1. A spark can jump between two nontouching conductors if the potential difference between them is sufficiently large. A potential difference of approximately 940 V is required to produce a spark in an air gap of 1.0 x 10^-4m. Suppose the light bulb in figure 22.4b is replaced by such a gap. How fast would a 1.3-m rod have to be moving in a magnetic field of 4.8 T to cause a spark to jump across the gap?

2. Near San Francisco, where the vertically downward component of the earth's magnetic field is 4.8 x 1.0^-5 T, a car is traveling forward at 25 m/s. An emf of 2.4 x 10^-3 V is induced between the sides of the car. A) Which side of the car is positive, the driver's side or the passenger's side? B) What is the width of the car?

3. A standard door into a house rotates about a vertical axis through one side, as defined by the door's hinges. A uniform magnetic field is parallel to the ground and perpendicular to this axis. Through what angle must the door rotate so that the magnetic flux that passes through it decreases from its maximum value to one-third of its maximum value?

4. A house has a floor area of 112 m^2 and an outside wall that has an area of 28 m^2. The earth's magnetic field here has a horizontal component of 2.6 x 10^-5 T that points due north at a vertical component of 4.2 x 10^-5 T that points straight down, toward the earth. Determine the magnetic flux through the wall if the wall faces (a) north and (b) east. C) Calculate the magnetic flux that passes through the door.