Newton v Huygen Flashcards
Newtons explanation of refraction
the corpuscles travelled faster in a denser medium like glass because the particles of light were attracted towards the glass surface by an attractive force that increased the vertical component of the velocity leaving the horizontal component unchanged causing it to speed up. The velocity after leaving the glass would be the same as when entering as it would slow back down
Newton’s theory was accepted because
of his scientific pre-eminence, the fact that there was no evidence that light travelled slower in water as Huygen had said, the fact that Huygen considered light as longitudinal so couldn’t explain polarisation
Two differences between both theories
Newton considered light as particles/corpuscles while Huygen considered it in terms of longitudinal waves; Newton said that the light would travel faster in a denser medium whereas Huygen said it would slow down
Why did Newton think light was made of tiny corpuscles
because light was known to travel in straight lines while waves were known to bend via diffraction
Newtons explanation of reflection
He believed reflection was due to a force (F=ma) that pushed the particles away from the surface like a ball bouncing off a wall
What was Huygens wave theory
every point on a wavefront may be considered to be a point source of secondary wavelets spread out in the forward direction at the speed of the wave. The new wavefront is the surface that is tangential to all of these secondary wavelets.
How was Huygens theory proved to be true:
Young’s double slit experiment
Why wasn’t Huygens theory accepted after Young’s experiment
Huygens had proposed that light was a longitudinal wave (like sound) but this couldn’t explain double refraction. A decade later Young realised that transverse waves could explain the behaviour of light. Following this, other scientists agreed with Huygen that light was a wave.
Explain why Newton explained the refraction of a light ray when the light ray passes from air into glass
- particles of light attracted towards glass sirface
- perpendicular ocmponent of velocity increases
- horizontal component unchanged
- speeds up
- he assumed that v1sini = v2sinr and so as i>r v1
- he concluded that the refracting medium exerted an attractive force on a corpuscle increasing its perpendicular velocity component and therefore speeding it up
What was wrong about Newton’s assumption that v1sini = v2sinr
n1sini = n2sinr
n1/n2 = sinr/sini = v2/v1
so v1sinr = v2sini
Describe the fringe pattern observed in Young’s double slit experiments and explain why it could not be explained by Newton’s theory of light
- bright and dark fringes
- evenly spaced
- Newton’s theory consisted of corpuscles which predicted that the light would pass through a slit and form a bright fringe and so two slits would produce two fringes
- However more than two fringes observed + dark fringes (cancellation) cannot happen with corpuscles so Newton’s theory rejected.
