Sunday, August 7, 2011

On Electromagnetic Induction

Ok. This might have been the worst possible meeting to be late, and unfortunately, my friend Mac and I were. Because we had to finish our summary report, we were around ~25 minutes late, and the post-experiment quiz was almost over. Thank God Sir was kind enough to let us answer the whole quiz, but, still, I think that my grade in that quiz is low. I was quite clueless during the quiz, with sweat dripping because we were running before we entered the classroom. I just hope that I passed the quiz.

What's done is done, so let's move on.

Our experiment this meeting was all about electromagnetic induction. What this phenomenon means is that changing the magnetic field around a wire induces a current and emf in it. By Faraday's Law, this induced emf is equal to the negative time derivative of magnetic flux. By Lenz Law, we can note that the direction of the induced emf or current is in the direction opposite the cause of it. Therefore, if a magnet (N pole facing the coil) is put nearer to the coil, an emf and current will be induced in the counterclockwise direction, since the coil will resist the magnetic field on it due to the magnet by producing an upward magnetic field itself.

The experiment proper was quite short, because it only involved one set-up (solenoid) with different 'twists'.

This meeting introduced us, physics students, to a new measuring device ---- the GALVANOMETER. From wikipedia, a galvanometer is a type of ammeter that produces a rotary deflection of some type of pointer in response to current flowing through its coil. Using the galvanometer was the first part of the experiment. Here, I also learned (from the handout) that humans are considered large resistors. :O

We, then, looked at the effects of probing a moving magnet at the hollow part of the solenoid. It was observed that the faster the magnet was "swiped", the higher the magnitude of the deflection on the galvanometer. When it was put into the solenoid, the deflection was to the right. When it was pulled out, the deflection was to the left.

We, then, put different metals (iron, copper, aluminum) on the hollow part of the solenoid. We saw how the magnets affected the deflections on the galvanometer, and I think that it has something to do with the types of magnet because each of which was of a different type (ferromagnet; diamagnet; paramagnet).

Lastly, we looked at the effects of putting a smaller solenoid in the middle of the solenoid, and withdrawing the smaller solenoid a centimeter at a time until it was completely outside. This was the part that was quite a source of confusion because the procedure dictated that we had to start at the point when the smaller solenoid was completely inside the solenoid. There was some space between the two solenoids that was not accounted for, but we figured it out.

This experiment was relatively easy because it was quite straightforward. Compared to the past experiments that we had, this was one of the quickest to be accomplished.

Lesson learned today: don't be late. I want to repeat it to myself. Don't be late.