STAO On Line workshops

Contents

Home

Overview

Organizing Your Lab

Lesson 1
A Simple Electric Circuit

Lesson 2
A Series Circuit

Lesson 3
A Parallel Circuit

Lesson 4
Cells & Batteries Sources in Series and Parallel

Lesson 5
Resistance - Ohm’s Law

Lesson 6
Canadian Electricity Alternatives

Course Facilitator & FAQ's

Expectations

Acknowledgements

Lesson 3: A Parallel Circuit

Downloadable student notes (.doc .wpd .pdf )

Downloadable answers to student notes (.doc .wpd .pdf )

Modeling A Parallel Circuit

Background

Wooden Block Model

With the negative box at shoulder height and the positive box at waist height (a one volt battery), two lines of student conductors are formed with a bulb about half way along each wire. Have the student conductor at the branch pass the blocks first to one then to the other branch of the circuit. Ammeters can measure the current along each branch of the circuit and at the battery.

Mention that the current through the student load is related to how fast the load spins. If the energy drop across the load is the same as , then the load spins at the same speed. Therefore the current through each load stays the same regardless of the number of loads in parallel

The teacher can sort out the dilemma of the Junction conductor by saying that when the order "PASS" is given, the blocks are passed down branch "A" of the circuit. When the instructor says "AND", the blocks are passed down branch "B" of the circuit. Start with a slow cadence of "Pass And Pass And Pass ….." then speed up gradually

Demonstration View Parallel Circuit / Styrofoam Cup Demonstration video
Get a few large styrofoam coffee cups. Fill one with water and hold it over a sink. Use a pencil to poke a hole in the bottom of the cup so that water leaks out. Use a rubber hose connected to a tap and held by a retort stand, to act as a battery. It gives the water energy by raising it to the height of the cup. Be sure the students can see the water fall into the cup. Compare the rate the water enters the cup to the rate it leaks from the cup.

Now poke another hole in the cup.

Some questions:

What happens to the rate the water leaves the cup?
What must be done to keep the level of the water in the cup constant?
Does each additional hole affect the rate the water leaks from the others?

Now poke another hole in the cup and ask these questions again.

Each hole acts like another "bulb" which leaks current to the lower potential.

Observations:

Each bulb conducts at the same rate and so gives off the same energy

The current in one branch is less (depending on the number of branches) than the current at the battery terminal (main branch).

Practice Connecting Circuits & Drawing Schematic Diagrams

Once again the student learns to keep all circuit components in the same relative position with these practice questions. The positioning of the ammeters between the light bulbs and the junction points of the branch circuits is very difficult for some students.

REALITY CHECK - Wiring Real Circuits