Ch. 14 Light and Reflection

Spherical aberrations – a blurred image produced from rays that reflect at points on a mirror far from the principle axis.

Parabolic mirrors eliminate spherical abberations Are segments of a paraboloid (a three-dimensional parabola) All rays parallel to the principle axis converge at the focal point. Good for flashlights headlights

Reflecting telescopes use parabolic mirrors can reflect and focus electro- magnetic radiation of different wavelengths

Other type of telescope Refracting telescope – uses a combination of lenses to form an image

Color Objects absorb certain wavelengths from the light falling on them and reflect the rest. The color of an object depends on which wavelengths of light shine on the object and which wavelengths are reflected. Ex. Green leaves absorb all colors except green. Green is reflected and that is what we see

Additive Primary colors Red, blue, green Produce white light when combined Complementary colors are cyan, magenta, and yellow

Additive Primary colors Two primary colors combine to produce a complementary color Additive colors are used to color glass, produce images on television. The human eye has cone cells that are sensitive to red, blue and green Light of different wavelengths stimulate a combination of these receptors so a wide range of colors can be perceived.

Subtractive primary colors Cyan, magenta, and yellow Light is absorbed or subtracted from incoming light Complementary colors are red, blue, and green

Subtractive primary colors When pigments are mixed, each one subtracts certain colors from white light and the resulting color depends on the frequencies that are not absorbed.

Polarization of Light Allows some light to be filtered by certain materials Most light consists of waves that have electric fields oscillating in random directions (unpolarized) They are combinations of vertical and horizontal electric field oscillations

Light whose electric field waves are oriented in the same direction have linear polarization Light can be linearly polarized through transmission by being passed through certain transparent crystals

The light is passed through the crystal. The crystal will only allow certain parts of light to go through The light must pass through the transmission axis Any light waves that are linearly polarized with respect to the transmission line will pass through

Light can be polarized by reflection and scattering When light is reflected at a certain angle from a surface, the reflected light is completely polarized parallel to the reflecting surface