has LED resistor? if yes how much?
i connect the 3v battery in led red 5mm and measure current.it would be 60mA.result is 3/60mA=47ohm.is that true?

 

has LED resistor? if yes how much?
i connect the 3v battery in led red 5mm and measure current.it would be 60mA.result is 3/60mA=47ohm.is that true?

As far as I know, there is no "resistance" in LED's. Just like a diode, they have a voltage drop which varies with the current, upto a limit.

In your experiment, the current is limited by the internal resistance of the cattery.

Ramesh

 

Here is a plot of the forward voltage V(f) [Red trace] of a typical Red LED as a function of current between 100uA and 30mA. Because LTSpice can do it, I also plotted V(f)/I(D1) [Green trace, units of Ohms]. What would you say the "resistance" of the LED is?

 

I believe LED and diode resistance is roughly inversely proportional to voltage.
Diodes has dynamic resistance. It's not constant.
Try looking up incremental resistance.

 

LED's have little to no resistance. You forgot to take the forward voltage drop into account. Look at your LED's datasheet, find the forward voltage, subtract it from the actual (measured) battery voltage, and you get (roughly) the internal resistance of the LED. It should be very low.