Which of the statements about prism binoculars is/are correct? They I. are a pair of two telescopes mounted…

Analyze the question: We need to decide which of the four statements about prism binoculars are true.

Concept: Prism binoculars use two refracting telescopes, one for each eye. Between the objective and the eyepiece of each telescope there are two right-angled (Porro) prisms. Each prism uses total internal reflection.

Checking each statement:

• I. A pair of two telescopes mounted side by side: TRUE. Binoculars are two identical telescopes, one for each eye.
• II. Reduce the optical path of the light ray from the objective to the eyepiece: TRUE. The prisms fold the light path by reflecting it several times. This makes the instrument much shorter than a single-lens telescope of the same focal length.
• III. Present an inverted and diminished image: FALSE. The prisms are there to correct the inversion, so the image is not inverted. It is also not diminished.
• IV. Present an erect and magnified image: TRUE. The prisms invert the image again (both top-to-bottom and left-to-right), so the final image is erect. The telescope action makes it magnified.

So statements I, II and IV are correct, and III is wrong.

Answer: Option D (I, II and IV only).

Tip: Remember the two jobs of the prisms in binoculars: shorten the instrument and make the image erect. Any statement saying the image is "inverted" or "diminished" is a trap.