Electromagnetic induction can-be used to make a microphone and a speaker. A micr

Question

Electromagnetic induction can-be used to make a microphone and a speaker. A microphone is a device for converting sound energy into electrical energy and a speaker is a device for converting electrical energy to sound energy. Look closely at the hand-made microphone and speaker you have been provided (coils glued on a cardboard with a magnet, close to it) and speak into the microphone (make sure to put your mouth very close; to the microphone paper. If you can not hear your voice on the "homemade speaker", lightly tap or scratch on the microphone surface with your finger). What is the moving part of the microphone? The speaker will convert the electrical signal back into sound (and the amplifier provided will amplify it). Explain the process via which the microphone is converting sound into an electrical signal describing the roles played by the cardboard, coil and the magnet. (Set-up P111-18A.pdf) (b) Since the hand-made microphone may not work very well, speak into the commercial microphone and listen to the sound in the speaker. Does the hand-made speaker work as desired? Write down the feature of this experiment, that you like best. Also, write down two other applications of electromagnetic induction in your everyday experience. (a) You are provided with two long vertical hollow tubes made with different metals. If you drop a magnet and a metal piece (slug) both of which have identical shape through each tube, which of them will come out of the other end in shorter time? Explain your reasoning. Also, predict what should happen to the weight of the long vertical tubes while the magnet or slug is falling through it (set-up P111-18B.pdf). Explain your reasoning.

Explanation / Answer

(1) (a) Mostly, the microphone has three main parts - Diaphragm, coil and a magnet. When we speak, the sound waves created due to vibration of air particles hit the diaphragm and make it vibrate along the coil. The coil is moving inside the magnetic field produced by the small magnet. It generates a small magnitude AC current which goes to microphone end terminals. We can also amplify it by using amplifier. Now , as you have done this experiment in lab using cardboard, coil and magnet. Now, it must be clear that in your case, cardboard is acting as diaphragm which must be in contact with the coil placed in magnetic field of the given magnet.

(1) (b) Now, I will tell some of the applications.The first and foremost use of EM induction is to produce electricity which is like a lifeline for us. Electricity is produced by placing coils of wire inside the magnetic field.

You must be having a credit or debit card. You must have seen a black strip on the reverse side. Yeah, that is a magnetic strip. Its again a daily life example of EM induction, Walk through checkpoints at airports, bus stands, malls. This list is so big. Most of the things we use in daily life undergo EM induction.

(2) (a) In both the cases, The metal piece (slug) will come out of the other end in shorter time while magnet will take some time and will come out later. The reason for this, when a magnet falls through the tube, its magnetic field is contantly changing position while falling, it induces the flow of eddy currents. These eddy currents create a magnetic field which exert force on the falling magnet and oppose the magnet's fall.

Talking about the weight, the weight of the tube will increase when magnet is falling through it. Actually, If we do the practical, we will see that ,magnet doesn't touch the tube circumference while falling and it doesn't accelerate like other objects. There must be some force acting on the magnet which supports its weight in the tube and according to newton's third law, there must be an equal and opposite force acting on it which will be in downward direction. This downward force will be exerted on the weighing scale which in turn shows increased weight.

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