Exam 20: Electric Fields and Forces

A small 0.050-kg insulating sphere carries a charge of -60 μC and is hanging by a vertical silk thread from a fixed point in the ceiling. An external uniform vertical electric field is now applied. If the applied electric field has a magnitude of 3000 N/C and is directed downward, what is the tension in the silk thread? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

Two tiny particles having charges of +7.00 μC and -9.00 μC are placed along the y-axis. The +7.00-µC particle is at y = 0.00 cm, and the other particle is at y = 40.00 cm. Where must a third charged particle be placed along the y-axis so that it does not experience any net electric force due to the other two particles?

Three equal positive point charges +q are placed at the corners of a square of side d as shown in the figure. Which one of the arrows shown represents the direction of the net electric field at the center of the square?

The figure shows electric field lines arising from two small charged particles P and Q. Consider the following two statements: (i)The charge on P is smaller than the charge on Q. (ii)The electrostatic force on P is smaller than the force on Q. Which of the above statements are true?

Four point charges Q of equal magnitude and sign are arranged on three of the corners of the square of side d as shown in the figure Which one of the arrows shown represents the net force acting on the charge at the upper right hand corner of the square?

A small charged plastic ball is vertically above another charged small ball in a frictionless test tube as shown in the figure. The balls are in equilibrium a distance d apart. If the charge on each ball is doubled, the equilibrium distance between the balls in the test tube would become

One point charge +Q is placed at the center of a square, and a second point charge -Q is placed at the upper-left corner of the square. It is observed that an electrostatic force of magnitude 2.0 N acts on the positive charge at the center. Now a third charge -Q is placed at the lower-left corner of the square, as shown in the figure. What is the magnitude of the net force that acts on the center charge now?

An electron is projected with an initial velocity v₀ = 8.4 × $10 ^ { 7 }$ m/s along the y-axis, which is the centerline between a pair of charged plates, as shown in the figure. The plates are 1.0 m long and are separated by 0.10 m. A uniform electric field of magnitude E in the +x-direction is present between the plates. If the magnitude of the acceleration of the electron is measured to be $8.9 \times 10 ^ { 15 } \mathrm {~m} / \mathrm { s } ^ { 2 }$ what is the magnitude of the electric field between the plates? (e = 1.6 × 10^-19 C, m_electron = 9.11 × 10^-31 kg)

As shown in the figure, three charges are at corners of a rectangle. The charge in the bottom right corner is Q = - 90 nC, and all the other quantities are accurate to two significant figures. What is the magnitude of the net electrical force on Q due to the other two charges? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

When 1.0-µC point charge is 15 m from a second point charge, the force each one experiences a force of 1.0 µN. What is the magnitude of the second charge? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

An electron and a proton are released simultaneously from rest and start moving toward each other due to their electrostatic attraction, with no other forces present. Which of the following statements are true just before they are about to collide? (There could be more than one correct choice.)

A negatively-charged rod is brought close to (but does not touch)two neutral spheres that are in contact with each other but insulated from the ground. If the two spheres are then separated, what kind of charge will be on the spheres?

A plastic rod is charged up by rubbing a wool cloth, and brought to an initially neutral metallic sphere that is insulated from ground. It is allowed to touch the sphere for a few seconds, and then is separated from the sphere by a small distance. After the rod is separated, the rod

A small object with a 5.0-μC charge is accelerating horizontally on a friction-free surface at 0.0050 m/s2 due only to an electric field. If the object has a mass of 2.0 g, what is the magnitude of the electric field?

As shown in the figure, three charges are at the vertices of an equilateral triangle. The charge Q is 6.7 nC, and all the other quantities are accurate to two significant figures. What is the magnitude of the net electric force on the charge Q due to the other two charges? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

An electron is placed in a uniform electric field of 4.5 × 104 N/C that points to the right. (e = 1.6 × 10^-19 C, m_electron = 9.11 × 10-31 kg) (a)What are the magnitude and direction of the force on the electron? (b)If the electron is released from rest, what is its speed after 3.0 ps?

A +5.0-μC point charge is placed at the 0 cm mark of a meter stick and a -4.0-μC charge is placed at the 50 cm mark. What is the net electric field at the 30 cm mark? (k = 1/4πε₀ = 8.99 × 10⁹ N ∙ m²/C²)

A small glass bead has been charged to 1.9 nC. What is the strength of the electric field 2.0 cm from the center of the bead? (k = 1/4πε₀ = 8.99 × 10⁹ N ∙ m²/C²)

The figure shows two tiny 5.0-g spheres suspended from very light 1.0-m-long threads. The spheres repel each other after each one is given the same positive charge and hang at rest when θ = 4.1°. What is the charge on each sphere? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

(a) (b) X and Y are two initially uncharged metal spheres on insulating stands, and they are in contact with each other. A positively charged rod R is brought close to X as shown in part (a)of the figure. Sphere Y is now moved away from X, as shown in part (b). What are the final charge states of X and Y?