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Electrostatic Charges & Fields

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Problem 13 :-
In figure 21-26 in attached file 3 particle 1 of charge +1.0 uC and particle 2 of charge
-3.0 uC are held at separation L = 10.0cm on an x axis.
If particle 3 of unknown charge (q3) is to be located such that the net electrostatic force on it from particles1 and 2 is zero.
What must be the (a)x axis and (b) y axis co-ordinates of particle3??

Problem 8.
In figure 22-30 in attached file 4 particle 1 of charge q1= -5.00q and particle 2 of charge +2.00q are fixed to an x axis.
(a) As a multiple of distance L, at what coordinate on the axis is the net electric field of the particles zero?
(b) Sketch the electric field lines.

Problem 26.
Charge is uniformly distributed around a ring of radius R= 2.40cm and the resulting electric field magnitude E is measured along the ring's central axis (perpendicular to the plane of the ring).

At what distance from the ring's center is E maximum?

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Physics/ answers to questions

1. Which one of the following statements best explains why it is possible to define an electrostatic potential in a region of space that contains an electrostatic field?

a. Work must be done to bring two positive charges closer together
b. Like charges repel one another and unlike charges attract one another
c. A positive charge will gain kinetic energy as it approaches a negative charge
d. The work required to bring two charges together is independent of the path taken
e. A negative charge will gain kinetic energy as it moves away from another negative charge

2. Two positive point charges are separated by a distance R. If the distance between the charges is reduced to R/2, what happens to the total electric potential energy of the system?

a. It is doubled.
b. It remains the same.
c. It increases by a factor of 4.
d. It is reduced to one-half of its original value
e. It is reduced to one-fourth of its original value

3. Two point charges are arranged along the x axis as shown the figure. At which of the following values of x is the electric potential equal to zero? Note: At infinity, the electric potential is zero.

a. +0.05 m
b. +0.29 m
c. +0.40 m
d. +0.54 m
e. +0.71 m

4. If the work required to move a +0.35 C charge from point A to point B is +125 J, what is the potential difference between the two points?

a. Zero volts
b. 44 V
c. 88 V
d. 180 V
e. 360 V

5. A charge is located at the center of sphere A (radius RA = 0.0010 m), which is in the center of sphere B (radius RB = 0.0012 m). Spheres A and B are both equipotential surfaces. What is the ratio VA/VB for the potentials of these surfaces?

a. 0.42
b. 0.83
c. 1.2
d. 1.4
e. 2.4

6. A parallel plate capacitor has a potential difference between its plates of 1.2 V and a plate separation distance of 2.0 mm. What is the magnitude of the electric field if a material that has a dielectric constant of 3.3 is inserted between the plates?

a. 75 V/m
b. 180 V/m
c. 250 V/m
d. 400 V/m
e. 500 V/m

Test 2
7. How many electrons flow through a battery that delivers a current of 3.0 A for 12 s?

a. 4
b. 36
c. 4.8 × 1015
d. 6.4 × 1018
e. 2.2 × 1020

8. Which one of the following statements concerning superconductors is false?

a. Below is critical temperature, the resistivity of a superconductor is zero Ω-m.
b. Critical temperatures for some superconductors exceed 100 K.
c. All materials are superconducting at temperatures near absolute zero kelvin
d. A constant current can be maintained in a superconducting ring for several years without an emf.
e. Superconductors are perfect conductors

9. When a 1500-W hair dryer is in use, the current passing through the dryer may be represented as I = (17.7 A) sin (120πt). What is the rms current for this circuit?

a. 17.7 A
b. 12.5 A
c. 85.7 A
d. 25.0 A
e. 8.85 A

10. Some light bulbs are connected in parallel to a 120 V source as shown in the figure. Each bulb dissipates an average power of 60 W. The circuit has a fuse F that burns out when the current in the circuit exceeds 9 A. Determine the largest number of bulbs, which can be used in this circuit without burning out the fuse.

a. 9
b. 17
c. 25
d. 34
e. 36

11. A non-ideal battery has a 6.0-V emf and an internal resistance of 0.6Ω. Determine the terminal voltage when the current drawn from the battery is 1.0 A.

a. 5.0 V
b. 6.0 V
c. 5.4 V
d. 6.66 V
e. 5.8 V

12. Three parallel plate capacitors, each having a capacitance of 1.0 μF are connected in parallel. The potential difference across the combination is 100 V. What is the charge on any one of the capacitors?

a. 30 μC
b. 100 μC
c. 300 μC

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