Physics Common Response

Question 1

Explain the formation of interference patterns

Answer 1

• laser light made up of electromagnetic waves
• as the waves pass through mesh > diffract
• when light reaches screen > interference pattern
• when light from different waves meet the screen in phase with one another > constructive interference (resulting in maxima)
• light arrives in phase with path difference n(wavelength), where n = 1,2 etc

Question 2

Assess the evidence for Newton’s theory of light

Answer 2

• very little evidence to support
• newton’s theory state that light consists of small solid particles with intrinsic properties such as shape and sides
• could accurately predict reflection and refraction of light, and dispersion into the colours
• no empirical evidence that supported the wave model, and he was contradicted through Young’s double slit

Question 3

Assess the evidence for Huygen’s theory of light

Answer 3

• consisted of wave model of light (where wavelets propagate from individual spreading out centres along the wavefront)
• Huygen’s theory was clearly supported through empirical evidence
• Young’s double slit experiment, demonstrating diffraction and interference patterns provided strong evidence
• Foucault verified Huygen model by showing that light travels slower in denser material

Question 4

Assess Maxwell’s contribution to the classical theory of electromagnetism

Answer 4

• vitally important to classical theory (3 predictions)
• light is an em wave, with self-propagating electric and magnetic fields
• light is only one part of spectrum
• the speed of electromagnetic waves is c
• Maxwell was the foundation of electromagnetism

Question 5

Explain how the spectra of a star is produced, and how it can be used to show the star’s composition

Answer 5

• continuous spectrum is emitted from the core of the star
• travels outwards through the photosphere
• photons with energies that correspond to the atomic energy level transitions of the gases that make up the photosphere are absorbed
• photons of these energies are missing from the emission spectra of the star on earth
• each element in the star will give rise to a unique series of lines which enables elements present in the star to be determined (chem comp)
• the abundance of these elements are measured through the intensities of the spectral lines

Question 6

characteristics of stars found from its spectra

Answer 6

surface temp
- determined through Wein’s Law, where wavelength max is determined from the stars spectrum.
- longer wavelengths > cooler temp
- shorter wavelengths > warmer temp

chemical comp
- found by comparing the emission spectra of known elements, with the absorption spectra of a star
- the absorption levels ate present due to the atomic energy level transitions of the atoms in the photosphere
- shared bonds indicate the elements presence

translational velocity
- obtained through red or blue shift
- red-shifted (longer wavelength) it is moving away
- blue-shifted (shorter wavelength) it is moving towards
- the larger the shift, the faster it’s moving

rotational velocity
- determined through the width of the absorption bands
- faster it is rotating, the wider the absorption bands are

density layers
- obtained through the spectra
- wider absorption pattern for more dense (as a more dense star has more collisions)
- this is called collisional broadening

Question 7

Explain strategies to improve transformer efficiency

Answer 7

• Eddy currents (resistive heating effects)
  laminate to have smaller or prevent eddy currents
• Incomplete flux linkage between primary and secondary
  solid iron core