Download lab9 - phys2lab

Introduction:
In unit 9 lab we will learn how to calculate the earth’s magnetic field by measuring the
magnetic field generated by running a current through a galvanometer, and measuring the
difference in angles between a set north point due to earth’s magnetic field and the north point
of the magnetic field generated when the galvanometer is turned on. We will use the right
hand rule to show that this magnetic field is perpendicular to the plane of the loop of the
galvanometer. The equipment used included a tangent galvanometer, a lab-volt power supply,
and a 10ohm resistor.
Procedure:
In this experiment we utilized a Tangent Galvanometer to ascertain the magnetic field of
the Earth in Orlando, Florida. Generally magnetic fields are generated anytime there is a flow of
electric current. If a current flows through a circular loop of a radius R, a magnetic field is
generated at the center of the loop. Using the right-hand rule, the field is perpendicular to the
plane of the loop. The magnitude can be determined by using the equation:
B = µ0 N I / 2R
N being the number of turns in the coil, I the current flowing through the coil, and µ0 being the
preset constant that equals 4π x 10-7 T∙m/A. and is the permeability of free space.
In the experiment, the tangent galvanometer was composed of a circular coil and in the middle
of the galvanometer was a compass used to find the direction of the magnetic field at the
center. With no current, the galvanometer was moved so that it ran parallel to Earth’s magnetic
field. Then it was connected to a resistor and a power supply. A number of turns would be
determined, such as 15, and the current flowing through would be altered to witness the
change in the needle of the compass. With this we would record a series of measurements of
the angle α which the compass makes with the plane of the coil as a function of current. Three
separate series would be record, current and α at 15 turns, 10 turns, and 5 turns. With these
numbers we could make three graphs of current (I) vs. tanα and realize that they would plot a
fairly straight line. To determine the slopes of each graph we would use linear regression. From
these slopes we could calculate the Earth’s magnetic field at the point on Earth we are
measuring, this magnetic field being titled Be. This is determined using the equation above
altered to look like:
Be = µ0 N I / 2R
The radius was measured separately and recorded as 0.095 m.
Data Analysis:
See tables and chart attached.
Conclusion:
In conclusion, the mean value we measured for the Earth’s magnetic field in Orlando,
Florida is 2.47 x 10^ -5 Tesla. According to www.coolmagnetman.com, Earth’s magnetic field is
5.0 x 10^-5 T. The difference in our measurements vs. the online source’s could come from the
location that the magnetic field was measured for the website and also because it was difficult
for us to measure an exact angle that the compass made. Regardless, we feel the experiment
was quite successful as we managed to collect relatively consistent data and learned how to
use the tangent galvanometer.