series
Circuits
•Have only one path
•The battery is represented by the escalator which raises
the charges to a higher energy level (voltage source).
•As the charges move through the resistors (represented by
the paddle wheels) the charges do work (J/C), and
subsequently, lose energy (experience a voltage drop).
•The charges do more work as they pass through the larger
resistor.
•By the time each
charge makes it back to
the battery, it has lost
all of the energy given
to it by the battery.
•The sum of the potential drops (voltage drops) is
equal to the potential rise (voltage source) from the
battery.
•This demonstrates that a charge can only do as
much work as was done on it by the battery.
Series Circuits
1. The sum of the potential
drops equals the potential
rise of the energy source
Vtot = V1 + V2 +…
2. The current is the same
throughout the circuit
Itot = I1 = I2 = …
3. The total resistance of the R = R + R + …
tot
1
2
circuit (equivalent
resistance) is equal to the
sum of the individual
resistances.
Symbols Used in Drawing Circuits
R1 = 2 ohms
R2 = 3 ohms
R3 = 1 ohm
VB = 12 V (voltage source)
• Find the equivalent resistance of the circuit.
• Find the current of the circuit
• Find the voltage drop at each resistor
• Draw a circuit that has:
– 12 volt battery source
– 3 Ω resistor
– 2 Ω resistor
• Calculate the equivalent resistance in the circuit
• Calculate the current in the circuit
• Calculate the voltage drop across each resistor
Parallel Circuits
Voltage
• The potential drops
of each branch
equal the potential
rise of the source.
• The voltage is the
same through
each resistor
Current
• The total current is
equal to the sum of
the currents in the
branches
• The current can
branch into new
pathways that can
allow different
currents per path.
Resistance
• The total resistance of the
parallel circuit is equal to
the inverse of the sum of
all the inverse resistance
combined
• Straw comparison!!
Parallel Circuits
If your voltage source = 12 V,
what is the voltage across
each resistor (assume they
have the same resistance)?
What is the voltage across
each resistor if all three
resistors are different?
Current in Parallel Circuits
• Current is divided in the branches
• Resistance of individual resistors
determines how much current will
flow through it
• So – essentially, the currents will
be different through each of the
resistors.
Current in Parallel Circuits
1) Find the equivalent resistance of the circuit
2) Find the total current flowing in the circuit
3) Find the current flowing through each resistor
VB = 12 V
R2 = 2 Ω
R1 = 3 Ω
R3 = 1 Ω