H. E. Smith | Spring 2000 |
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Physics 1B - Tutorial #7 |
One wire attaches to the contact at the center of the base - note that it is surrounded by insulation. The other wire attaches to the metallic side of the bulb base. On the basis of the observations that we have made, we will make the following assumptions:
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Starting with these assumptions, we will develop a model that we can use to account for the behaviour of simple circuits.
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Using the 2 bulbs in series add an extra battery in series with the first so
that their voltages both act in the same direction. Draw the circuit you have
created.
You have doubled the voltage and doubled the resistance; the current/brightness of each bulb in the 2 battery/2 bulb circuit should be the same as in the 1 battery/1 bulb circuit.
With two batteries you have doubled the current and the voltage through a single bulb, resulting in power (P = VI = I2R) 4X larger.
If the batteries have the same voltage the net potential difference across the two batteries is zero; there will be no current. | ![]() |
Set up a two-bulb circuit with identical bulbs so that their terminals are
connected together as shown. Bulbs connected together in this way are said
to be connected in parallel.
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What can you infer about the total resistance of a circuit as the number of
parallel branches is increased or decreased?
Resistance for n parallel resistances will be R/n.
If the 2 batteries had slightly
different voltages (maybe one is a little flat) would you expect the bulbs to
change a little in brightness as the second battery is added?
If the second battery has a larger voltage, both bulbs will have this larger
p.d. across their terminals, thus higher current and will be brighter.
Would the 2 batteries in parallel be able
to light the bulbs for a longer period of time than a single battery?
Yep, twice as long.
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Set up the circuit and check your predictions. If your observations and measurements are not consistent with your predictions, resolve the inconsistencies. |
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Tutorial #6
Tutorial #8