PreLab – Capacitors Name:
Q = CV Capacitors: Parallel: Ceq = C1 + C2 + … + CN Series: 1/Ceq = 1/C1 + 1/C2 + … + 1/CN
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1. Capacitors consist of two ____ (the plates) that are given ______ charges.
2. T / F Hint: Check your lab manual In today’s lab, if you place a capacitor in the reverse direction nothing will happen. |
3. Potential energy is stored in many forms. Mark all of the following that are valid forms of stored potential energy. (note: consult your lecture book) a. Magnetic fields as in capacitors b. Gravitation potential energy c. Magnetic fields as in inductors d. Chemical energy as in batteries e. Electric fields (or electro-static) as in capacitors
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4. In Figure A (parallel) of your lab manual, given the capacitance of C1 = 18 Farads and C2 = 6 F, what is the Ceq? |
5. In Figure B (series), the potential difference is 3.0 Volts measured across C1, where C1 = 18 F and C2 = 6 F. What is the voltage drop about C2?
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Graphing portion of Part C (Using the 22 mf capacitor) -.007, 1.4472 |
Note: A capacitor is essentially “charged” after 5 RC time constants have been achieved (if needed use eq 8 to verify).
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6. As in Part C of your lab, graph the given data and solve for the time constant, τ = RC, the voltage as the RC circuit starts discharging, Vmax.
y = m x + b ln(V) = (-1/τ) t + ln Vmax
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7. (a) If the resistor is 30 kΩ (kilo-ohm) and the capacitor is 40 μF (micro-farads) how much time has expired to achieve 5-time constants?
(b) What percent of Vo remains after three RC time constants have expired while discharging a capacitor? Eq 8: V = Vo e-t / RC
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V |
3.00 |
2.50 |
2.00 |
1.50 |
1.00 |
0.50 |
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t (sec) |
51 |
76 |
107 |
149 |
208 |
307 |
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Use LineFit (or your favorite method) to graph the above data
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Slope:
y-int
x-int |
τ = |
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Vmax = |
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