Experiment 9 Magnetic Field Strength of A Coil: 9.1 Background
Experiment 9 Magnetic Field Strength of A Coil: 9.1 Background
Experiment 9 Magnetic Field Strength of A Coil: 9.1 Background
Lisa Randall
9.1 Background
There are two types of magnet; permanent magnet and electromagnet. A
permanent magnet is an object formed from a material that is magnetized
and creates its own magnetic field, B. A permanent magnet, permanently,
exhibits a magnetic field, B and displays a magnetic behavior. While an
electromagnet is made from a coil of wire which acts as a magnet when an
electric current passes through it. Unlike a permanent magnet, an electro-
magnetic magnet only displays magnetic properties when an electric current
is applied to it. Hence for an electromagnet, the electric currents generate
the magnetic fields, B. The magnitude and direction of the magnetic field, B
generated depend on the specific geometry of the wire, such as a circular coil,
two circular coils, solenoid, in which the current is flowing. In this activity,
we will study the behavior of the magnetic field strength of a circular coil
along the perpendicular axis, X through the center of the coil, C as shown
in Figure 9.1.
For a coil of wire having radius R and N turns of wire, the magnitude of
magnetic field, B along the perpendicular axis, x, through the center of the
coil, C, is given by:
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Figure 9.1: A Single Coil
µo N IR2
B= (9.1)
2(x2 + R2 )3/2
where N is number of turns, I is current, R is radius and x is the distance
from center, C of the coil. For further reading, refer to ?
9.2 Objectives
At the end of the activities, students should be able to:
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9.3 Apparatus
Power Supply (D.C), Magnetic Field Sensor, Ammeter/Voltage-current sen-
sor, Compass and String
9.4 Pre-Lab
1. Write the formula of magnetic fields produced by currents for the fol-
lowing shape.
What is the direction of the magnetic field at the center of the loop?
9.5 Procedure
1. Locate the center, C of the coil as shown in Figure 9.3. Then set-up
the apparatus so that the meter stick will pass through the center of
the circular coil, C.
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Figure 9.3: Center of the Coil, C
2. Then construct the circuit as shown in Figure 9.4. Set the voltage, V
at the lowest possible value (e.g V = 1 V ).
3. Determine the direction of the current, I inside the circular coil. Then,
use the right hand rule and determine the direction of the magnetic
field inside the coil. Verify the result using a compass.
4. Record the value of the current, I1 when the voltage is the lowest
possible value (e.g V = 1 V ).Then measure the magnetic field strength
at x = 0
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Table 9.1: Magnetic Field Strength, B.
I= ±
Position, X/(cm) Magnetic Field, B/(mT)
(x ± ) (B ± )
1.0
1.5
2.0
2.5
3.0
4.0
5.0
6.0