The characteristic bright-line spectrum of an element occurs when electrons

When an electron absorbs energy it becomes excited and moves to a higher energy level called an excited state. This can happen when an atom absorbs light.

Eventually that electron will relax and return to the ground state, which was at a lower initial energy. During this relaxation, the energy that was previously absorbed is now released in the form of light.

This is specifically what occurs during a bright-line spectrum. The excited electrons return to the ground state, which is a lower energy level, and the energy is released as distinct lines of light.

The independent variable is the type of music.the dependent variable is the pulse rate.the intervening variable is the age of the subject.if the mother does not like rock, her pulse is likely to not increase.the same might be true for the sister.the friend may like rap and gets excited.to establish cause/effect relationship, all of the subjects must be consistent.hope i .