Materials

Galvanometer Compass

200 turn coil Cow Magnet

2 x banana plug cable

Introduction

When Michael Faraday first heard of Hans Christian Oersted's discovery of electromagnetism in 1820, he was intrigued. In electromagnetism, a current produces a magnetic field. Faraday wondered could the opposite happen? Could a magnetic field cause a current? He spent 11 years searching until when disassembling an apparatus after an unsuccessful experiment, he found what he was seeking.

Procedure and Questions

1. Set-up

Note: For a later section of this activity it is important that you connect the apparatus as specified. So take your time and set up the apparatus correctly.

This activity will make use of a galvanometer. A galvanometer is a very sensitive ammeter. You’ll note that the terminals on the galvanometer are labeled + and -. When current flows into the + terminal and out of the – terminal of the galvanometer, the needle will deflect to the right, and when current flows in the opposite sense the needle will deflect to the left.

Notice how the turns are oriented on the 200 turn coil and which end of the coil is connected to which plug. For reference purposes, call the end of the coil nearest you the front. Position the coil so that it is in front of the galvanometer with its opening perpendicular to the face of the galvanometer. Also, orient the coil so that the turns going from front to back turn in a clockwise direction. This is called being wound in a right hand sense. Connect the front of the coil to the + terminal on the galvanometer and the back of the coil to the – terminal on the galvanometer.

Use the compass to identify the N and S pole of the cow magnet. Remember the N pole of a magnet will repel the N pole of the compass. Don’t bring the strong cow magnet too close to the compass or it will attract the compass needle no matter which side is brought near. Label the N pole of the magnet for reference.

2. Observations

Quickly insert the N pole of the cow magnet into the front of the coil and observe the needle of the galvanometer. Quickly pull the magnet back out and observe the needle of the galvanometer.

Q1) What happened to the needle of the galvanometer when the magnet was inserted?

Q2) What happened to the needle of the galvanometer when the magnet was pulled back out?

Reverse the direction of the magnet and try again.

Q3) Did you see any difference when you reversed the orientation of the magnet.

Repeat your observations for both orientations on the other side of the coil and summarize your results in the table below. You should have a total of 8 observations. Leave the last two columns blank for now.

Side of Solenoid (Front or Back)	Pole (N or S)	Direction of Magnet (into or out of the solenoid)	Direction of Needle on Galvanometer (R or L)	Sign of current (+/-)	Induced Pole (N/S)

Q4) List the cases where the galvanometer needle deflected to the left and to the right in the table below.

Left

Right

Q5) Sketch diagrams for the cases where the galvanometer needle deflected to the left. Be sure to indicate the orientation of the magnetic field and the direction of travel of the magnet. Use your diagrams to explain how the situations that produced a deflection to the left are similar.

Q6) Sketch diagrams for the cases where the galvanometer needle deflected to the right. Be sure to indicate the orientation of the magnetic field and the direction of travel of the magnet. Use your diagrams to explain how the situations that produced a deflection to the right are similar.

Q7) If the magnet just sits inside the coil, do you see any deflection of the galvanometer?

Q8) What is happening to the magnetic field in the coil when you do see a deflection of the galvanometer needle?

Question 8 is the essence of Faraday's law and why it was so difficult for Faraday to find it. In his experiments Faraday had used steady magnetic fields to try and produce a current, but it is a changing magnetic field that produces a current.

Lenz's Law

You should have noticed that there is a pattern when the deflection of the needle of the galvanometer is to the left or the right. The result is known as Lenz's law.

Identify the terminals labeled + and – on the galvanometer. When a positive current flows into the terminal labeled +, it will produce a deflection of the galvanometer needle to the right.

Identify for each of your observations whether the current is + or – and fill in the column of the table above for the sign of the current.

Q9) When you insert the magnet in the coil you produce a current. What does a current in a coil produce?

Q10) Use the direction of current flow in the coil and your right hand rule for a solenoid to determine the direction of the magnetic field induced by the current for each of the eight observations you made above. For each of the 8 cases, label the pole induced on the side of the coil where the magnet is being moved in the last column of the table above.

Q11) In all cases when you inserted a N pole, what pole was induced on the side where you inserted a N pole?

Q12) Would the induced pole try to attract or repel the inserted N pole?

Q13) In all cases when you removed a N pole, what pole was induced on the side where you removed a N pole?

Q14) Would the induced pole try to attract or repel the removed N pole?

Q15) In all cases when you inserted a S pole, what pole was induced on the side where you inserted a S pole?

Q16) Would the induced pole try to attract or repel the inserted S pole?

Q17) In all cases when you removed a S pole, what pole was induced on the side where you removed a S pole?

Q18) Would the induced pole try to attract or repel the removed S pole?

Q19) Note that whenever you inserted a pole a like/opposite (circle one) pole was induced, which would attract/repel (circle one) the inserted pole.

Q19) Note that whenever you removed a pole a like/opposite (circle one) pole was induced, which would attract/repel (circle one) the removed pole.

Q20) Lenz's law is the observation of how the direction of the induced field compares to the direction of the inducing field. The directions are _____________.