Electromagnetic Spectrum: A High School Physics Module, Study notes of Physics

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Physics 12; Summaries; Module 7

Electromagnetic Spectrum

Conduct investigations of historical and contemporary

methods used to determine the speed of light and its

current relationship to the measurement of time and

distance:

• Contributing scientists: ○ Galileo ■ First known person to attempt to measure the speed of light ■ Stood on hilltops with a known distance between them. Both him and his assistant had lanterns. Galileo uncovered his lantern, and when his assistant saw the light, he immediately uncovered his lantern. Galileo noted the time he saw his assistants light. ■ He concluded the speed of light was at least 10 times that of the speed of sound, and also that his results would be inaccurate due to the time delay of human reaction ■ Proposed a method of telling time aboard a sea vessel: Observing Jupiter’s moon, Io, coming in and out of eclipses, which were thought to be predictable, but later found to be inaccurate. ○ Romer ■ Noticed that the variation in times of the eclipses (<16. minutes) coincided with the times that Jupiter was closer to/further from Earth, as a result of their different orbital speeds ■ He explained that the variations were a result of light having to travel across Earth further or lesser. ■ Made a rough estimate that it would take light 11 minutes to travel from the Sun to the Earth (2.1x10^8 ms-1) ■ However, due to the fact that Earth’s orbit was not accurately known, the result was incorrect. ■ However, he became the first person to suggest that light travelled at a finite speed. ○ Fizeau ■ Used a method similar to Galileo, but with more advanced technology ■ Fizeau passed a light through a spinning toothed- wheel, and after reflecting a light from a mirror 8km

wave was expected. Qualitatively, Maxwell’s equations summarise the interactions between electric and magnetic fields and this led to the prediction of an electromagnetic wave which can propagate through space.

Describe the production and propagation of

electromagnetic waves and relate these processes

qualitatively to the predictions made by Maxwell’s

electromagnetic theory:

• Electromagnetic Waves are transverse waves made up of perpendicularly orientated and oscillating electric and magnetic waves
• They oscillate perpendicular to the direction of propagation
• Oscillating charges produce EM waves of the same frequency as the oscillation. - v = f λ can calculate the frequency and wavelength of a wave, with the speed as 3x 8 ms -
• Maxwell’s theoretical calculations for the EM Radiation (EMR) speed closely matched the experimental values, and to such an extent that it supported the idea that light is of EMR.
• Because light is an EM wave, v = c and hence: c = f λ

• The shorter the wavelength of EMR, the more penetrative it is

Conduct investigations of historical and contemporary

methods used to determine the speed of light and its

current relationship to the measurement of time and

distance. Critical and creative thinking Information and

communication technology capability:

Conduct an investigation to examine a variety of spectra

produced by discharge tubes, reflected sunlight or

incandescent filaments:

Investigate how spectroscopy can be used to provide

information about:

> the identification of elements

• Spectroscopy investigates the spectra that is produced when matter interacts with or emits EMR
• A spectroscope can identify the chemical makeup of a visible source of light because each element has its own distinctive line spectrum of emission spectra.
• There are two types of spectra, Emission and Absorption

Light: Wave Model

Analyse the experimental evidence that supported the

models of light that were proposed by Newton and

Huygens:

Conduct investigations to analyse quantitatively the

interference of light using double slit apparatus and

diffraction gratings:

Conduct investigations to analyse qualitatively the

diffraction of light:

Conduct investigations quantitatively using the

relationship of Malus’ Law for plane polarisation of light,

to evaluate the significance of polarisation in developing a

model for light:

Light: Quantum Model

Analyse the experimental evidence gathered about black

body radiation, including Wien’s Law related to Planck’s

contribution to a changed model of light:

Investigate the evidence from photoelectric effect

investigations that demonstrated inconsistency with the

wave model for light:

Analyse the photoelectric effect as it occurs in metallic

elements by applying the law of conservation of energy

and the photon model of light: