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A silicon diode, when it is forward biased there is a drop of .7v. but when we use multimeter to measure this drop across diode, it gives zero reading show a short ckt. why?:?:
Because the current level used to detect the diode is very low. For the diode forward bias voltage drop to be about 0.7 V, the current level is relatively much higher.
Usual DVM on diode test position when you measure ordinary Si diode forward voltage drop should show a voltage of about 500 mV. Significantly different readings shows that diode is defective.
The analog multimeter don't show any deflection because it is not able to bias the diode alone but the digital multimeter with diode tester can give the result ...
think of a basin n jug concept.
basin --> network
jug --> diode
water --> current
force of water --> voltage
now, the jug is kept in basin which both are empty (just imagine). u supposed to fill the basin thru jug. i.e., u keep the water pipe into jug. as soon as the jug fills completely, water overflows into the basin and basin space starts to fill with water.
** water does'nt goes into basin untill unless first filled completely by jug.
the same is the case with voltage ax diode also. the diode need to be forced bya min of 0.7 V(si) to allow the current to be passed thru it.
** the diode is empty, which must fist be given a +ve 0.7 volts
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