Final answer:
The intensity of unpolarized light after passing through an ideal polarizer is reduced to half of its original value (I0/2).
Step-by-step explanation:
If unpolarized light of intensity I0 passes through an ideal polarizer, the intensity of the emerging light will be I0/2. This phenomenon occurs because an ideal polarizer will only transmit the component of the light that is aligned with its polarization axis. Since unpolarized light consists of waves vibrating in all directions equally, only half of the intensity will get through when aligned with the polarizing filter's axis.