Regents Physics

1
Regents Physics

• Parallel Circuits
• Ohms Law in Parallel Circuits

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Parallel Circuits
Summary 1. The potential drops of each branch
equals the potential rise of the source. 2. The
total current is equal to the sum of the
currents in the branches 3. The inverse of the
total resistance of the circuit (also called
effective resistance) is equal to the sum of
the inverses of the individual
resistances.
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Parallel Circuit and Ohms Law
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Voltage in a Parallel Circuit

• What is the voltage drop across the resistor and
  light bulb?
• Draw a voltmeter that would measure the potential
  difference across the resistor only

Answer 12 VOLTS
V
12 V cell
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Current in a Parallel Circuit

• Current in divided in the branches
• Resistance of individual resistors determines how
  much current will flow through it

• Question What has higher resistance
• the resistor or the light bulb?
• Draw an ammeter measuring
• the current through the light bulb
• the total current in the circuit

12 V cell
e-
e-
e-
e-
e-
e-
6
Equivalent Resistance

• A short-cut method to using the equation
• Find the average of the resistors
• Divide by number of resistors

is the same as
is the same as
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Equivalent Resistance cont

• More than 2 resistors

is the same as
5712 24 24/3 average 8 8/3 resistors
between 2 - 3
is approximately
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Example of a Parallel Circuit
1) Find current flowing through each
resistor 2) Find the total current flowing
in the circuit 3) Find the equivalent
resistance of the circuit
R1 2 ?
R2 3 ?
R3 6 ?
12V