Magnetic fields around electric current

[chris_yau]

I have just done an experiment of magnetic fields around electric current in straight wire by using the seach coil.

I have 2 questions about this...

(1)why is this necessary to ensure the search coil is at the same level as the wire?
My anwser:If the seach coil is not at the same level as the wire, the measurement is not correct. It is because the induced e.m.f. is the greatest around the wire. We should put the seach coil at the same level to have a clear measurement of induced e.m.f.

(2)why the sensitivity of the seach coil can be increased by increasing the frequency?
My anwser:If the frequency increased, the current changed its direction more frequently. Thus, the induced e.m.f will increase. As a result, the seach coil had a increase in sensitivity.

Am I correct??

 

[berkeman]

-1- is okay, but -2- is not quite right, I don't think. Did you actually see an increase in output voltage amplitude of the sense coil for higher primary coil drive frequencies? Was the primary coil drive voltage amplitude changing as well, or was it steady?

 

[chris_yau]

To be frank, it is the question in the report.
Actually, I didn't see the increase of the sensitivity.
The amplitude is steady.

 

[berkeman]

The only effect that I can think of that would make someone think there was increased sensitivity is if the drive circuit for the primary coil couldn't drive the low inductance of the coil at low frequencies. But the transfer function between the primary and secondary coils should not vary with frequency. If there is ferrite or iron or something connecting the primary and secondary, you will get losses that depend on the material.

 

[chris_yau]

Thank you for your help~!