1. Light & The Wave Speed Equation Using the wave speed equation to solve problems about electromagnetic waves

2. Wave speed tells you how fast a wave is moving Wave speed is measured in units meters per second (m/s) Wave Speed

3. The Wave Speed Equation v – wave speed (m/s) λ – wavelength (m) f – frequency (Hz) v = λf (Wave speed = wavelength times frequency) When solving problems about EM waves, the wave speed is always equal to the speed of light: v = c = 3 x 10 8 m/s

4. The Wave Speed Equation Practice: Red visible light has a wavelength of 6.5x10 -7 m. What is the frequency of red light? Solution: G (givens): λ = 6.5 x 10 -7 m v=c=3x10 8 m/s U (unknown): f = ? E (equation): v = λf S (substitute): 3 x 10 8 m/s = 6.5 x 10 -7 m × f S (solve):  see next slide Given in the problem. Not given in the problem. This is the speed of light, which is the value you use for ALL electromagnetic waves.

5. The Wave Speed Equation Practice: Red visible light has a wavelength of 6.5x10 -7 m. What is the frequency of red light? Solution: S (substitute): 3 x 10 8 m/s = 6.5 x 10 -7 m × f S (solve): 3 x 10 8 m/s = 6.5 x 10 -7 m × f 6.5 x 10 -7 Hz 6.5 x 10 -7 m 3 x 10 8 m/s = f 6.5 x 10 -7 Hz f = 0.462 x 10 15 Hz = 4.62 x 10 14 Hz Divide both sides by 6.5x10 -7 m to cancel out this number on the right-hand side and get the frequency (f) on its own. On the left-hand side, group together your numbers and powers of ten. Simplify each group separately. When you divide powers of ten, you SUBTRACT their exponents. Write your final answer in correct scientific notation.