CHAPTER 15 HOW SCIENCE WORKS ASSIGNMENT 1
COMPETING MODELS OF LIGHT
Page 292 of the student book discusses the work of Huygens and Newton in determining
whether light travels as particles or waves. Looking back to this Assignment, answer the
1. What were the optical effects that both Huygens’ and Newton’s models of light were
able to explain? In your opinion, forgetting what you have learned in physics, which
model provides the simplest explanation of these effects?
2. What other work and discoveries of Newton’s might have led him to prefer a particle
3. A crucial test of a theory of light was to measure the speed of light in a medium such
as glass or water.
a) Explain why this was a crucial test.
b) In fact, the test wasn’t carried out until about 50 years after Young first proposed
his theory. By then, most physicists had accepted the wave model of light as being
correct. Suggest some reasons why they had done so.
4. Newton saw that his simple particle model had flaws. For example, when light hits a
glass surface, some of it is reflected and some refracted. To get out of this difficulty,
he added a new feature: the particles must have ‘fits of difficult and easy reflection’.
He didn’t explain why, but it ‘saved the appearances’ – the observed effects.
In a later period in physics, astronomers discovered that the orbit of the planet
Mercury changed in a way that couldn’t be explained by Newton’s laws of gravity. To
save this ‘appearance’, it was suggested that the ‘2’ in the inverse square law should
really be ‘2.000 000 1612’.
Young’s wave theory and Einstein’s relativity theory explained both these effects
using a completely new way of looking at nature.
Do you think that it is legitimate for scientists to make slight adjustments to theory
like this, just to ‘get things right’? (You should be able to think of arguments both for