Module 7: The Nature Of Light

Question 1

what was Maxwell’s contribution to the classical theory of electromagnetism in relation to

a. unification of electricity and magnetism
b. prediction of electromagnetic waves
c. prediction of velocity

Answer 1

• he developed mathematical equations to show that electric and magnetic fields move at a speed close to the speed of light
• light is a form of electromagnetism
• if a changing electric field is produced, a magnetic field at right angles to this electric field will be produced (they will keep producing each other). this will produce two mutually propagating fields
• both the electric and magnetic fields would necessarily oscillate at the same frequency
• the electromagnetic radiation would be self-propagating, independent of its generator, and could extend outwards into space as an electromagnetic wave of fixed frequency

Question 2

describe the production and propagation of electromagnetic waves

Answer 2

THIS CARD IS NOT DONE

Question 3

what is spectroscopy and what can it be used to find

Answer 3

spectroscopy: the investigation of the spectra produced when matter interacts with or emits electromagnetic radiation
- continuous spectra: shows the continuous visible light spectrum
- absorption spectra: continuous spectrum with certain bands (frequencies) missing as they have been absorbed
- emission spectra: shows the frequencies missing from the absorption spectra once they have been emitted

analysing spectra can help us find:

• surface temperature: using wien’s law, the peak wavelength indicates the surface temperature of a star
• chemical composition: by analysing the missing frequencies from the absorption spectrum
• rotational and translational velocity: redshift indicates moving or spinning away from earth, blueshift indicates moving or spinning towards earth. the broader the absorption bands, the faster the tar is rotating
• density: the radius of a star can be determines with the help if it spectrum. density can then be calculated by mass/volume

Question 4

what models of light were proposed by Newton and Huygen?

Answer 4

Huygen: Wave Model
- described light as a type of wave, similar to the water waves observed in the ocean

Newton: Particle Model
- argued that reflection and refraction could only be explained if light were made of particle, or ‘corpuscles’, with each different colour of the spectrum representing a different type of particle

Question 5

what evidence supports Huygen’s wave model and what resistance was there to the model

Answer 5

EVIDENCE: properties of light (diffraction, interference and polarisation) can only be describes using the wave model

• diffraction: light bends when it is passed through a narrow opening or when it travels around an obstacle
• interference: young’s double slit experiment shows light diffracting and interfering to produce an interference pattern
• polarisation: when a transverse wave is allowed to vibrate in only one direction and it passes through a polarising filter oriented on an angle, the intensity of the wave will decrease

LIMITATIONS:

• Poisson (a french scientist) argued that if the mathematical principles used to explain young’s double slit experiment were applied to light shining on a round disk, there would be a bright spot in the shadow created by the disk and since no one had observed this yet, the principle must be wrong
• however, one of his colleagues carried out this experiment and observed a bright spot which again proved the wave model right