Electrical Circuits Lab
Ben Franklin Academy Physical Science
Introduction
Electricity cannot flow away from a source (battery) unless there is an
unbroken pathway to carry the current back to the source. This unbroken
pathway is called an electrical circuit. A break or opening in an electrical circuit,
no matter how small, will prevent electrical energy from leaving the source.
Electrical switches are devices that control the flow of electrical energy by
“opening” or “closing” the electrical circuit.
A circuit that provides only one pathway for the flow of electricity from the
source back to the source is called a series circuit. In a series circuit, all of the
current flows through each part of the circuit. If the circuit is broken anywhere,
current stops flowing everywhere.
A circuit that provides more than one pathway, or “branch”, for the
electricity to flow is called a parallel circuit. In a parallel circuit only part of the
current flows through each branch. If there is a break in one branch, current
continues to flow in the other branches.
Voltage (V, volts) is a measure of the force available to push electrical
current through the circuit. When voltage equals 0 no current can flow. While a
battery is in use, its voltage decreases. When a battery is “dead”, its voltage
measures zero.
Amperage (A, amperes) is a measure of the rate of current flow in a
circuit. Resistance (R, ohms) refers to the opposition that wires and other
devices placed in electrical circuits offer to the flow of electrical current. In an
electrical circuit, the product of the Amperage x the Resistance equals the
Voltage consumed. This product is called the Voltage Drop. A x R = V drop.
Series Circuits vs. Parallel Circuits
In Series Circuits:
Amperage is the same everywhere in the circuit and is the same as the
amperage of the source.
A(source) = A1 = A2 = A3, etc.
Voltage at source = the sum of the voltage drops in the circuit.
V(source)= (A1*R1) + (A2*R2) + (A3*R3), etc.
When batteries are connected in series the total voltage equals the sum of the
individual voltages of each battery. As a result the rate of current flow is
increased and the combination can do more work that just one battery.
In Parallel Circuits:
Voltage is the same everywhere, and is the same as the Voltage at the source.
V(source) = V1 = V2 = V3, etc.
V(source) = (A1*R1) + (A2*R2) + (A3*R3), etc.
Amperage at the source = the sum of the Amperage in each branch
A(source) = A1 + A2 + A3, etc.
Connecting batteries in parallel does not result in an increase in Voltage. The
rate at which work can be done by the combination is the same as that of a
single battery, but the combination can maintain that rate for a longer time.
Procedure
1. Use two batteries, connecting wires, a switch, and a light bulb to construct
a series circuit.
2. Add another light bulb to your series circuit. Does the added bulb affect
the brightness of the original light bulb?
3. If you disconnect one of your light bulbs, do the other light bulbs in the
circuit go out or stay lit? Why?
4. Is the amperage in the circuit the same everywhere or different depending
on where you are in the circuit?
5. If you were to add another battery to your series circuit, will the total
voltage in the circuit increase or stay the same?
6. Use two batteries, connecting wires, a switch, and a light bulb to construct
a parallel circuit.
7. Add another light bulb to your parallel circuit; does the added bulb affect
the brightness of the original light bulb?
8. If you disconnect one of your light bulbs, do the other light bulbs in the
circuit go out or stay lit? Why?
9. Is the voltage in the circuit the same everywhere or different depending on
where you are in the circuit?
10. If you were to add another battery to your parallel circuit, will the total
voltage in the circuit increase or stay the same? What is the benefit, if any,
to adding an additional battery to a parallel circuit?
11. Check to see if various objects (nickels, pennies, binder clips, etc.)
conduct electricity through the circuit or break the circuit. Record your
predictions and observations below.