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Grasp the wire with your right hand so that your thumb points in the direction of the current. Your fingers will wrap around the wire in the same sense as B |
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Let your thumb point in the direction of the first vector mentioned on the RHS. Let your index finger point in the direction of the second vector mentioned. The force will point in a direction perpendicular to the plane of v and B in the same sense as the middle finger of your right hand. |
Note that in most of these problems the wire is long and straight so that we can avoid end-of-wire anomalies
1. A wire carries a current of 8 A. Determine the magnitude of the B-field 5 cm, 10 cm & 15 cm away. Show the direction of these field vectors.
2. Two long straight parallel wires carry currents of 8 A and 10 A in the same direction. Points A, B, and C all lie in the same plane as the wires. Point A is outside the wires and 10 cm from the 8A wire. Point B is outside the wires and 10 cm from the 10 A. Point C is midway between the wires. The wires are 25 cm apart. Determine B net at points A, B, And C.
3. Repeat problem #2 except that the currents are oppositely directed.
4. Go back to #2 again. We place a third wire so that it is parallel to, and in the same plane as, the other two. This third wire is 25 cm above the 10 A wire.a) What should be the magnitude and direction of the current in the third wire in order to render B net = 0 at point A? b) Repeat question 4A) for points B an d C.
5. Consider long, straight, parallel wires arrayed at the corners of a square 20 cm on a side. Each carries a current of 5 A (three wires into the page; lower left wire out of page). Find B net at the center of the array.
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6. Consider an electron moving at 10 percent of the speed of light. (For nor, ignore relativistic effects.) Determine its kinetic energy. (You'll need to know the mass of the electron; see the number in the box above.) The answer you get for this problem is in Joules. The exponent of power of 10 would tell you that the joule is not an appropriate size unit for measuring such a small energy. A more convenient for energy is the electron-volt. See the box for this equivalent and give the kinetic energy of the electron in eV.
7. Consider two parallel plates each with a hole in the center. The plates are connected to it power source that applies a potential of 50,000 volts between the plates. The left plate is positive, the right plate is negative. Protons are injected into a small hole at the the left plate and accelerated across the gap through a hole in the right plate. What kinetic energy (in Joules and in eV.) do the protons acquire by being pushed between the plates? What velocity do they acquire from the trip? The protons now pass through the hole in the right plate and enter a region of uniform magnetic fields of 5 T pointing into the page What is the radius of the path of the protons as they move through the magnetic field?
.8. A proton, a deuteron, and an alpha particle are all given the same kinetic energy. Compare their velocities. ( answer in terms of KE and m ).
9. . A proton, a deuteron, and an alpha particle are accelerated through the same potential. Compare their KEs.. Compare their velocities. Answer in terms of KE, V,q, m
10. A long straight wire carries a current 10 A. Point P is 10 centimeters from the wire is located above the wire. A proton moving at 1 x 20^6 m/s is about the pass-through point P. What force does the field around the wire exert on a proton at P. if a proton passes parallel to the wire in the same directions to current; B.) proton passes parallel to the wire in the opposite direction to current; C.) at right angles to the direction in part A.
11. An electron is accelerated through
a potential of 350 V, then enters a magnetic field where
B = 2 T. Describe the path of the electron.
12.Consider two long straight parallel wires carrying currents of 6 A (top wire, call it X) and 10 A (bottom wire, call it Y) in the same direction. The wires are .25 m apart. Determine the force per unit length for each wire. (When the length of the wire is not given, you cannot solve for the force on the entire wire; F/l is he best you can do.
13. Repeat problem 12, this time with the currents oppositely directed.
14. Revisit problem 12, this time add a third wire (call it Z), parallel to the other two and in the same plane, wire Z placed 20 cm from wire Y. What should be the magnitude and direction of the current in wire Z that will render Fnet on wire Y = 0? (NOTE: there are two avenues of approach for this problem. 1) set up the current in wire Z so that FZY = IlY x BZ opposes FXY; or 2) set up the current in wire Z so that in the location of wire Y, BX and BZ cancel. Either approach should yield the same answer.)
15. Four wires are placed at the corners of a square that is a distance a on a side. The wires each carry the same current I in the same direction. Find FNET/ /L on the upper left wire.
16. A metal bar of length L and mass M is suspended from two vertical wires each 1 m long. A second similar bar suspended in the same way is brought alongside the first. Each bar is supplied with a current causing the bars to spread apart so that the angle between them is 20 degrees. Find the magnitude and direction of current in each bar that will cause this to happen.
Last edited 03/11/09