How does the chancing magnetic field of me AM radio wave affect the coil? How do

Question

How does the chancing magnetic field of me AM radio wave affect the coil? How does the addition of a ferrite bar help? Experiment Tune the radio to an AM station that comes in clearly, but not too strong. Move towards the middle of the room, away from the metal framed desks. Now 1 slowly rotate the radio about a vertical axis, as in Figure 1. Which directions do the front of I the radio face to give you a strong, clear signal? Which directions is the signal a weak one? I Sketch Given the variation you have observed, use the relationship between the Electric and Magnetic fields and determine along which directions?) the velocity of electromagnetic waves is. Knowing that, where docs this imply the radio station lies? Sketch a diagram to show how the electric and magnetic fields are oriented for a wave coming from some direction, and sketch how the radio (and its coil antenna) should be oriented in order to get the best and worst signal. Prediction Tunc the radio to a station, and turn it so that you get deccnt reception. Suppose you were to rotate the radio counter-clockwise as in Figure 2. Would the signal fade at some points of the rotation (which?), or would you always receive a signal? Explain your reasoning. Think about it. make your prediction, and then test it. Does the rotation cause the predicted variation? Question Knowing how the signal varies with angle, how do you think a car receives AM radio stations from all directions? There is a fairly simple solution to this problem.

Explanation / Answer

Coil antenna works as a folded dipole and has a radiative pattern that is a thorus around (perpendicular ) the coil plane.

The ferrite load increases its effective area.

Because the radiative pattern is a thorus

a) rotating the loop around its axis does nothing at all since it's rotatitonally symmetric.

b) there are nulls of the pattern in the axis plane where reception is null too

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