Question

describe procedure to determine the strength of the Earth's magnetic field using helmholtz coils and a compass

Answer 1

This lab consists of three main parts. In each you will measure the magnetic field
generated either by bar magnets or by current carrying coils.
Part 1: Mapping Magnetic Field Lines Using Mini-Compasses
Using a compass you will follow a series of field lines originating near the north pole of a
bar magnet.
Part 2: Constructing a Magnetic Field Diagram
A pair of bar magnets are placed so that either their opposite poles or same poles are
facing each other and you will map out the field lines from these configurations.
Part 3: Helmholtz Coil
In this part you will use the magnetic field sensor to measure the amplitude of the
magnetic field generated from three different geometries of current carrying wire loops

Part 1: Mapping Magnetic Field Lines Using Mini-Compasses

1. Tape a piece of brown paper (provided) onto your table.

2. Place a bar magnet about 3 inches from the far side of the paper, as shown below.

Trace the outline of the magnet on the paper.

3. Place a compass near one end of the magnet. Make two dots on the paper, one at

the end of the compass needle next to the magnet and the second at the other end

of the compass needle. Now move the compass so that the end of the needle that

was next to the magnet is directly over the second dot, and make a new dot at the

other end of the needle. Continue this process until the compass comes back to

the magnet or leaves the edge of the paper. Draw a line through the dots and

indicate with an arrowhead the direction in which the North end of the needle

pointed, as shown below

4. Repeat the process described above several more times (~4 field lines), starting at

different locations on the magnet. Work fairly quickly – it is more important to

get a feeling for the shape of the field lines than to map them precisely

Part 3: Helmholtz Coil

In this part we are going to measure the z-component of the field along the z-axis (central

axis of the coils)

3A: Using a Single Coil

1. With the power supply off, connect the red lead from the power supply to the red

plug of the top coil, and the black lead to the black plug of the top coil. Turn the

current knob fully counter-clockwise (i.e. turn off the current) then turn on the

power supply and slowly turn the current up to ~ 0.6 A.

2. Put the magnetic field sensor in axial mode, set its gain to 10x and place it along

the central axis of the Helmholtz coil, pushing into the indentation at the center of

the holder. Tare it to set the reading to zero.

3. Start recording magnetic field (press Go) and raise the magnetic field sensor

smoothly along the z-axis until you are above the top coil. Try raising at different

rates to convince yourself that this only changes the time axis, and not the

measured magnitude of the field.

4. Sketch the results for field strength vs. position