Multiple Choice Questions 1. Which of the following diagrams best represents the magnetic field created by the

Question:

Multiple Choice Questions
1. Which of the following diagrams best represents the magnetic field created by the rail currents in the region between the rails?

2. For a given mass, if the current were decreased by a factor of 2, the new exit speed v would be equal to
A. 2vi
B. ˆš2vi
C. vi/ˆš2
D. vi/2
3. Lengthening the rails would increase the exit speed because of
A. An increased rail resistance.
B. A stronger magnetic field between the rails.
C. A larger force on the armature.
D. A longer distance over which the force is present.
4. What change made to the railgun would reduce power consumption without lowering the exit speeds?
A. Lowering the rail current
B. Lowering the rail resistivity
C. Lowering the rail cross-sectional area
D. Reducing the magnetic field strength
5. If a projectile with a mass of 0.10 kg accelerates from a resting position to a speed of 10.0 m/s in 2.0 s, what will be the average power supplied by the railgun to the projectile?
A. 0.5 W
B. 2.5 W
C. 5.0 W
D. 10.0 W
6. When delivering a constant amount of power, why does the power lost to heat decrease as the transmission-line voltage increases?
A. Increasing the voltage decreases the required current.
B. Increasing the voltage increases the required current.
C. Increasing the voltage decreases the required resistance.
D. Increasing the voltage increases the required resistance.
An electromagnetic railgun is a device that can fire projectiles using electromagnetic energy instead of chemical energy. A schematic of a typical railgun is shown here.

The operation of the railgun is simple. Current flows from the current source into the top rail through a movable, conducting armature into the bottom rail, then back to the current source. The current in the two rails produces a magnetic field directly proportional to the amount of current. This field produces a force on the charges moving through the movable armature. The force pushes the armature and the projectile along the rails.
The force is proportional to the square of the current running through the railgun. For a given current, the force and the magnetic field will be constant along the entire length of the railgun. The detectors placed outside the railgun give off a signal when the projectile passes them. This information can be used to determine the exit speed v i and kinetic energy of the projectile. The projectile mass, rail current, and exit speed for four different trials are listed in the table.