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Unformatted text preview: LORATION
WARNING: A short circuit is what happens any time a very low-resistance path (like
a wire, or other piece of metal) is provided between points in a circuit that are at
different potentials, like the terminals of a battery or power supply. Short circuits can
destroy equipment and injure people! Always avoid short circuits in other circuits!
Short circuits damage equipment by causing larger currents in a circuit than they are
designed for. Only apply the short circuit for a small amount of time.
Build Circuit II. What happens to the brightness of bulbs B and C when you place a
wire across bulb B? How did the current through C change? How did the current
through B change? Did the current through point 1 change? If so, in what way? Did
the wire across bulb B get warmer? Explain your answers.
Build Circuit III. What happens to the brightness of bulbs D and E when you place a
wire across bulb E? Did the current through D change? Did the current through E
change? Did the wire across bulb E get warm? What would be the brightness of a bulb
inserted in the circuit at point 1? Explain your answers.
Build Circuit I. Place a wire across the bulb. What happens to the brightness of the
bulb? Hold on to the wire that is across the bulb. Is it getting warmer? How did the
current through the bulb change? How about the current coming out of the battery?
Make sure you disconnect the battery when you are done.
Placing the wire across the bulb causes a short circuit and it is called "shorting out" the
bulb. 90 SHORT CIRCUITS – 1302Lab4Prob3 CONCLUSIONS
Did your predictions match your observed results? What have you learned from
experiments, which agreed with your predictions? Draw more conclusions based on
the experiments where your predictions were different from what you observed. 91 SHORT CIRCUITS – 1302Lab4Prob3 92 PROBLEM #4: CHARGING A CAPACITOR (PART A)
You have designed a circuit using a battery and a capacitor to automatically dim the
lights for a theatrical production. However, the lighting consists of many different
kinds of bulbs, which have been manufactured differently, and which consequently
have very different resistances. You need to be able to precisely control the rate at
which the lights dim, so you need to determine how this rate depends on both the
capacitance of the capacitor and the resistance of the bulb. You decide to model this
situation using a circuit consisting of a battery, a capacitor (initially uncharged), and a
resistor, all in series. You will try to ascertain how the current in the circuit changes
Instructions: Before lab, read the laboratory in its entirety as well as the required reading in the
textbook. In your lab notebook, respond to the warm up questions and derive a specific prediction
for the outcome of the lab. During lab, compare your warm up responses and prediction in your
group. Then, work through the exploration, measurement, analysis, and conclusion sections in
sequence, keeping a record of your findings in your lab notebook. It is often useful to use Excel to
perform data analysis, rather than doing it by hand.
Read: Tipler & Mosca Section 25.6. EQUIPMENT
Build the circuit shown using
wires, resistors, capacitors,
accompanying legend to help
you build the circuits. You
will also have a stopwatch, a
light bulb, and a digital
multimeter (DMM). Circuit Read the section The Digital Multimeter (DMM) in the Equipment appendix.
Read the appendices Significant Figures, Review of Graphs and Accuracy, Precision
and Uncertainty to help you take data effectively.
If equipment is missing or broken, submit a problem report by sending an email to
email@example.com. Include the room number and brief description of the
problem. 93 CHARGING A CAPACITOR (PART A) – 1302Lab4Prob4 WARM UP
1. Draw a circuit diagram, similar to the one shown above. Decide on the properties of
each of the elements of the circuit that are relevant to the problem, and label them on
your diagram. Label the potential difference across each of the elements of the circuit.
Label the current in the circuit and the charge on the capacitor.
2. Use energy conservation to write an equation relating the potential differences across
all elements of the circuit. Write an equation relating the potential difference across
the capacitor plates and the charge stored on its plates. What is the relationship
between the current through the resistor and the voltage across it? Are these three
equations always true, or only for specific times?
3. Describe qualitatively how each quantity labeled on your diagram changes with time.
What is the voltage across each element of the circuit (a) at the instant the circuit is
closed; (b) when the capacitor is fully charged? What is the current in the circuit at
these two times? What is the charge on the capacitor plates at these two times?
4. From the equations you constructed above, determine an equation relating the
voltage of the battery, the capacitance of the capacitor, the resistance of the resistor, the
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- Spring '14