1. Suppose all the electrons could be removed from earth.

(a) Find the force on a proton just above the Earth's surface under these conditions.

(b) Compare your answer in part (a) with the weight of the proton.

2. Four point charges are placed on the corners of a square of side d as shown in picture.

(a) Find the net force (magnitude and direction) of each charge.

3. Three capacitors are in series: C1= 45 µF, C2=65 µF and C3=80 µF.

(a) Compute the equivalence capacitance. The series combination is connected across a 48-V battery.

(b) Find the charge of each capacitor.

(c) Compute the energy stored in each capacitor.

(d) Show that the total energy you found in part (c) is the same as would be stored in a single capacitor with the equivalent capacitance you found in part (a).

4. Defibrillator: energy and power. A defibrillator uses a 225-µF capacitor charged to 2400 V.

(a) how much energy is stored in the capacitor.

(b) What is the power delivered to the patient if the capacitor discharged completely in 2.5ms?

5. Ion channel. The potential differences across the ion channel described in example 17.1 is 80 mV.

(a) What is the resistance of the Ion channel?

(b). The Ion channel can be modeled as a cylinder with a length of 6.0 nm and a diameter of 0.35 nm. What is the resistivity of the fluid filling the channel?

(c) At what rate is energy dissipated while the ions are flowing?

6. Two long parallel wires each carry 2.5 A in the same direction, with their center 1.5 cm apart.

(a) Find the magnetic field halfway between the wires.

(b) Find the magnetic field at a point in the same plane as the wires, 1.5 cm from one and 3.0 cm from the other.

(c) Find the force of interaction between the wires, and tell whether it is attractive or repulsive.

7. Four long parallel wires pass through the corners of a square 2.0 cm on a side. The wires each carry 2.5 A in the same direction.

(a) What is the magnetic field at the center of the square?

(b) What is the force per unit length on each wire?