15-1 Refraction

 The bending of a light as it passes at an angle from one medium to another.  Refraction occurs when light changes velocity. Figure 15-1 The flower looks small when viewed through the water droplet because the light from the flower is bent as it passes through the water.

 The speed of light is different depending on the medium it travels through.  When light moves from higher to lower speed, the ray is bent toward the normal. (a) When the light ray moves from air into glass, its path is bent toward the normal.

 When light moves from lower to higher speed the ray is bent away from the normal. (b) whereas the path of the light ray moving from glass into air is bent away from the normal.

 The index of refraction is the ratio of the speed of light in a vacuum to its speed in a medium.  This value is unitless and is always greater than 1.

Figure 15-5 (a)To the cat on the pier, the fish looks closer to the surface than it really is. (b)To the fish, the cat seems to be farther from the surface than it actually is.

 To find the angle of refraction we use Snell’s Law equation:

Thin Lenses

 A lens is a transparent object that refracts light by either converging or diverging to create an image.  Curved surfaces change the direction of light from point to point. The human eye acts as a type of lens converging light toward the light- sensitive retina at the back of the eyeball.

CONVERGINGDIVERGING When rays of light pass through (a) a converging lens (thicker at the middle), they are bent inward. When they pass through (b) a diverging lens (thicker at the edge), they are bent outward.

 Converging Lens: Can produce real or virtual images  Diverging Lens: Produces only virtual images  Real Images can be projected on a screen; virtual cannot.

When M is + image is real and upright. When M is – image is real and inverted.

 Sample 15B pg. 575