Exam 20: Electric Fields and Forces

A pair of charged conducting plates produces a uniform field of 12,000 N/C, directed to the right, between the plates. The separation of the plates is 40 mm. An electron is projected from plate A, directly toward plate B, with an initial speed of v₀ = 2.0 × 10⁷ m/s. What is the speed of the electron as it strikes plate B? (e = 1.6 × 10^-19 C, m_electron = 9.11 × 10^-31 kg)

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?

Two equal and opposite charges are a small distance apart, forming an electric dipole. A positive charge +q is placed above these charges, as shown in the figure, equidistant from both of them. Which diagram below best gives the direction of the net force the dipole exerts on the charge +q?

Two 10¢ coins (dimes) carrying identical charges are lying 2.5 m apart on a table. If each of these coins experiences an electrostatic force of magnitude 2.0 N due to the other coin, how large is the charge on each coin? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

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?

A proton is located at the point (x = 1.0 nm, y = 0.0 nm) and an electron is located at the point $( x = 0.0 \mathrm {~nm}$ $y = 4.0 \mathrm {~nm} )$ Find the magnitude of the electrostatic force that each one exerts on the other. (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C², e = 1.6 × 10^-19 C)

The force of attraction that a -40.0 μC point charge exerts on a +108 μC point charge has magnitude 4.00 N. How far apart are these two charges? (k = 1/4πε₀ = 8.99 × 10⁹ N ∙ m²/C²)

A piece of plastic has a net charge of +2.00 μC. How many more protons than electrons does this piece of plastic have? (e = 1.60 × 10^-19

Two parallel square metal plates that are 1.5 cm apart and 22 cm on each side carry equal but opposite charges uniformly spread out over their facing surfaces. How many excess electrons are on the negative surface if the electric field between the plates has a magnitude of 18,000 N/C? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C², e = 1.6 × 10^-19 C)

A solid aluminum cube rests on a wooden table in a region where a uniform external electric field is directed straight upward. What can we say concerning the charge on the top surface of the cube?

Electrically neutral objects cannot exert an electrical force on each other, but they can exert a gravitational force on each other.

If two objects are electrically attracted to each other,

Three equal-magnitude point charges of varying signs 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?

A small styrofoam ball of mass 0.120 g is placed in an electric field of 6000 N/C pointing downward. What excess charge must be placed on the ball for it to remain suspended in the field?

Consider a container of 2.0 g of hydrogen, H2 (one mole). Suppose you removed all the electrons and moved them to the other side of the earth (Earth's radius is 6380 km, k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C², N_A = 6.022 × 10²³ molecules/mol, e = 1.60 × 10^-19 C) (a) How much charge is left behind after you remove the electrons? (b) What electric force do the protons exert on the electrons after they are separated as described?

Two small identically charged balls are a certain distance apart. The vectors in the figure show the magnitude and direction of the electrostatic force on each ball due to the other one. Suppose that the charge on the left ball is now doubled (represented by two plus signs). Which vector diagram below best represents the forces that now act on each of the two balls?

Two point charges, Q₁ and Q₂, are separated by a distance R. If the magnitudes of both charges are doubled and their separation is also doubled, what happens to the electrical force that each charge exerts on the other one?

The figure shows two unequal charges, +q and -Q. Charge -Q has greater magnitude than charge +q. Point X is midway between the charges. In what section of the line will there be a point where the resultant electric field is zero?

The three point charges +4.0 μC, -5.0 μC, and -9.0 μC are placed on the x-axis at the points x = 0 cm, x = 40 cm, and x = 120 cm, respectively. What is the x component of the electrostatic force on the -9.0 μC charge due to the other two charges? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

A particle of charge +2q is placed at the origin and particle of charge -q is placed on the x-axis at x = 2a. Where on the x-axis can a third positive charge be placed so that the net electric force on it is zero?