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Notes and Hints for AP Physics Summer Assignment (Note: This is not a complete guide… you will need to use other online resources to find more information on some of these topics) In Honors, we discussed REFLECTION and the mirror equations (including ray diagrams). We also discussed REFRACTION and Snell’s Law, but we didn’t discuss lenses. Some of these notes will be review, but a lot of this is new. Refraction (review) Remember that REFRACTION is the bending of light as it travels from one medium to another. Every material that light can travel through has a property called the INDEX OF REFRACTION (n). This property compares the speed of light in the material to the speed of light in a vacuum. The equation for index of refraction is as follows: n=c/v index of refraction = speed of light in vacuum / speed of light in medium *Because n is a ratio of velocities, it has NO UNITS. *Because the speed of light in a vacuum is the maximum, n CAN NEVER be less than 1 *Remember that the speed of light in a vacuum is 3.00 x 108 m/s Total Internal Reflection (NEW) When light moves from a slower medium to a faster medium, a phenomenon called TOTAL INTERNAL REFLECTION can occur. This is the phenomenon that causes you to see a reflection in the surface of the water while you are underwater. Total internal reflection occurs when the angle of incidence is greater than the CRITICAL ANGLE. The CRITICAL ANGLE changes based on the materials involved, but it is generally a large angle with respect to the normal and a small angle with respect to the boundary. It can be calculated as follows: Sin θc = n2/n1 (n1 MUST BE greater than n2 for this to apply) Sine of critical angle = index of medium 2 / index of medium 1 *If angle of incidence is GREATER THAN the critical angle, total internal reflection WILL OCCUR Lenses (NEW) LENSES are pieces of glass, plastic or another transparent material that are designed to bend light. There are 2 types of lenses: *A convex lens is called a CONVERGING lens because it causes light rays to come together (converge) *A concave lens is called a DIVERGING lens because it causes light rays to spread apart (diverge) The LENS EQUATION is identical to the mirror equation that we covered in Honors, and the MAGNIFICATION EQUATION is the same as well. The SIGNS ARE DIFFERENT, and they are listed below the equations: 1/p + 1/q = 1/f 1/object distance + 1/image distance = 1/focal length M = -q/p Magnification = -image distance / object distance SIGNS FOR LENSES: *Object distance (p) is POSITIVE in front of the lens and NEGATIVE behind the lens (generally object distance is always positive) *Image distance (q) is POSITIVE behind the lens and NEGATIVE in front of the lens *Focal length (f) is POSITIVE for a converging lens and NEGATIVE for a diverging lens The IMAGE HEIGHT equation is also the same as the one for mirrors. Remember that this is used to figure out how large the image will appear to be. M = h’ / h Where h’ is the IMAGE height and h is the OBJECT height. Lenses produce a REAL image if the image is on the OPPOSITE side of the lens from the object (q is positive). The image is VIRTUAL if it is on the SAME side of the lens as the object (q is negative). The general idea is that any image that could be projected on a screen is REAL.