Electric Field Practice Problems

Two tiny balls charged to +5.1 μC and +7.21 μC are used for an electrostatics experiment.  They are joined together using a massless non-conducting rod 3.21 cm long. The +5.1 μC charged ball is fixed in place while the other charged ball is free. The assembly lies in a region of an even electric field with a magnitude of 2.0 × 10⁸ N/C.  Determine the tension/compression in the connecting rod. Model the balls as point charges.

Two tiny charged spheres (may be modeled as point charges) are connected using a massless non-conducting rod of length 3.21 cm. One sphere has a charge of -5.1 μC whereas the other has a charge of +7.21μC. The sphere of charge -5.1μC has a fixed position while the other is free. The assembly is placed in an even external electric field of magnitude 2.0 × 10⁸ N/C. What is the tension in the rod?

Two small spheres separated by a distance 2d lie on the x-axis. Each sphere carries a positive charge q. The origin of the x-axis lies at the midpoint of the two charges. What is the electric field magnitude and direction at the origin? Treat the spheres like point charges.

An electron moves horizontally eastward at 7.20 × 10⁶ m/s. Determine the least electric field strength and direction of an electric field that slows the electron at a constant rate to a complete stop within 3.6 cm.

An electron moves horizontally to the east with a velocity of 2.40 × 10⁶ m/s. The electron enters an electric field that slows it uniformly. It comes to rest after covering 2.5 cm in the electric field. Determine the time taken by the electron to stop from the moment it enters the electric field.

A hydrogen ion (essentially a proton) has a horizontal velocity of 2.40 × 10⁶ m/s to the east. If the ion should stop within 4.0 cm inside an electric field, determine the minimum electric field strength and direction of an electric field that slows the ion uniformly.

An extremely long linear bar is charged by friction to 1.60 nC/m. The electric field has a magnitude of 6.40 N/C at a point R measured from the bar. Determine the value of R.

In a photoelectric experiment, 240 nm light is directed toward an aluminum cathode. Calculate the stopping voltage for the photoelectrons. The work function of aluminum is 4.28 eV.

The assembly of two charges below contribute to the electric field at point p in the image. Calculate the electric field at point p, giving the result using components. 

Four tiny spheres are charged to a charge q. They are assembled to form a square of length d. Half of the spheres are positively charged while the other half is negatively charged. Find the magnitude (in terms of q and d) and direction of the electric field created by the four spheres at the center of the square. Assume tiny balls behave like point charges.