Download Lab Instructions - Ohmmmmm, Ohmmmmm

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Lab Instructions: Ohmmmmm, Ohmmmmm
Purpose: To study the circuits formed by connecting batteries and lamps in series and in parallel and
seeing how that affects Ohm’s Law
Materials: two 1.5V lamps
two 1.5-volt batteries
five test leads
switch
resistors (2, 5 & 10 ohms)
battery charger with ammeter
Part I: Lamps in Series and Parallel
Background: When a battery is providing electricity to a lamp and the lamp is lit, you can be assured
that you have what is known as a closed circuit. Electrons travel from one terminal of the
battery through the lamps and back to the other terminal of the battery. In an open circuit,
electrons do not travel between the terminals of the battery.
A. A lamp connected to a battery represents a simple series circuit. Using three test leads, connect the
1.5-volt battery, an open switch and one lamp (1.5-volt). The switch should always remain open
while all connections are made to prevent the bulbs from blowing if you connect the circuit
incorrectly.
Close the switch and describe the brightness of the bulb in Table 1. (You really need to compare with
step B)
B. Add another lamp, in series, to your circuit. You now have a series circuit containing a battery,
switch and two lamps.
C. Compare the brightness of two bulbs to the brightness of one bulb in series. Record your
observations in Table 1.
D. Unscrew one bulb. Record your observations in Table 1.
E. Remove the second lamp connected into the circuit in step B and reconnect your simple circuit.
Connect the second lamp into the circuit in parallel. Compare the brightness with the two bulbs in
series. Record your observations in Table 1.
F. Unscrew one bulb and record your observations.
Part II: Batteries in Series and Parallel
G. To gain an idea as to how bright one battery will cause a lamp to glow, connect one 1.5V battery, a
switch and one lamp in a circuit. (same basic circuit connected in step A)
H. Observe the brightness of the bulb and record your observations in Table 2. (Again, you actually need
to connect step I to compare.)
I. Connect two 1.5V batteries in series with the switch and lamp. (Make sure the nubs of the two
batteries face the same direction.)
J. Close the switch and observe the brightness of the bulb. Record your observations.
K. Disconnect one of the batteries and record what happens in Table 2.
L. Reassemble your basic circuit. Connect the second 1.5V battery in parallel with the switch and lamp.
M. Repeat steps J and K for the parallel arrangement.
Part III: Ohm’s Law (demonstration)
Background: In this demonstration you will discover the relationship between current, voltage (potential
difference), and resistance. Current is the movement of charge in a conductor and is
measured in amperes. A battery has a difference of potential energy between the positive
and negative terminals. This difference in potential energy is called the potential
difference. The potential difference is measured in volts. In our demonstration we are
using a battery charger instead of a battery. Resistance is a measure of how difficult it is
to move electrons through a conductor. Resistance is measured in ohms ( ).
N. In this demonstration, your teacher will connect a simple circuit consisting of a 2 ohm resistor, a
battery charger, and a switch. The battery charger sill be set at six volts, and the current will be read
from the ammeter on the battery charger. For each resistor record the readings for current (from the
ammeter) and potential difference (from the battery charger) in Table 2.
O. Change the potential difference to 12 volts and record the readings using the 10 ohm resistor.
P. Multiply each current reading by the corresponding resistor reading in the data table. Record this
product in the column labeled Potential Difference (calculated).
Q. Turn in this instruction sheet and answer your questions.