Series Circuits

1
Series Circuits

• Series circuit a circuit in which all parts are
  connected end to end to provide a single path for
  the current.
• Ammeters are always placed in series

2

• The current is the same through each resistor
• I I1 I2 I3 .
• The total potential difference equals the sum of
  the potential differences across the individual
  resistors.
• V V1 V2 V3 .
• Equivalent resistance resistance of a single
  resistor that could replace a combination of
  resistors
• Req R1 R2 R3 .

3

• Example Four 15 O resistors are connected in a
  series to a 45-V battery.
• a.) Draw the circuit (include an ammeter and
  voltmeter)
• b.) What is the current of the circuit?
• c.) What is the potential difference across each
  resistor?
• Example A 5.0 O resistor and a 10.0 O resistor
  are connected in series and placed across a
  45.0-V potential difference.
• a.) Draw the circuit (include an ammeter and
  voltmeter)
• b.) What is the equivalent resistance of the
  circuit?
• c.) What is the current through the circuit?
• d.) What is the voltage drop across each
  resistor?
• Example A 20.0 O light bulb and a 5.0 O light
  bulb are connected in series and placed across a
  potential difference of 50.0 V.
• a.) Draw the circuit (include an ammeter and
  voltmeter)
• b.) What is the equivalent resistance of the
  circuit?
• c.) What is the current in the circuit?
• d.) What is the voltage drop across each light
  bulb?
• e.) What is the power through each light bulb?

4
Parallel Circuits

• parallel circuit circuit that has multiple
  independent paths along which the current can
  flow . Each component has its own path
• Voltmeters are always placed in parallel.

5

• The sum of the currents in the branches is equal
  to the total current from the source
• I I1 I2 I3 .
• the potential difference across each branch of
  the parallel circuit is the same as that of the
  potential difference supplied by the source
• V V1 V2 V3 .
• the equivalent resistance is always less than the
  resistance of any branch
• 1/Req 1/ R1 1/R2 1/R3 .
• Note Find a common denominator or use a
  calculator.
• The resistance decreases because each new
  resistor provides an additional path for current
  to flow.

6

• When appliances are connected in parallel, each
  additional appliance placed in operation reduces
  the equivalent resistance in the circuit and
  causes more current to flow through the wires.
• fuses a short piece of metal that melts from the
  heating effect of the current, breaks the circuit
  if too much current is flowing, this can prevent
  damage and fire
• A circuit breaker is an automatic switch that
  opens when the current reaches some set value.
  Doesnt need to be replaced.
• Short circuit occurs when a circuit is formed
  that has a very low resistance. The low
  resistance causes the current to be very large.
  If there were no fuse or circuit breaker, such a
  large current could easily start a fire.

7

• Kirchoffs 1st law (Conservation of charge in
  electric circuits) Charge in an electric current
  must be conserved. At any junction in a circuit,
  the sum of the currents entering the junction
  must equal the sum of the currents leaving it.

8

• Example Three resistors of 60.0 O, 30.0 O, and
  20.0 O are connected in parallel across a 90.0-V
  difference in potential.
• a.) Draw the circuit (include an ammeter and
  voltmeter)
• b.) Find the equivalent resistance of the
  circuit.
• c.) Find the current in the entire circuit.
• d.) Find the current through each branch of the
  circuit.
• Example A 20.0 O lamp and a 50.0 O lamp are
  connected in parallel and placed across a
  difference in potential of 50.0-V.
• a.) Draw the circuit (include an ammeter and
  voltmeter)
• b.) What is the equivalent resistance of the
  circuit?
• c.) What is the current of the circuit?
• d.) What is the current through each resistor?
• e.) What is the voltage drop across each
  resistor?
• f.) What is the power used by each lamp?

9

• Example A 16.0 O and a 20.0 O resistor are
  connected in parallel. A difference in potential
  of 40.0V is applied to the circuit.
• a.) Draw the circuit (include an ammeter and
  voltmeter)
• b.) Compute the equivalent resistance of the
  circuit?
• c.) What is the current of the circuit?
• d.) What is the current through each resistor?