雅思阅读真题+题目+答案：Three ways to Levitate a Magic Carpet

雅思阅读真题+题目+答案：Three ways to Levitate a Magic Carpet

It sounds like a science fiction joke, but it isn’t. What do you get when you turn an invisibility cloak on its side? A mini flying carpet. So say physicists who believe the same exotic materials used to make cloaking devices could also be used to levitate tiny objects. In a further breakthrough, two other research groups have come a step closer to cracking the mysteries of levitation.

Scientists have levitated objects before, most famously using powerful magnetic fields to levitate a frog. But that technique, using the repulsive force of a giant magnet, requires large amounts of energy. In contrast, the latest theories exploit the natural smaller amounts of energy produced by the quantum fluctuations of empty space.

In May 2006, two research teams led by Ulf Leonhardt at St Andrew’s University, UK, and John Pendry at Imperial College, London, independently proposed that an invisibility cloak could be created from exotic materials with abnormal optical properties. Such a cloaking device – working in the microwave region – was manufactured later that year.

The device was formed from so-called ‘meta materia Is’ exotic materials made from complex arrays of metal units and wires. The metal units are smaller than the wavelength of light and so the materials can be engineered to precisely control how electromagnetic light waves travel around them. They can transform space, tricking electromagnetic waves into moving along directions they otherwise wouldn’t,’says Leonhardt.

Leonhardt and his colleague Thomas Philbin, also at St Andrew’s University, realised that this property could also be exploited to levitate extremely small objects. They propose inserting a metamaterial between two so-called Casimir plates. When two such plates are brought very close together, the vacuum between them becomes filled with quantum fluctuations of the electromagnetic field. As two plates are brought closer together, fewer fluctuations can occur within the gap between them, but on the outer sides of the plates, the fluctuations are unconstrained. This causes a pressure difference on either side of the plates, forcing the plates to stick together, in a phenomenon called the Casimir effect.

Leonhardt and Philbin believe that inserting a section of metamaterial between the plates will disrupt the quantum fluctuations of the electromagnetic field. In particular, metamaterials have a negative refractive index, so that electromagnetic light waves entering a metamaterial bend in the opposite way than expected, says Leonhardt.That will cause the Casimir force to act in the opposite direction – forcing the upper plate to levitate. The work will appear in the New Journal of Physics.

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Questions 1-5

Do the following statements agree with the claims of the writer in Reading Passage 3? Write

YES if the statement agrees with the writers claims

NO if the statement contradicts the writers claims

NOT GIVEN if it is impossible to say what the writer thinks about this

1  A mini flying carpet is a possibility according to some scientists.

2  Cloaking devices can be used for levitation.

3  Scientists now know all about levitation.

4  Things can be transported from place to place using empty space technology.

5  The most recent research into levitation has made use of large magnets.

Questions 6-10

Choose the correct letter, A, B, C or D.

6 Ulf Leonhardt and John Pendry

A worked together on a project in 2006.

B both came up with the same idea.

C invented the microwave oven.

D used only basic objects in their research.

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