Physics - Waves

• State what is meant by the refractive index of a material

  The ratio of speed of light in a vacuum devided by the speed of light in a material or the ratio of wavelength of light in a material
• Describe 2 differences between the spectra created by a prism and the spectra created by a grating

  A prism creates 1 spectrum, a grating creates several spectra. A prism causes blue light to be refracted the most and grating causes blue light to be refracted the least
• When white is incident on a diffraction grating, fringes are produced.When white is incident on a diffraction grating, fringes are produced.

  Describe the arrangement of the red, green and blue sections of the spectrum on a faraway screen.

  mλ=d sinθ

  so larger wavelengths are diffracted to larger angles so red is diffracted more than green, which is in turn diffracted more than blue.
• The wavelength of light incident on a grading is increase, describe what affect this has on the maximas position

  mλ=d sinθ

  So if λ increases, θ increases and the maxima will be farther apart. m and d are constant.
• The frequency of light incident on a grating is increase, describe what affect this will have on the position of the maxima

  mλ=dsinθ

  So if (f) increases, λ decreases so θ decreases and the maxima will be closer together. m and d are constant
• The distance between slits is increased, describe what affect this has on the position of the maxima

  mλ=dsinθ

  So if d increases , θ decreases and the maxima will be closer together. m and d are constant
• Describe what effect wavelength has on the amount of refraction experience

  Smaller wavelength refract more than larger wavelengths
• State what is meant by the term ‘critical angle’

  At angles below the critical angle all light is refracted

  At the critical angle, light is reflected at 90 degrees

  angles above the critical angle, all light is totally internally reflected
• Explain why total internal reflection can only occur when passing from a medium of high refractive index to a medium of lower refractive index

  When passing from a high refractive index medium to a low refractive index medium light refracts away from the normal. If the incident angle is increased the refracted angle will eventually exceed 90° and the light will totally internally reflect. When going from a low refractive index medium to a high refractive index medium light refracts towards the normal and so will never exceed the 90° needed for total internal reflection.
• State the definition of irradiance

  Power per unit area
• Describe what happens to the irradiance of a light source as the distance from it is increased

  Irradiance decreases
• Describe what is meant by coherent light

  Light where there is no phase difference