Download Magnetic Fields, Forces, and EM Induction

Magnetic Fields, Forces, and EM Induction
Magnetic Fields & Forces
1. A wire 1.50 m long carrying a current of 10.0 A is at right angles to a uniform magnetic field.
The force acting on the wire is 0.60 N. What is the strength of the magnetic field?
2. The current is coming straight out of the page in Figure 1. Sketch the magnetic field the current
generates.
.
Figure 1
3. Figure 2 shows the end view of an electromagnet with the current as shown.
a. What is the direction of the magnetic field inside the loop?
b. What is the direction of the magnetic field outside the loop?
I
Figure 2
4. A wire 0.50 m long carrying a current of 8.0 A is at right angles to a uniform
magnetic field. The force on the wire is 0.40 N. What is the strength of the magnetic field?
5. A wire 25 cm long is at right angles to a 0.30-T uniform magnetic field. The current through the
wire is 6.0 A. What is the magnitude of the force on the wire?
6. A wire 625 m long is in a 0.40-T magnetic field. A 1.8-N force acts on the wire. What current
is in the wire?
7. A power line carries a 225-A current from east to west parallel to the surface of Earth.
a. What is the magnitude of the force acting on each meter of the wire due to Earth’s magnetic
field?
b. What is the direction of the force?
c. In your judgement, would this force be important in designing towers to hold these power
lines?
8. A wire carrying 15 A of current has a length of 25 cm between a magnetic field of 0.85 T. The
force on a current carrying wire in a uniform magnetic field can be found by F=BILsin. Find
the force on the wire if it makes an angle with the magnetic field lines of
a. 90.
b. 45.
c. 0.
9. A galvanometer deflects full scale for a 50.0 A current.
a. What must be the total resistance of the series resistor and the galvanometer to make a
voltmeter with 10.0 V full-scale deflection?
b. If the galvanometer has a resistance of 1.0 k, what should be the resistance of the series
(multiplier) resistor?
10. A beam of electrons moves at right angles to a 6.0 x 10-2 T magnetic field. The electrons have a
velocity of 2.5 x 106 m/s. What is the magnitude of the force on each electron?
11. A magnetic field of 16 T acts in a direction due west. An electron is traveling due south at 8.1 x
105 m/s. What is the magnitude and direction of the force acting on the electron?
12. A singly –ionized particle experiences a force of 4.1 x 10-13 N when it travels at right angles
through a 0.61 T magnetic field. What is the velocity of the particle?
Induced EMF and Currents
1. A wire segment, 31 m long, moves straight up through a 4.0 x 10-2 T magnetic field at a speed
of 15 m/s. What EMF is induced in the wire?
2. A wire, 20.0 m long, moves at 4.0 m/s perpendicularly through a 0.50 T magnetic field. What
EMF is induced in the wire?
3. An airplane traveling at 950 km/h passes over a region where Earth’s magnetic field is
4.5 x 10-5 T and is nearly vertical. What voltage is induced between the plane’s wing tips,
which are 75 m apart?
4. A straight wire, 0.75 m long, moves upward through a horizontal 0.30 T magnetic field at a
speed of 16 m/s.
a. What EMF is induced in the wire?
b. The wire is a part of a circuit with a total resistance of 11 . What current flows in the
circuit?
5. An EMF of 0.0020 V is induced in a 10-cm wire when it is moving perpendicularly across a
uniform magnetic field at a speed of 4.0 m/s. What is the size of the magnetic field?
Alternating Currents & Transformers
1. An electric stove is connected to an AC source with effective voltage of 240 V.
a. Find the maximum voltage across one of the stove’s elements when it is operating?
b. The resistance of the operating element is 11 . What effective current flows through it?
2. A step-up transformer has 80 turns on its primary. It has 1200 turns on its secondary. The
primary is supplied with an alternating current at 120 V.
a. What voltage is across the secondary?
b. The current in the secondary is 2.0 A What current flows in the primary circuit?
c. What is the power input and output of the transformer?
3. In a hydroelectric plant, electricity is generated at 1200 V. It is transmitted at 240,000 V.
a. What is the ratio of the turns on the primary to the turns on the secondary of a transformer
connected to one of the generators?
b. One of the plant generators can deliver 40.0 A to the primary of its transformer. What
current is flowing in the secondary?
4. A step-up transformer is connected to a generator that is delivering 125 V and 95 A. The ratio
of the turns on the secondary to the turns on the primary is 1000 to 1.
a. What voltage is across the secondary?
b. What current flows in the secondary?
5. The secondary of a step-down transformer has 50 turns. The primary has 1500 turns.
a. The EMF of the primary is 3600 V. What is the EMF of the secondary?
b. The current in the primary is 3.0 A. What current flows in the secondary?
6. The primary of a transformer has 150 turns. It is connected to a 120 V source. Calculate the
number of turns on the secondary needed to supply the following.
a. 600 V
b. 30.0 V
c. 6.0 V