explanation of EM wave pattern

用戶31980

2011-06-06 7:03 am

1.some TV signal is transmitted directly from the transmitting aerial to a hose.when an aeroplane flies horizontally over a house towards the transmitting aerial, the TV signal changes alternately from maximum. explain
2.a student places a convex lens made of paraffin wax in front of a microwave transmitter. a receiver connected to a loudspeaker is moved behind the lens. at a particular position, the loudspeaker gives a loud sound, indicating that strong microwaves are detected. explain

回答 (1)

天同

2011-06-06 7:57 am

✔ 最佳答案

1. This is due to interference between the TV signals that directly reaching the house from the aerial and the signals reflected by the flying aeroplane.

When the path difference between the two signals (direct and reflected signals) is a whole multiple of wavelengths, constructive interference occurs, and a maximum signal intensity will be obtained at the house.

2. The parafin convex lens refracts the microwave when it passes through the lens. At position where the "image" of the microwave transmitter is formed, a strong microwave signal is received because all the refracted microwave is focussed by the lens at the "image" position.

👍 0 👎 0