At the atomic scale, all matter exhibits properties commonly associated with both waves and particles. The classic experiment that demonstrates wavelike properties is the double-slit experiment, first performed by Thomas Young at the beginning of the 19th century. If a beam of light passes through two narrow slits and is projected onto a screen behind the slits, a pattern of light and dark fringes can be observed. The explanation for this is based on an analogy with ripples in water. If we drop two stones some distance apart, the ripples start to interfere with each other, sometimes amplifying when two crests or troughs meet, sometimes canceling when a crest meets a trough. A similar explanation holds for interference effects with visible light; the two slits act as independent sources in the same way as do the stones in water. This experiment provided convincing evidence in support of Christiaan Huygens’s wave theory of light, which eventually supplanted the older particle theory of Isaac Newton. However, in the 20th century, Einstein showed that Newton was not entirely wrong. His analysis of the photoelectric effect showed that light could behave as a particle as well as a wave. Surprisingly, electrons, which we tend to think of as particles, also demonstrate interference effects, showing that they too are waves as well as particles.

Which of the following best summarizes the findings of Young’s experiment, as described in the passage? ​

A​ The waves from independent light sources interact with one another in predictable patterns.  ​
B​ Two light sources can cancel each other out, creating the observed dark fringes. ​
C​ Light exhibits properties of both particles and waves. ​
D​ Newton’s theory was permanently debunked. ​
E​ Newton’s theory was correct all along.



Based on the passage, what would we expect the light fringes in Young’s experiment to represent?

​A​ the light particles from both slits landing on the screen ​
B​ the amplification created by the combination of both sets of waves of light ​
C​ the projection onto the screen where the light is not blocked out by the object with the slits ​
D​ the amplification created by light particles
​E​ the projection onto the screen where the light is blocked by the object with the slits