✔ 最佳答案
Of course yes. If the image cannot be seen, it is not an image.
Image that formed on the same side of the object is a virtual image. It is because of the refraction of light through the lens that enables the observer to see the image through the lens.
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1st:Ultrasounds travel faster than audible sound in the same medium.
No. Under the same temperature, both ultrasound and audible sound travel at the same speed through a given medium.
2nd:Ultrasound has a frequency higher than that of audible sound.
Yes. As the name implies, ultrasound is sound wave with frequencies higher than audible sound, i.e. with frequencies higher than 20 000 Hz
2010-03-29 12:55:20 補充：
For your further question: of course not. Light from the object goes in the direction onto the lens. You won't be able to see the refracted light if you look on the side of the object. What you could see is only the very dim image formed by REFLECTION on the lens surface.
