This is an interactive activity using \"Faraday\'s Electromagnetic Lab\" at http

Question

This is an interactive activity using "Faraday's Electromagnetic Lab" at https: //phet.colorado.edu/en/simulation/faraday (just click on the link in this PDF file). It is fun and great for hands-on learners, and w not take as much time as it looks at first. Please start the simulation and orient yourself. You can click on any of the five tabs labeled Bar Magnet Pickup Coil, Electromagnet, Transformer, and Generator. For the Bar Magnet, you can drag a compass around to get a feel for the magnetic field. You can also select Show Field Meter to measure the strength of the magnetic field. For Pickup Coil, you can move the magnet through a co loop to either light a bulb or affect a voltmeter. For the Transformer, you can move an electromagnet near a coil loop and see what makes the light bulb shine most brightly. Feel free to play around with the simulation. When you are done, click Reset All before beginning Part A. (a) Select the Bar Magnet tab. Deselect Show Compass, and drag the bar magnet to the center of the screen. Then, select Show Field Meter, which allows you to measure the strength of the magnetic field at any location. You should see something like the image at right. Where is the magnetic field strongest, and why? (b) Select the Pickup Coil tab, and place the bar magnet inside the coil containing two loops. Try to find a location where the stationary magnet induces a current in the coil and causes the light bulb to shine. Can you find such a location? If so, where is t and why is that the correct location? If not, why can you not find such a location? (c) Now, let's look at a situation with changing flux. Starting from the far left of the screen, move the magnet to the right so it goes through the middle of the current loop at a constant speed and out to the right of the loop. You should see something like the image at right. The brightness of the light bulb is depicted by the length of the rays emanating from it. Roughly where is the magnet when the light bulb is the brightest, and why?

Explanation / Answer

a.) The field is strongest near the poles of the magnet, as all the magnetic field line converge or diverge there. Hence the lines are higher in number near the poles, that indicate high field strength.

b.) Such a location cannot be found because it is the change in the magnetic field felt by the coil that induces a current in it. Keeping the magnet at a fixed position will give a constant magnetic field around it and hence no current will be induced in the nearby coil.

c.) The light bulb is brightest just before the magnet enters the coil and just after it leaves it.

The emf induced in the coil (due to moving magnet) is given as rate of change of flux through the coil. Flux is given as B.A, where B is the magnetic field through the coil and A is the area of the coil. Magnetic field entering the coil is maximum when the poles are near the coil (as magnetic field strength is highest near the poles).

The light bulb flickers when the magnet is inside the coil because there the induced emf changes its sign rapidly.

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