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OHM's Low ?
Answers
Materials List
Each group needs:
1 6.3V light bulb
1 lamp base
3 AA battery holders (including wires)
5 alligator clips
two 1.5 volt batteries and/or power supply
multimeter
Ohm's Law Data Sheet
Procedure
Background - Key Facts
Ohm's law is the relationship between voltage, current, and resistance:
V = I x R
Ohm's law equation 1.
Given that the resistance (R) of a device – in this case the light bulb – is constant, if we were to change the current or voltage being provided to the device, we would have an effect on the power.
A light's intensity is proportional to the power (P) supplied to it
Power is given by current (I) multiplied by voltage (V):
P = I x V
Ohm's law equation 2.
By increasing the voltage or current supplied to a circuit, we can increase the power, and therefore increase the intensity of the light.
How can we change current or voltage (I or V)?
We can test parallel and series circuits to see how they affect the intensity of the bulb, or we can test the number of batteries connected to a circuit and the effect of this on I, V, or power.
Batteries connected in a parallel circuit increase the available current (I), but do not change the voltage (V).
Batteries connected in a series circuit cause the voltage (V) to increase, resulting in a corresponding increase in current (I).
With the Students
Introduce the topic. Review definitions of keywords, as well as the topics mentioned in the Background section. Hand out the Ohm's Law Data Sheet and other materials.
Group students. Depending upon the level of students, have them work on their own to develop experimental procedures that test the effect of the alignment of the batteries on voltage and current (and thus light intensity). Other students may follow the sample experimental procedure. Remind students that they are expected to answer the data sheet questions when the experiment is over with the information they gather.
In Groups:
Connect one 1.5 volt battery to a light bulb, as shown in Figure 1. Measure the voltage and current of the bulb (record the data in the table) – be sure to pay attention to the light's intensity. Also draw your own schematic and label each component.
Electrical circuit diagram showing how to connect one 1.5 volt battery to a light bulb.
Figure 1
Next, connect two 1.5 volt batteries in series to the light bulb (see Figure 2). Again, measure the voltage and current, and remember to record your data in the table. Notice the difference in intensity of the light.
Electrical circuit diagram showing how to connect two 1.5 volte batteries in series to a light bulb.
Figure 2
Connect three 1.5 volt batteries in series (see Figure 3). Once again, measure the voltage and current, and record your data.
Electrical circuit diagram showing how to connect three 1.5 volt batteries in series.
Figure 3
Now, connect two 1.5 volt batteries in parallel to the bulb (see Figure 4) and measure the voltage and current (again record the data in your table). Is there an increase or decrease in the light's intensity?
Electrical circuit diagram showing how to connect two 1.5 volt batteries in parallel to a light bulb.
Figure 4
Connect three 1.5 volt batteries in parallel (see Figure 5). Again, measure and record the voltage and current.
Electrical circuit diagram showing how to connect three 1.5 volt batteries in parallel.
Figure 5
Comment on the effect of the number of batteries and their arrangement in the circuit on the power produced, and thus on the intensity of the light.
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