Physics laboratory experiment: Electromagnetic Induction

Question

hi there. i would like to ask help on answering from our laboratory experiment. maybe some of you have done this experiment already?

this experiment is on electromagnetic induction. after performing the experiment, we were able to produce a graph of "Average Galvanometer deflection vs length of the Primary Solenoid inside the Secondary Solenoid"?

sounds familiar?

There are five questions at the end of the experiment:

1.) in all procedures of the induction experiment, observe that there always involved either the motion of the magnet (fast or slow) or the power supply state (on or off). Explain briefly why these mechanisms are necessary.

2.) consider a solenoid connected to a galvanometer. what will be the deflection of the galvanometer if the N-pole of a magnet is moved towards the solenoid? what will be the effect on the deflection of the galvanometer if the S-pole of the magnet is moved towards the solenoid instead. Explain briefly.

3.) consider a bar magnet dropped through a loop of wire connected to a galvanometer. (the normal of the loop is parallel to the direction of the drop.) describe and discuss briefly what would be observed on the galvanometer (i.e. strength and direction of deflection) as:

a.) the magnet enters the loop

b.) the magnet is in the middle of the loop

4.) describe the charge of the flux through a loop of wire rotated in a uniform magnetic field. relate the change in flux to the induced current in the loop. explain.

5.) motors convert electrical energy to mechanical energy. generators, the reverse, convert electrical energy to mechanical energy. give your briefest and simplest illustration or explanation on why these machines are possible.

---> i hope you can help me understand the concept of electromagnetic induction, that's why i posted this.

thanks.

Very Happy

source:

physics 72.1 laboratory activity manual

2007 edition

College of Science

National Institute of Physics

University of the Philippines - Diliman

a very similar lab experiment can be viewed at:

http://www.rowan.edu/colleges/lasold/physicsandastronomy/LabManual/labs/ElectromagneticInduction.pdf

Answer 1

The key idea of electromagnetic induction is a changing magnetic field relative to the charges (free electrons) in a conductor. This can happen when a conductor is moved relative to a stationary field, a field (e.g., a magnet) is moved relative to a stationary conductor, or the field strength is varied in the presence of a stationary conductor. Electromagnetic induction doesn't occur with a steady, unmoving magnetic field and a stationary conductor.

With this in mind, I think you can see why the current has to be turned on or off, and there's no galv. deflection when the current is steady; or the magnet has to be moved. (If the power supply were AC, you'd have a continuously varying field, and you wouldn't have to turn the current on and off, but galvanometers respond poorly to AC; you'd need an AC voltmeter.)

Answers to questions 2-6 involve a lot of thought and knowledge of the details of the experiment (e.g., which way the solenoid is connected to the galv.). Rather than my doing all the thinking for you, below are several references that will clarify the concepts you need to know. See, especially, Faraday, Lenz refs. for magnet-solenoid interaction.