1. The inner and outer surfaces of a cell membrane carry a negative and positive charge, respectively. Because of these charges, a potential difference of about 0.067 V exists across the membrane. The thickness of the membrane is 8.2 x 10^-9 m. What is the magnitude of the electric field in the membrane?

2. An electron is released from rest at the negative plate of a parallel plate capacitor and accelerates to the positive plate (see the drawing). The plates are separated by a distance of 1.2 cm, and the electric field within the capacitor has a magnitude of 2.2 x 10⁶ V/m. What is the kinetic energy of the electron just as it reaches the positive plate?

3. Two charges A and B are fixed in place, at different distances from a certain spot. At this spot the potentials due to the two charges are equal. Charge A is 0.15 m from the spot, while charge B is 0.45 m from it. Find the ratio q_B/q_A of the charges.