Magnetic field lines, generated by a long straight wire carrying a current, are circles concentric with the wire and lie in planes perpendicular to the wire.
a. true
b. false

True

Explanation:

It is true that magnetic field lines around a current carrying wire is in the form of concentric circles and lie in the plane perpendicular to the wire.

This Fact can be Proven by placing the iron filling around the wire and they will be arranged like concentric circles and Magnetic field intensity diminishes as we go away from the wire.  

absorption lines are where light has been absorbed by the atom thus you see a dip in the spectrum whereas.

emission spectra have spikes in the spectra due to atoms releasing photons at those wavelengths.

explanation: