PHYSICS LDR

[Usman17]

Hey everyone...
Guyz i am pretty confused about the way LDR works :S
Somewhere it says that due to high voltage the bulb is able to light up and somewhere they say since the resistor is low so more current passes thru it which lights up the bulb so how come the bulbs work at night widout any current as at night ldr has high resistance... :S :S :|
soooo confused plz sum1 give a detailed answer to this problem... :|

 

[insomniac]

see ldrs are not common bulbs for home appliances .. ldrs are light detectors .... when the light falling on them is bright the electrons will flow and current passes this is high value current .. this is how the resistance will fall .. the increased current lights the lamp ..... going in details of semiconductors n lattices arent a part of our syllabus ... proceeding .. when its dark the value of current falls and resistance is high

 

[CaptainDanger]

Don't Confuse yourself....


Give this a reading


HERE


If you still didn't get it then I will explain...

 

[Usman17]

@Captain Danger: Yeah but the bulbs that automatically come at night it is written in the book that they also use ldr... As the LDR has high resistance at night so there is high voltage across it and the base current will have sufficient voltage so it will light up the bulb... :| Sometimes current lights up the bulb other places voltage lights it up I am hell confused... :S
Okay i will give it a reading!!

 

[princesszahra]

these are light detectors and their resistance is inversly proportional to light
thats all u need to know at ur level

 

[CaptainDanger]

LDR is mainly used in the potential divider circuit... Where the OUT put voltage depends on the light intensity (due to resistance)... When the output voltage is well enough it will drive a current in the other part of the circuit which results in lightning of the bulb...