Physies 3172 3rd Exam Nevember 22,2017 . 4 The igure below shows two points in a

Question

Physies 3172 3rd Exam Nevember 22,2017 . 4 The igure below shows two points in an electric field. Point i and point 2 is at Ca.Y)-13,10). (The coordinates are given in field is constant with a magnitude of 533 V/m, and is directed paleltotCaleula The potential at point 2 is 1000.0 V. (a) Calculate the potential at point 1.() the work required to move a positive charge of Q-513.0 /C from point 2 to poti in meters.) The to the +X-axis point 1 2. Three capacitors of capacitance Cr-5.00 F, C-5.00 F, and C-100 u are connected to a 10.0 V battery as shown in the figure. (a) Calculate the change on Ch Calculate the voltage across Ca. (c) Calculate the charge on C 3. A power transmission cable is composed of 37 strands of aluminsm wire, each 4 in diameter. The cable is 100 m long and is used to deliver 300 A of current to a commercial power user. Determine. (a) the total cross sectional area of the cable, (b) the resistance of the cable, and (ejthe power lost in the cable before it reaches the user. 4. A capacitor is fully charged by a battery and disconnected. An insulator with dielectric constant k is then inserted into the capacitor. Show how each of the following quantities are changed. (a) capacitance (b) voltage (c) E-field (d) charge on the surface of the insulator. (e) charge on the plates. Fig. 1 C2. nesis Suorez Gorzaez 802-12-7773

Explanation / Answer

2.

Remember:

For parallel combination

Ceq = C1 + C2 + C3 +...............

for series combination

1/Ceq = 1/C1 + 1/C2 + 1/C3 + ............

for 2 capacitors in series it will be

Ceq = C1*C2/(C1+C2)

Using this Information:

C1 & C2 are in parallel, So

C12 = C1 + C2 = 5 + 5 = 10 uF

Now C12 & C3 are in series, So

Ceq = C12*C3/(C12 + C3) = 10*10/(10 + 10) = 5 uF

Ceq = 5 uF

Now

Qeq = Ceq*V

Qeq = 5*10 = 50 uC

Now remember in capacitors parallel combination voltage distribution in each part will be same and in series combination charge distribution in each capacitor will be same.

Qeq = Q12 = Q3 = 50 uC

V3 = Q3/C3 = 50/10 = 5 V

V12 = V - V3 = 10 - 5 = 5 V

V12 = V1 = V2

V1 = 5 V

V2 = 5 V

Q1 = C1*V1 = 5*5 = 25 uC

Q2 = C2*V2 = 5*5 = 25 uC

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