1. A wire 1 m long carries a current of 5 A. The wire is at right angles to a uniform magnetic field. The force on the wire is 0.2 N. What is the magnetic field strength?
2. Now in number one, the wire is directed at an angle of 30°. What is the magnetic field strength?
3. A 10 cm long wire is at right angles to a uniform magnetic field of 0.06 T. A 4 A current is in the wire. What magnetic force does it experience? What is the magnetic force if the wire was at an angle of 40° to the magnetic field?
4. A beam of electrons travels at 3,000,000 m/s through a 0.04 T field. What force does the beam experience?
5. A square coil with 100 loops and sides of 5 cm is positioned perpendicularly to a uniform 0.06 T magnetic field. It is quickly and uniformly pulled out of the magnetic field (moving perpendicular to the field) to a region where the magnetic field suddenly drops to zero. It takes 0.10 sec for the whole coil to reach the field-free region. Find the change in magnetic flux in the coil. Calculate the emf and current induced if its resistance is 100 ohms.
6. A 9.2 cm diameter loop of wire containing 10 turns is initially oriented perpendicular to a 1.5 T magnetic field. It is rotated so that its plane is parallel to the field in 0.20 sec. Find the change in magnetic flux in the coil. Calculate the emf and current induced if its resistance is 50 ohms.
7. A wire 2 m long moves perpendicularly through a 0.08 T field at a speed of 7 m/s. What emf is induced? Knowing Ohm’s law and that the wire has a resistance of 0.50 ohms, what current flows?
8. The direction of a 0.045 T field is 60° above the horizontal. A wire 2.5 m long moves horizontally through this field at 2.4 m/s. What is the vertical component of the magnetic field? What emf is induced in the wire?
9. An electron (mass = 9.11 x 10^-31kg) travels at 2 x 10⁷m/s in a circular path in a 0.010 T magnetic field. What is the radius of its path? What is its kinetic energy? Ans: 0.011 m; 1.82 x 10^-16J
10. A transformer has input voltage and current of 12 V and 3 A. It has an output current of 0.75 A. If there are 1200 turns on the secondary, how many turns are on the primary? What is the output voltage? Is this a step-up or step-down transformer?
11. A model electric train requires a low voltage to operate. If the primary coil of its transformer has 400 turns and the secondary has 20 turns, how many volts will power the train when connected to a 120 V house circuit? Is this a step-up or step-down transformer? What is the input current if the current in the train is 0.50 A?
12. A wire bearing an upward current of 6 A is 10 cm to the left of a wire bearing a downward current of 8 A. What is the magnitude and the direction of the net magnetic field at a point 6 cm to the left of the 8 A wire?
13. Repeat number 12, but now the currents are both acting downward. Find the magnitude and direction of the net magnetic field at a point 2 cm to the right of the 8 A wire.

Magnetism Notes

Magnetism Homework