Download Section 3

Circuits Lab – Week 3
3.1 – Drawing Circuits
Many of the circuit diagrams in earlier sections sketched the “visual”
appearance of circuits — drawing batteries, bulbs, and wires as they actually
appear. From now on we will draw “schematic” diagrams — using symbols
to represent the circuit components. The battery symbols used in this
manual from now on are shown below.
In the space to the right of the visual circuits, draw the schematic diagram
for the circuits.
The positive terminal of the battery is represented by a long, thin line and a
+ sign. The negative terminal of the battery is represented by a short, thick
line with a – sign.
Additional schematic diagram symbols are shown below.
3.2 – Electric Pressure
Look at the syringe circuit at the front of the room.
Try to compress one side and watch what happens to the other. Try to
compress one side while holding the other side still.
What happens to the air pressure inside the syringe as you decrease the
volume?
Note the difference between the visual circuit on the left and its schematic
diagram on the right.
Do you think the air is trying to expand back out when you compress it?
What evidence do you have?
A battery is a device that has electric pressure, much like the syringe being
squeezed has air pressure. Inside a battery there is a chemical reaction that
separates a substance into its ions. One side of the battery has a high
electric pressure (the positive terminal) and one side of the battery has low
electric pressure (the negative terminal). The pressures don’t equalize
inside the battery because the chemical reaction prevents it. But when the
battery is connected to a circuit, the difference in electric pressures causes
charge to flow from an area of high pressure to an area of low pressure.
1.) The battery maintains the highest pressure difference in a circuit. Color
the positive terminal and all the wires connected to it RED. Color the
negative terminal and all the wires connected to it BLUE.
2.) Use only color for a wire (and all the wires connected to it)
3.) Use different colors for each side of a light bulb.
4.) Do not color light bulbs.
Electric pressure is given the name voltage and is measured in volts.
5.) Bulbs of the same brightness will have the same color jump.
3.3 – Color Coding
Why do you think wires are given uniform colors?
Colors can be used to represent electric pressure values in circuits. Colorcoding a circuit enables you to visualize pressure differences. It will help
you to see which light bulbs light and their relative brightness.
The following is the color system that will be used:
Rules for Color Coding –
Practice:
Color Code the following circuits. Then put starburts on each lightbulb.
Add starbursts to the bulbs based on the color difference across each one.
How do you predict the brightness of the bulbs to compare?
Now build the circuit.
How do the brightness of the bulbs compare?
According to the color coding you did earlier, why are the bulbs equally
bright?
3.5 – Series vs. Parallel
3.4 – Different Bulbs in Parallel
Color Code the circuit below.
From Lab 1 you learned that things connected in series have the same
charge flow (current) because they have the same compass deflection.
From 3.4 you have seen that things connected in parallel have the same
pressure difference (voltage) because they have the same color jump.
IMPORTANT!!! :
Series = Same Current
Parallel = Same Voltage
SUMMARY
1.) All bulbs are identical. Rank them in order of brightness.
2.) All bulbs are identical. Rank them in order of brightness.
3.) Things in series have the same ______________________________.
4.) Things in parallel have the same _____________________________.