PHY 2054 Midterm: 2054_Fall12_Exam2-solutions

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turquoisegnu128

31 Jan 2019

School

University of Florida

Department

Physics

Course

PHY 2054

Professor

All

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Document Summary

Exam 2 solutions: resistors of values 8. 0 (cid:1), battery. Which resistor dis (cid:1), 12. 0 (cid:1), and 24. 0 (cid:1) are connected in parallel ac dissipates the greatest power? across a fresh uts resistances at the same voltage. A parallel connection puts resistor is given by v2/r: a series rc circuit has a t a voltage of 50 v and the the switch is 500 ma. What is the charge on the closed: 0. 43 c. The current is i = (v/r) ex the time constant, we get 1 leads to q = 0. 43 c: 2. F = ma or a = f/m gives y forces are equal. But f = md/mp = 2: there is a current i flowin square loop of wire that is magnetic field b is toward loop has length l, then the loop is: a ibl. Her magnitude l2 and direction into th citor q = cv [1-e(-t/ )] with = rc.

Related Questions

An uncharged 30.0Î¼F capacitor is connected in series with a25.0 Î© resistor, a DC battery, and an open switch. The battery hasan internal resistance of 10.0 Î© and its open-circuit terminalvoltage in 50.0 V. The leads have no appreciable resistance. Attime t=0, the switch is suddenly closed. What is the maximumcurrent through the 25.0 Î© resistor and when does it occur(immediately after closing the switch or after the switch has beenclosed for a long time)? What is the maximum charge that thecapacitor receives? and when the current in the circuit is 0.850 A,how much charge is on the plates of the capacitor?

i know its confusing, I just dont know where tostart.....

This set of problems is designed to help you prepare for the lab oncapacitors. Here are some things you should know.
The charge on a capacitor is proportional to the voltage. Theconstant of proportionality is the capacitance:
q=VC.
The simplest type of capacitor is a parallel plate capacitorconsisting of twoparallel conducting plates...DUH. If the plateseach have area A and
are separated by a distance d, the capacitance will be
C=Ke0A/d,
where e0 is the permittivity of free space (you measured that lastweek) and K is the dielectric constant of what ever material isbetween the plates. If the space between the plates is filled withvacuum, the dielectric constant is exactly 1. Air is pretty darnclose to 1.
When a capacitor is charged in a series circuit with a resistor,the charge builds up with time. Consider the circuit below.

When the switch, S, is thrown to position A, the battery, withvoltage V0, will supply a current through the resistor, R, thatcharges the capacitor C. The voltage across the capacitor at anygiven time is given by
V=V0(1-e-t/RC).
The product RC is known as the time constant. After waiting a timeequal to 1 time constant, the voltage on the capacitor is(1-e-1)=0.632 of V0. After 5RC the capacitor is nearly fullycharged and has a voltage of 0.993V0. Eventually, the voltagebuilds up to V0.
When the switch is thrown to position B, the capacitor willdischarge through the resistor. The voltage as a fuction of timewill be given by
V=V0(e-t/RC).
After a long enough time, the capacitor will fully discharge theresistor.

1. [1pt]
A parallel plate capacitor has plates with length and width of 5.7cm and are separated by 7.0 mm. The capacitance is measured to be1.479Ã10-11 F. What is the dielectric constant of the materialbetween the plates?

Correct, computer gets: 3.60

2. [1pt]
Consider a series circuit like the one shown above with a resistorof R=80. kilo-ohms and a capacitor of C=8.0 uF. What is the timeconstant of the circuit?

Correct, computer gets: 0.64 s

Hint: Don't forget to convert to Farads and ohms from uF andkilo-ohms.
3. [1pt]
If the battery has a voltage of 12 V, what is the voltage acrossthe capacitor after the switch has been in position A for 2 timeconstants?

Correct, computer gets: 10.38 V
4. [1pt]
What is the final charge on the capacitor after a long time?

Correct, computer gets: 9.60E-05 C
5. [1pt]
Now let's say that the capacitor has been fully charged and wethrow the switch to position B. How long will it take for thevoltage on the capacitor to be 0.891 V?

6. [1pt] What is the charge on the capacitor at this time?

Answer: ____________