PHYSICS -ELECTRICITY

2012-05-21 7:27 am

Teddy wants to decorate his room with a filament bulb and an LED. He connects them in parallel to an a.c. power supply. How would the filament bulb and the LED show up?

ans: the bulb lights up continuously and the LED twinkles <---why?? why the light bulb lights up continuously and the LED twinkles?? can anyone help please? thanks!

回答 (1)

天同

2012-05-21 3:52 pm

✔ 最佳答案

LED is itself a diode. It has polarity and is operated under a dc voltage. The current can only flow from the anode (a P-type semiconductor) to the cathode ( a N-type semiconductor), but not in the opposite direction.

If the LED is connected to a ac source, it could only glow when the current is flowing in the right direction, and would stop glowing when the current is in the reverse direction. Hence, you observe that the LED twinkles.

A filament bulb, however, has no polarity. It glows when current is flowing in either direction.

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