|
VISUAL PHYSICS ONLINE 7.1 THE NATURE OF LIGHT P71 013 Newton regarded light as being composed of small particles which
were referred to as corpuscles.
How did the model of Newton explain the bending of light as it passes from
one medium to another? Draw a diagram showing the bending of light as it
transverses the interface between air and water according to the Newtonian
model. Draw a diagram showing the bending of light as a light beam
transverse the interface between air and water according to the wave model
given the following parameters: refractive index of air = 1.00; refractive
index of water = 1.33 and angle of incidence = 45o. What are some of the properties of corpuscles and how do they
resemble and differ from Einstein’s photons? Hint: Do a web search on Newton’s particle models of light
and the controversy between the early wave and particle models of light.
https://www.visionlearning.com/en/library/Physics/24/Light-I/132 View solution below only after you have completed answering the question. The solution is not in a form that you would answer in an examination. The answers are in more detail to help improve your appreciation and understanding of the physics. |
|
Solution Around 1700 the Newton, proposed that light was made up of corpuscles (small particles which have mass). Since these corpuscles have mass in Newton’s particle theory for light, he deduced that a beam of light parallel to the surface of the Earth, would bend downward under the influence of Earth’s gravitational field. This means the trajectory of light would be a curved and not a straight line. The fact that we don’t notice this effect is, according to Newton was due to the very high speed of light. Newton was able to explain the geometric properties of light very well with his particle theory by assuming a straight-line propagation of light, as in the ray model of light. Newton explained refraction by suggesting that when the corpuscles light end up in a medium, such as air or water, they are attracted to the particles of that medium due to an attractive force (gravity) between the particles. Inside a medium (e.g. water or air), the light corpuscles are equally surrounded by particles of the medium. As a result, the attractive force pulls an equal amount on all sides making the net force zero. So, there is no effect on the light particles, thus the light keeps going in a straight line, as long as they stay inside the same medium. But there is a difference at the boundary of the media. For example, for light passing from air to water, according to Newton, there is more matter in the water than in the air and so the light particles are more attracted towards the denser medium. As a result, a light beam makes a sudden bend and refraction is created. His explanation seems to work, except that it leads to the prediction that light will travel faster in the more dense medium, which is clearly wrong. The speed of light is slower in the more optical dense medium. Hence, the deflection of the light predicted by Newton towards or away from the normal to the interface is also wrong.
Newton’s particle model – propagation of particles with mass through a medium. Einstein’s model – massless particles called photons propagate through a medium. A photon has
energy that is proportional to the frequency of the associated wave |
