Magnetic Pendulums

Oscillations in the right pendulum triggers oscillations in the left one. These pendulums oscillate in phase or out of phase based on the nature of magnetic field. Let us explore the basic setup first. This plastic spool is wound with 36 gauge coated copper wire Almost 3000 tons. Around 1 meter of wire is kept loose from both ends. This extended wire can be used to connect the coil to the multimeter or LED. With the help of a pencil and spoke we can hang it like this. Our pendulum is ready. Let us connect both ends to the LED after removing insulation. Four neodymium magnets are attached to the bottle stand with the help of a long screw. North pole is marked with a red dot. With this arrangement plastic spool can oscillate freely with a magnet in the center. When the pendulum oscillates LED glows. Let us position it like this so that we can watch it closely. As a result of an oscillating coil current is induced. As it approaches and leaves the strong magnetic field LED glows when the coil moves towards the right. If we switch the polarity of the magnetic field LED glows when the coil moves towards the left. Keeping the magnets right in the middle of the coil ensures that change in magnetic field is strong enough to glow the LED in both directions. Will the coil oscillate the same way when I connect these two ends? Let us try. After a couple of oscillations pendulum stops. What could be the reason for this? Changing magnetic field induces current in the coil turning it into an electromagnet. Based on the polarity magnetic fields interact and pendulum stops. We can explore the interaction of these forces by changing the strength of the magnetic field as well. Coil oscillates for longer duration with only couple of magnets. Now let us bring in another such pendulum. We will connect open ends of both the pendulums so that coils are connected. The wires now form a continuous loop. When the coil on the right oscillates current is induced in it which also flows through the coil on the left. It acts as an electromagnet and interacts with the magnetic field nearby. As a result it also starts oscillating. Right now two coils are oscillating in phase. We can change the direction of magnetic field by switching magnets. This time coils are oscillating out of phase. Let us work with a single coil to no more. We will replace LED with a multimeter. EMF is induced as coil oscillates Induced current also changes direction as can be seen with the changing sign on the multimeter. Expected reading for this setup was more than 1.5 volt. But it looks like multimeter is not sensitive enough to record this in a short span. How about the amount of current induced? Amount of current induced decreases as oscillations slow down. Let us bring in external power supply in the form of two pencil cells. When current is momentarily passed through a coil it becomes an electromagnet. Direction of current flowing through the coil is anticlockwise. Similar poles repel hence it moves to the right. We can change the direction of magnetic field. With the same direction of current coil should move towards the left as opposite poles attract. You can try changing the strength of magnetic field by changing the number or type of magnets on either side. Change the number of turns keeping the strength of magnetic field same. Try with different shapes of coil as well as the magnets. Switching the connections between two coils also change the oscillating pattern. Do try this at home. Thank you.