13 A charge of 4nC is placed in a uniform electric field that is directed vertically upward and has a magnitude of 3 × 104 ✓. What work is done by the electric force when the charge moves: a. 0.5 m to the right? b. 0.75 m straight up? m c. 1.0 meter at an angle of 30° to the horizontal (upward and to the right)?

(a) How much charge can be placed 011 a capacitor with air between the plates before it breaks down if the area of each plate is 5.00 cm2? (b) What If? Find the maximum charge if polystyrene is used between the plates instead of air.

Two 5.00-nC charged particles are in a uniform electric field with a magnitude of 625 N/C. Each of the particles is moved from point A to point B along two different paths, labeled in Figure P26.65. a. Given the dimensions in the figure, what is the change in the electric potential experienced by the particle that is moved along path 1 (black)? b. What is the change in the electric potential experienced by the particle that is moved along path 2 (red)? c. Is there a path between the points A and B for which the change in the electric potential is different from your answers to parts (a) and (b)? Explain. FIGURE P26.65 Problems 65, 66, and 67.

A 5.00-nC charged particle is at point B in a uniform electric field with a magnitude of 625 N/C (Fig. P26.65). What is the change in electric potential experienced by the charge if it is moved from B to A along a. path 1 and b. path 2?

At a certain distance from a charged particle, the magnitude of the electric field is 500 V/m and the electric potential is 3.00 kV. (a) What is the distance to the particle? (b) What is the magnitude of the charge?

A parallel-plate capacitor has charge of magnitude 9.00F on each plate and capacitance 3.00F when there is air between the plates. The plates are separated by 2.00 mm. With the charge on the plates kept constant, a dielectric with =5 . is inserted between the plates, completely filling the volume between the plates, (a) What is the potential difference between the plates of the capacitor, before and after the dielectric has been inserted? (b) What is the electrical field at the point midway between the plates before and after the dielectric is inserted?

(a) Find the electric potential difference Ve required to stop an electron (called a stopping potential) moving with an initial speed of 2.85 107 m/s. (b) Would a proton traveling at the same speed require a greater or lesser magnitude of electric potential difference? Explain. (c) Find a symbolic expression for the ratio of the proton stopping potential and the electron stopping potential. Vp/Ve.

(a) What is the direction and magnitude of an electric field that supports the weight of a free electron near the surface of Earth? (b) Discuss what the small value for this field implies regarding the relative strength of the gravitational and electrostatic forces.

Problems 72, 73, and 74 are grouped. 72. A Figure P26.72 shows a source consisting of two identical parallel disks of radius R. The x axis runs through the center of each disk. Each disk carries an excess charge uniformly distributed on its surface. The disk on the left has a total positive charge Q, and the disk on the right has a total negative charge Q. The distance between the disks is 3R, and point A is 2R from the positively charged disk. Find an expression for the electric potential at point A between the disks on the x axis. Approximate any square roots to three significant figures. FIGURE P26.72 Problems 72, 73, and 74.

(a) What magnitude point charge creates a 10,000 N/C electric field at a distance of 0.250 m? (b) How large is the field at 10.0 m?