Download Series and Parallel Circuits 1 - Instructor Outline

Instructor Outline:
Series and Parallel Circuits I
UM Physics Demo Lab 07/2013
Lab length: 70 minutes
Lab objective: Instruct the students about series circuits, parallel circuits, voltage,
current, Kirchhoff’s Loop Rule, Kirchhoff’s Junction Rule, Ohm’s Law and power.
Materials
1 Green multimeter (with leads)
1 battery board
1 alligator lead card
Suggested Demonstrations: None
Exploration stage: 50 minutes – Group Lab-Work
The students build a simple circuit and measure voltage and current. They observe
that current is the same throughout the circuit, but that voltage depends on the
enclosed components. The students then build a two-bulb circuit and measure voltage
and current. They add a third bulb and see how that affects the overall voltage and
current. They then build a two bulb parallel circuit. They measure voltage and current
and then calculate and compare the power dissipated by two bulbs in series and in
parallel.
Summary: 20 minutes – lecture
The concepts of series circuit elements, parallel circuit elements, voltage, current, and
power are reviewed and discussed in further detail.
Kirchhoff’s Loop Rule and
Junction Rule are formally introduced. The connection is made between the Loop Rule
and the conservative nature of the electric force, recalling the conservative nature of
gravity as a previous example. The Junction Rule is compared to the condition of
continuity for a flowing fluid.
Concepts Developed:
1. The total voltage available to a circuit is determined by the number of cells
in series for the source battery.
2. The electric force in a DC circuit is conservative.
3. The sum of the component’s voltages in a series circuit is equal to the voltage
of the source (Kirchhoff’s Loop Rule).
The Loop Rule results from the
conservative nature of the electric force and is equivalent to the statement that
the electric force does no net work over a closed loop path, exactly the same as
for gravity.
4. The current is the same throughout each element of a series circuit.
5. The current is inversely proportional to the number of resistors (bulbs) in
the circuit (Ohm’ Law).
6. The current divides in a parallel circuit, but the total current must be conserved
(continuity, charge conservation and the Junction Rule).
7. The voltage across each component in a parallel circuit is the same and equal
to the source voltage. This implies that the voltage across each element in a
series circuit is less than that for a parallel circuit for the same source potential
(battery voltage).
8. Power/brightness is the product of the voltage across a bulb and the current
flowing through it.
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