Question

Which one of the following is not a characteristic of a simple two-lens astronomical refracting telescope? a) The final image is virtual. b) The objective forms a virtual image. c) The final image is inverted.

Short answer

a) The final image is virtual. b) The objective forms a virtual image. c) The final image is inverted. Answer: b) The objective forms a virtual image.

Step-by-step solution

Understanding a simple two-lens astronomical refracting telescope

A simple two-lens astronomical refracting telescope consists of two lenses: the objective lens and the eyepiece lens. The objective lens gathers the incoming light from a distant object and forms an image that is further magnified by the eyepiece lens for the observer to see. The objective lens is usually bigger and has a longer focal length, while the eyepiece lens is smaller with a shorter focal length.

Examining statement a: The final image is virtual

In a refracting telescope, the final image seen through the eyepiece is virtual. This means it cannot be projected on a screen, but only seen through the eyepiece. This is because the final image is formed by rays that appear to come from the point where the image is formed, but haven't actually passed through that point. Since the rays only appear to come from that point, the image is virtual. Statement a is true.

Examining statement b: The objective forms a virtual image

The objective lens of a refracting telescope gathers the incoming light from a distant object and forms a real, inverted image on its focal plane. This image is then further magnified by the eyepiece lens. Since the objective lens forms a real image, this statement is false.

Examining statement c: The final image is inverted

When light passes through the objective lens, it forms a real, inverted image on its focal plane. The eyepiece lens then further magnifies this already inverted image. As a result, the final image seen through the eyepiece of a simple two-lens astronomical refracting telescope will also be inverted. Statement c is true.

Conclusion

Based on the analysis of the statements, we can conclude that statement b ("The objective forms a virtual image.") is not a characteristic of a simple two-lens astronomical refracting telescope.