Static Electricity

558 46) A force of 2.4*10^2 exists between a positive charge of 8*10^-5 C and a positive charge of 3*10^-5. What distance separates the charges?

((9*10^9)((8*10^-5)(3*10^-5))/2.4*10^2 =0.3 m

558 45) A positive and negative charge each of magnitude of 2.5*10^-5 C, are separated by a distance of 15 cm. Find the force on each of the particles.

((9*10^9)(2.5*10^-5)(2.5*10^-5))/(1.5*10^-1) =2.5*10^2 N, toward the other charge

552 13)----------Sphere A is located at the origin and has a charge of +2x10-6 C. Sphere B is located at +0.60 m on the x axis and has a charge of -3.6x10-6. Sphere C is located at +0.80 m n the x axis and has a charge of +4x10-6 C. Determine the net force on sphere A?

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558 43) A strong lightning bolt transfers about 25 C to Earth. How many electrons are transferred?

-25*(1/-1.6*10^-19) or 1.6*10^20 electrons

553 16) When electroscope is charged, the leaves rise to a certain angle and remain at that angle. Why do they not rise farther?

As the leaves move farther apart, the electric force between them decreases until it's balanced by the gravitational force pulling down on the leaves

545 3) A pith ball is a small sphere made of a light material, such as plastic foam, often coated with a layer of graphite or aluminum paint. How could you determine whether a pith ball that is suspended from an insulating thread is neutral, is charged positively, or is charged negatively?

Bring a negative charge rod near the ball and if it attracts its of opp charge (pos) or neutral. To find out which bring a positively charged object if they repel its positive, if it attracts its neutral

545 7) You can charge a rubber rod negatively by rubbing it with wool. What happens when you rub a copper rod with wool?

Copper is conductor, it remains neutral as long as its in contact with your hand.

566 7) What is the magnitude of the electric field strength at a distance twice as far from the point charge in (4*10^-6)

E=(K)q/d^2 (9*10^9) (4*10^-6)/1.2^2 =2.6*10^4....

566 8) What is the electric field at a position that is 1.6 m east of a point charge of 7.2*10^-6 C?

E=(K)q/d^2 or (9*10^9) (7.2*10^-6)/1.6^2 =2.5*10^4

565 2) A negative charge of 2*10^-8 C experiences a force of 0.060 N to the right in an electric field. What are the field's magnitude and direction at that location?

E=f/q or 0.060/2*10^-8 3*10^6, directed to the left

565 1) A positive test charge of 5*10^-6 C is in an electric field that exerts a force of 2*10^-4 N on it. What is the magnitude of the electric field at the location of the test charge?

E=f/q or 2*10^-4/5*10^-6 =4*10^1

565 3) A positive charge o 3*10^-7 C is located in a field of 27 N/C directed toward the south. What is the force acting on that charge?

E=f/q or F=eq 27*3*10^-7 8.1*10^-6 N South

566 9) The electric field that is 0.25 m from a small sphere is 450 N/C toward the sphere. What is the charge on the sphere?

E=f/q=(K)q/d^2 or q=Ed^2/k 450*0.25^2/ 9*10^9 -3.1*10^-9 towards it

566 6) What is the magnitude of the electric field strength at a position that is 1.2 m from a point charge of 2.4*10^-6 C?

E=kq/r^2 or ((9*19^9)*(2.4*10^-6))/1.2^2 4840315.47

552 10) A negative charge of 2.0x10-4 C and a positive charge of 8.0x10-4 C are seperated by 0.3 m. What is the force between the two charges?

F=kq(q2)/r^2 or (9*10^9)*(2*10^-4)*(8*10^-4) / 0.3^2 =1.6*10^4

552 12) A negative charge of -6x10-6 C exerts an attractive force of 65 N on a second charge that is 0.050 m away. What is the magnitude of the second charge?

Fd/kq or (65*0.050) / ((9*10^9)*(-6*10^-6))= 3*10^6

553 15) How are electric force and distance related? How would force change if the distance between two charges were tripled?

Force and distance are inversely related. The force exerted on each other becomes 1/9

558 24) List some insulators and conductors?

Insulators- dry air, wood, plastic, glass, cloth; Conductors- metals, tap water, and your body

558 36) In what ways are electric and gravitational forces similar? How are they different?

Inverse square dependence on distance, force proportional to product of two masses or charges; different:only one sign of mass, so gravitational force is always attractive; two signs of charge, so electric force is attractive or repulsive

545 4) A rubber rod can be charged negatively when it is rubbed with wool. What happens to the charge of the wool? Why?

It becomes positive, it gives up electrons to the rod.

558 25) What property makes metal a good conductor and rubber a good insulator?

Metals contain free electrons, Rubber contains bound electrons

545 5) An apple contains trillions of charged particles. Why don't two apples repel each other when they are brought together?

Neutral to each other

558 23) If you comb your hair on a dry day, the comb can becomes positively charged. Can your hair remain neutral? Explain?

No, by conservation of charge your hair becomes negatively charged

558 27) If you wipe a compact disc with a clean cloth, why does the CD then attract dust?

Rubbing the CD charges it. Neutral particles such as dust are attracted to a charged object.

558 34) Lightening usually occurs when a negative charge in a cloud is transported to Earth. If Earth is neutral, what provides the attractive force that pulls the electrons toward Earth?

The charge in the clouds repels neutrons on Earth, causing a charge separation by induction. The side of Earth closest to the cloud is positive, resulting in an attractive force.

545 1) After a comb is rubbed on a wool sweater, it is able to pick up small pieces of paper. Why does the comb lose that ability after a few minutes?

The comb loses its charge to its surroundings and becomes neutral once again

558 37) The constant K in Coulomb's equation is much larger than constant G in the universal gravitation equation. Of what significance is this?

The electric force is much larger than the gravitational equation

545 6) Suppose you hang a long metal rod from silk threads so that the rod is isolated. You then touch a charged glass rod to one end of the metal rod. Describe the charges on the metal rod?

The glass rod attracts electrons off the metal rod and becomes positively charged. The charge is distributed uniformly along the rod.

558 33) A charged rod is brought near a pile of tiny plastic spheres. Some of the spheres are attracted to the rod, but as soon as they touch the rod, they are flung off in different directions.

The natural spheres are initially attracted to the charged rod, but they acquire the same charge as the rod when they touch it. As a result are repelled from the rod.

558 26) Why do socks taken from a clothes dryer sometimes cling to other clothes?

They have been charged by contact, and thus, are attracted to clothing that is neutral or has an opposite charge

558 32) Using a charged rod and an electroscope, how can you find whether or not an object is a conductor?

Use an insulator to hold one end of the object against the electroscope. Touch the other end with the charged rod. If the electroscope indicates a charge, the object is a conductor.

566 10) How far from a point charge of 2.4*10^-6 must a test charge be placed to measure a field of 260 N/C?

d=square root Kq/e (9*10^9) * (2.4*10^-6)/ 260 =7.7

558 44) Two electrons in an atom are separated by 1.6*10^-19, 10 m, the typical size of an atom. What is the electric force between them?

k(q1)(q2)/d^2 ((9*10^9)(1.6*10^-19)(1.6*10^-19))/ 1*10^-8 N, away from each other --

558 49) The spheres are 16 cm apart, and the force between them is 0.28 N. What are the charges on the two spheres?

square root Fd^2/3K (0.28)(0.16)^2/3(9(10^9) or 5.2*10^-7 =qa 3qa= 1.5*10^-7= qb