SCED 322 - cwuphys106

10/30/14 Series and Parallel
 Science video: Plant-e: plants generate electricity
 Finish one bulb circuits
 Challenge items
 Resistance and Ohm’s Law
 Series and Parallel circuits
 Start building series and parallel circuits
 Circuit activity
 Homework: Electrical Resistance , Series Circuits,
worksheets (first 2 pages), associated readings
Learning objectives
• Given a one wire, one bulb, one battery circuit,
determine whether or not the bulb will light. If it will
not light, explain why.
• Describe the concept of electric potential and
determine where in a circuit a charge has the
greatest electric potential or electric potential
• Describe/diagram how electric potential and
potential energy varies throughout a circuit.
Gravitational PE
Potential Energy
GPE depends on
height and mass
GP depends on
height only
Electric Potential
Electric Potential
Electric Potential depends
on distance only
EP in a circuit
E is the electric field direction, the
“natural” direction for a positive charge
Battery as a charge pump
Electric Potential in
The electric potential drops across each light bulb. The drop
depends on a characteristic called resistance
Discuss Electric Potential
Difference worksheet
Basic electricity activity
• Sketch the battery and bulb
shown on the right in your
• Add a single wire to your
sketch such that the bulb
would light if these were real
• Briefly explain why your bulb
would light.
Basic electricity activity
Suppose you had to explain to a friend over the
telephone how to light a bulb. Your friend has one
battery, one bulb, and one wire, but has never lit a
bulb before.
1. Write a description of how to light the bulb. (Your
description should be general enough to work for all
the ways that light the bulb.)
2. Read your description to a partner. Your partner
should try to follow your directions exactly to light
the bulb, pretending that s/he has never lit a bulb
Basic electricity activity
The bulb lights when there is an uninterrupted path
from one end of the bulb, through the battery and
through the wire back to the other end of the bulb.
The bulb will light when:
1) one end of the battery is connected to one metal
part of the bulb.
2) one end of a wire is touching the other metal part
of the bulb.
3) the other end of the wire is touching the end of the
battery not touching the bulb.
This results in a complete circuit.
Lighting a bulb
Go over Electric
circuits worksheet
Challenge questions
• What does the inside of a bulb look like? (The part
behind the metal threads.)
• What happens to the brightness of the bulb when
you add another bulb?
o How many ways can you add another bulb?
• What happens to the brightness of the single bulb
when you add another battery?
o How many ways can you add another battery?
A naked bulb
Ways to add two bulbs
Ways to add two batteries
Resistance demo
How will the resistance
change if I …
• Double the length?
• Cut the length in half?
• Triple the area?
• Decrease the resistivity
by a factor of five?
Resistance and Ohm’s Law
The resistance of a long, thin conductor of length L,
cross sectional area A, and resistivity ρ is:
The unit of resistance is the ohm. 1 ohm=1 Ω = 1 V/A.
The current through a conductor is determined by the
potential difference ΔV along its length:
Two types of circuits – an analogy
Added tollbooths
further restrict flow
Added tollbooths
increase flow
Series Circuits
Parallel Circuits
Circuit activity
• Material: battery holders, one battery, 2 identical
bulbs, 2 bulb holders, about 4 wires.
• Construct 3 different circuits. In each case, note how
the bulb brightness changes as you add a bulb
o 1 bulb
o 2 bulbs in series
o 2 bulbs in parallel
• Compare the brightness of the bulbs in each case
• Describe what happens when you take out a bulb in
each of the three circuits
One minute reflection
• Take a minute to write a brief reflection
of what you learned for the past couple
of weeks. Let these questions guide you.
o What new content did you learn?
o What new skills did you learn
o How can you use what you learned in
the future?
o What questions do you still have?
• You need not answer all of these
questions. Use them if you are having
trouble thinking of something to write.