Name ____________________________________ LR <?xml:namespace prefix = o ns = \"u
ID: 2120169 • Letter: N
Question
Name ____________________________________ LR <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
Go to http://phet.colorado.edu/en/simulation/circuit-construction-kit-ac
and click on Run Now.
1. Construct the circuit shown to below.
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2. What is the unit of the quotient of inductance and resistance? Show your work below.
time =
3. The quotient of L and R is called the time constant. Adjust the time constant of the circuit to one second. Record the value of inductor and bulb
Explanation / Answer
It depends on the internal Resistance of the source. The circuit made up by the bulbs in parallel is under the potential difference U between the ends of the source which is a decreasing function of the current I furnished by the source. So increasing the number of bulbs you increase the current decreasing U. The result is that the brightness of each bulb decreases depending on the magnitude of the internal resistence of the source. Knowing that the brightness of a bulb is proportional to I^2 you can evaluate exactly that decrease.
Let n be the number of the bulbs, R the resistence of a single bulb, E the electromotive force of the source and r its internal resistence. In accordance with Kirchhoffs' law we have
E=rI+IR/n
where from
I=E/(r+R/n)
and you can see that increasing n I decreases.
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