Introduction
In this lab we will explore several aspects of magnetism. First, we will qualitatively study some of the basic properties of magnetic materials. Then we will observe some properties of electromagnets and explore application of electromagnets to motors and to making a determination of Earth’s magnetic field.
Part I Basic Properties of Magnetic Materials
Procedure
Magnetic poles
Q1) Take two of the ring magnets. Bring the two painted sides together. What do you observe?
Q2) Bring the two unpainted sides together. What do you observe?
Q3) Bring a painted side towards an unpainted side. What do you observe?
Q4) Bring a magnet near the electroscope. Do you see anything? Can we conclude that the force between magnets is not electric? Why?
Q5) How are the properties of permanent magnets similar to the properties of charges?
Any magnet has two sides with opposite properties which we refer to as a magnetic pole. It is customary to call one pole the ‘north’ pole and one pole the ‘south’ pole.
Q6) If the painted sides of the magnet have one type of pole and the unpainted side of the magnets have the opposite pole, then what can you conclude about the magnetic force between like and opposite poles?
Q7) Bring one end of the compass near the painted side of a magnet. How does it behave? (Note bring it close enough to observe an effect but not too close.)
Q8) Bring the opposite side of the compass near the painted side of the magnet. How does it behave? (Note bring it close enough to observe an effect but not too close.)
A magnet like a ring magnet which has two opposite permanent poles is referred to as a permanent magnet.
Q9) Explain how the observations in Q7) and Q8) demonstrate that the compass is a permanent magnet.
Identify North and determine which side of the compass needle points north. We define the pole of the compass that faces north to be the ‘North’ pole of the magnet and the pole that faces south to be the ‘South’ pole of the compass.
Q10) Given your observations about the behavior of the magnetic forces between like and opposite poles, what type of pole is the painted side of the ring magnet and what type of pole is the unpainted side of the ring magnet?
Q11) What type of magnetic pole must Earth’s north pole be?
Temporary magnets
Q12) Bring the paper clip near the painted side of the magnet. What do you observe?
Q13) Flip the paper clip over and bring it near the painted side of the magnet. What do you observe?
Q14) Bring the metal paper clip near the blank side of the magnet. What do you observe?
Q15) Flip the paper clip over and bring it near the blank side of the magnet. What do you observe?
Q16) Does the paper clip always seem to be attracted to the magnet?
Materials which are always attracted to a permanent magnet are known as temporary magnets.
Non magnetic materials
Q17) Bring the painted side of the magnet near the brass ball. Do you observe any thing?
Q18) Bring the unpainted side near the brass ball. Do you observe anything?
Q19) Based on these observations, does the brass ball appear to be either a permanent or a temporary magnet? Explain.
Materials that do not exhibit magnetic properties are known as non-magnetic materials.
Classification of magnetic materials
Q20) Describe a procedure so that you can classify the plastic coated wand, the steel ball, and the aluminum ball as permanent magnets, temporary magnets, or non-magnets.
Q21) Carry out your procedure and record your observations.
Q22) Classify each of the three objects as a permanent magnet, temporary magnet, or non-magnet.
The Magnetic Field of Earth
In this brief activity we will determine the magnetic field of Earth. We will use an apparatus called a tangent galvanometer. The tangent galvanometer is essentially a coil with a compass at its middle.
Procedure and Questions
1. Set-up
Make sure that the DC power supply is turned off, the knob on the right is set to the 0 – 28 V setting and the knob on the left is fully counter clockwise. Connect the coil to the DC output of the power supply between the middle and an outer terminal. This means that the power supply is connected across 5 turns in the coil. Rotate the apparatus so that compass needle is oriented in the plane of the coil. Identify which side of the compass needle points north, and note it for later reference. Rotate the compass case so that the needle aligns with N on the case.
2. Turn on the power supply and very slowly turn up the current. Be careful to monitor the current meter on the power supply and not the voltage. Do not exceed 5 A, and probably you will need considerably less.
23) Do you observe any effect? Describe it.
3. Turn up the current a little more.
24) What change is there?
4. Turn down the current and reverse the leads to the coil. Slowly turn up the current again.
25) Does the effect change in way?
5. Turn down the current and connect the power supply across the outer terminals on the tangent galvanometer. The power supply is now connected across 10 turns in the coil.. Very slowly turn up the current.
26) Was there any change in the effect?
27) When current flows in the coil, what is produced?
28) In the center of the coil, what direction does the magnetic field produced by the coil point compared to the coil?
29) How does the strength of the produced magnetic field depend on the current in the coil?
30) How does the strength of the magnetic field produced by the coil depend on the number of turns with the coil?
31) Draw a vector diagram showing the sum of the magnetic field due to the coil and the magnetic field due to Earth.
32) Use your diagram to find an expression for the angle, q, through which the needle deflects in terms of Earth magnetic field and the magnetic field of the coil.
An expression for the magnitude of the magnetic field,
in units of teslas, at the center of the coil is given by 
, where
B is the magnetic field strength, N is the number of turns in the coil, r is
the radius of the coil, I is the current flowing in the coil, and m0 = 4p x 10-7 Tm/A is a fundamental constant called the
permeability of free space.
33) Describe a procedure to measure Earth's magnetic field using this apparatus.
34) Carry out your procedure and record your results and calculations below.