 # PHYS112 WVU Capacitance and Circuits homework Anonymous
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The questions in this section are to be answered by circling the correct multiple-choice answer AND providing a short justification of your answer in the space after the problem..

Name: Lab Day/Time: Monday Homework 6 Capacitance Multiple Choice Problems The questions in this section are to be answered by circling the correct multiple-choice answer AND providing a short justification of your answer in the space after the problem.. Monday Homework Problem 6.1 Consider a capacitor with capacitance C charged with a battery so that one of the capacitor plates has a charge Q. After charging, the battery is disconnected. The capacitor has potential energy U . If the capacitance is increased to 2C while the charge on the plates is undisturbed, what is the new energy of the capacitor in terms of the original energy U ? Select One of the Following: (a) U (b) 2U (c) 4U (d) U/2 (e) U/4 Monday Homework Problem 6.2 A parallel-plate capacitor with plate area A and plate spacing d is charged to a potential difference ∆V by a connection to a battery. If the plate area is increased to 2A while the potential difference and the separation stay the same, what happens to the charge stored on one capacitor plate as the area is increased? Select One of the Following: (a) The charge increases. (b) The charge decreases. (c) The charge charge stays the same. Monday Homework Problem 6.3 You build a parallel plate capacitor with aluminum foil and plastic wrap (guess κ = 1.5 and thickness d = 0.05mm) as the dielectric. You charge the capacitor to 100V. How much plate area is required to store 50J of energy? Select One of the Following: (a) 7 × 107 m2 (b) 3 × 105 m2 (c) 4 × 104 m2 (d) 2 × 102 m2 (e) 3 × 10−2 m2 1 Monday Homework Problem 6.4 A positively charged particle is placed at the point A in the figure to the right. Select the direction the particle will move if released at point A. Equipotential lines are drawn and the potential of each is labelled. The potential changes smoothly between the equipotentials. 10V Select One of the Following: (a) +x̂ A (b) −x̂ 3V y (c) +ŷ (d) −ŷ (e) The charge will not move. 1V x (f) The direction of motion cannot be determined. Monday Homework Problem 6.5 The European High Magnetic Field Laboratory claims to have the world’s largest capacitor bank. The bank can hold 50MJ = 5.0 × 107 J of energy when charged to a voltage of 24, 000V. What is the capacitance of the capacitor bank? Select One of the Following: (a) 3.6 × 10−3 F (b) 0.088F (c) 0.17F (d) 23F (e) 4, 200F Monday Homework Problem 6.6 A 2µF parallel-plate capacitor with plate separation 2.0mm is connected to a 6V battery. What is the electric field between the plates when the system is in equilibrium? Select One of the Following: (a) 1 × 10−2 N C (b) 1 N C (c) 50N/C (d) 3000N/C (e) 6000N/C 2 Monday Homework Problem 6.7 To exploit the properties of different dielectric materials, a capacitor is made out of three layers of dielectric as shown to the right. The two outer layers have the same thickness, ℓ1 = 1.0 × 10−4 m. The central layer has thicknes ℓ2 = 5.0×10−5 m. The total area of one of the conducting plates which surround the dielectric is 3.0m2 . Each layer has a different dielectric constant κ1 = 3.2, κ2 = 9.0, and κ3 = 5.5. What is the capacitance, Cab of the system? Select One of the Following: a Conductor κ1 κ2 (a) 0.48µF κ3 (b) 1.6µF (c) 4.9µF Conductor b (d) 43µF (e) 310µF Monday Homework Problem 6.8 In a region of space, the electric potential is constant and positive. What can be inferred about the electric field in the region? Select One of the Following: (a) The electric field is zero. (b) The electric field is positive. (c) The electric field is negative. (d) Nothing can be inferred about the electric field. Monday Homework Problem 6.9 The electric field points to Select One of the Following: (a) lower (b) higher (c) equal (d) There is no relation between field direction and the change in potential. 3 electric potential. Monday Homework Problem 6.10 Select the inequality for the potential at the points A, B, C, and D based on the electric field map. A Select One of the Following: (a) VC > VB > VA > VD (b) VC = VD > VB > VA D (c) VB > VA > VD > VC (d) VD > VA > VB > VC B (e) VB > VC > VD > VA (f) VC > VB > VD > VA (g) VC = VD > VA = VB (h) VA = VB = VC = VD 4 C

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Running head: Monday homework on capacitance

Monday homework on a capacitance
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1

Monday homework on capacitance
Question 6.1
U =Q^2/2C =CV^2/2
Given that C= 2C and Q= 1
U =Q^2/2C = 1^2/2*2C = 1/4C
U =1/4
Energy in capacitance in terms of U = 4U
Answer = (c) =4C
Question 6.2

Q =∆Vԑ0.A/d
Given that ∆V =constant, d= constant, A= 2A and ԑ0 = constant
Since Q is directly proportional to A hence as the, A increase Q also increases given all other
values constant
Answer = (a) The charge increases.
Question 6.3
C =K ԑ0A/d
But C =2U/V^2
C =2U/V^2= Kԑ0*A/d

2

Monday homework on capacitance
2*100/50^2 = 1.5 *8.854*10^-12 *A/0.00005
2500 =1.3281*10^-11 * A/0.00005
2500*0.00005 = 1.3281*10^-11 A
4*10^6/1.3281*-11=3.0 *10^5
Answer = (b) 3 × 10^5m2
Question 6.4
The charge particles always move from a low to a higher potential position in a field; hence for
this case positive particles at point A will move towards a 10V point in the y-axis.
An...

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