# Alternating current

In an LR circuit with alternating current , it is know that the inductance of the cable is of the order 10^-7 . With a 2 ohm resistor ,the circuit is used to measure inductance.There are 2 frequencies , 100kHZ and 1M Hz,that can be chosen for the measurement .
So whyI MHz is better . I know that it is beacause order of magnitude of reactance is comparable to that of resistor.But why is it better ??

Thanks!

## Answers and Replies

marcusl
Science Advisor
Gold Member
It would be clearer if you provided details of the measurement method. If you are looking at the phase shift between the current and voltage, then it is easiest to measure when the resistance and reactance are comparable.

I see your point.Thanks

The impedance of an inductant depends on the frequency, the higher the frequency, the larger the impedance. In your case, the inductance of the cable is of the order 10^-7 which is quite low, so we should use the 1MHz frequency for measuring to have better output.