Relationship between Voltage and Current
1. Connect a 1.5 V cell (battery) to a switch and a light bulb rated at about 5 V to 6 V. Turn the
switch on and observe the glow.
2. Repeat step 1 using two cells and three cells connected in series. Observe the glow of the
bulb for each set up.
3. Compare the brightness of the bulb using one cell, two cell, and three cells.
4. Knowing that brightness of the bulb indicates the amount of current, what effect does
voltage have on current?
Answers
Batteries & Bulbs 1
Batteries & Bulbs
SIMPLE CIRCUITS
An electric circuit is a complete conducting path for an electric current. When the circuit is connected to a
battery, electrons flow from the negative terminal of the battery, through one or more electrical devices, and
then back to the positive terminal of the battery. There are different ways in which circuits can be wired, and
these ways can be described with words or by symbols that are widely known and used. Some of these
symbols are illustrated belin the current is observed when the brightness of the bulb increases. If any series bulb is unscrewed, an open
circuit is created and no current exists.
Each device placed within the circuit provides a resistance to the electrons flowing through the wire. Some
devices apply greater resistance than others. As the number of devices placed within one series circuit
increases, the resistance also increases. In a parallel circuit, as electrical devices are added the resistance
decreases.
I. MAKING THE CONNECTION
Use one cell, one bulb (no base), and one piece of connecting wire
(called an electrical lead) make the bulb light. Using the diagrams of
the cell and bulb (illustrated to the right), sketch your orientations
below. There are four possible orientations of the cell and battery that
make the bulb light.
1 2 3 4
II. PLACING CELLS IN SERIES
Using the 4-cell battery pack, orient the metal terminals so that
only one cell is connected. Using two pieces of electrical leads,
connect one bulb (with base) to the battery to make it light.
Using the symbols (illustrated on the top of the first page) for
the battery (two cells) and bulb, draw a diagram of this circuit
in the box to the right. Indicate the path of the electrons.
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Batteries & Bulbs 2
Increase the number of cells in series used
to light the bulb and record your observations
concerning the brightness of the bulb when the
number of cells (voltage) in the circuit increases.
III. PLACING BULBS IN SERIES
Place two bulbs in series by connecting the two bulbs with an additional electrical lead between the bulbs.
Start with one cell and record the brightness of the bulbs. Increase the number of cells in the circuit and
record your observations as the voltage in the circuit increases. Unscrew one of the bulbs and record your
observations. A circuit diagram of two cells and two bulbs in series is shown below
Place three bulbs in the circuit by connecting the bulb with another electrical lead. Unscrew one of the bulbs
and record your observations. Vary the voltage within the circuit and record your observations. Sketch a
diagram of the circuit.
IV. BULBS PLACED IN PARALLEL
Using two cells, two bulbs, and four electrical leads, connect the two bulbs in parallel as shown in the
diagram. Note the brightness of the bulbs and compare this brightness with the two bulbs connected in series.
Unscrew one the of the bulbs and record your observations. Sketch a diagram of this circuit diagram.
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Placing cells in series increases the
voltage in the circuit by 1.5 V for each
cell. Increasing the voltage increases the
brightness of the bulb.
When a bulb in a series circuit is
unscrewed all bulbs in the circuit go out.
Increasing the number of bulbs in a series
circuit decreases the brightness of the
bulbs. In a series circuit, the voltage is
equally distributed among all of the
bulbs.
Bulbs in parallel are brighter than bulbs
in series. In a parallel circuit the voltage
for each bulb is the same as the voltage
in the circuit. Unscrewing one bulb has
no effect on the other bulb.
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Batteries & Bulbs 3
Using four cells and three bulbs, and two additional electrical leads, connect three bulbs in parallel. Note the
brightness of the bulbs and compare this brightness with three bulbs connected in series. Unscrew one of the
bulbs and record your observations. Sketch a diagram of the circuit.
V. CELLS PLACED IN PARALLEL
Using two cells, two long aluminum strips, and two rubber bands, connect the two cells in parallel so that the
two positive terminals are connected together and the two negative terminals are connected together.
Connect a light bulb to the battery using two leads. Compare the brightness of the bulb produced by two
cells in parallel with two cells in series.
A bulb connected to two cells in series is brighter than connected two to
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Answer:
If the bulb and the battery are the sole components in the circuit, the voltage across the bulb equals the voltage across the battery in a series circuit. The voltage across a bulb is NOT the same as the battery voltage in a series circuit if there are any additional loads in series with the bulb.
Explanation:
- The voltage in the circuit is increased by 1.5 V for each cell when cells are connected in series. The brightness of the bulb is increased by increasing the voltage.
- The entire circuit goes dark when one bulb in a series circuit is unscrewed.
- As the number of bulbs in a series circuit grows, the brightness of the lamps dims. In a series circuit, the voltage is distributed evenly among all of the bulbs.
- Bulbs connected in series produce more light than bulbs connected in parallel. In a parallel circuit, each bulb receives the same voltage as the others. The removal of one bulb has no bearing on the removal of the other.
Batteries and Light Bulbs 3
- Connect three bulbs in parallel using four cells, three bulbs, and two additional electrical leads. Take note of the bulbs' brightness and compare it to the brightness of three bulbs connected in series. Unscrew one of the bulbs and make a note of your findings.
- Connect the two cells in parallel using two cells, two long aluminum strips, and two rubber bands such that the two positive terminals are connected and the two negative terminals are connected.
- Using two leads, connect a light bulb to the battery. Compare the brightness of the bulb produced by two parallel cells against two series cells.
- A bulb linked to two cells in series produces more light than two bulbs connected in parallel.
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