Physics: Sound and Light

Things to note:

1. Determine whether a wave is undisturbed, reflected, refracted, diffracted, or dispersed.
2. Lenses and mirrors follow the three optics rules: the focal point rule, the object rule and the image rule. 
3. To solve for the Doppler Effect: when a wave source and observer move towards one another, frequency increases--add Δf to fs to get fo. When a wave source and observer move away from each other, frequency decreases--subtract Δf from fs to get fo. 

Equations: 

• v = fλ , where 'v' is velocity, 'f' is frequency, and 'λ' is wavelength
• T = 1/f , where 'T' is period 

*Sound requires a medium to travel, while light does not. The velocity of a wave is dictated by the medium through which it travels, so when a wave travels from one medium to another, its velocity changes according to the features of the new medium. Again, mechanical waves require a medium in which to travel through, while electromagnetic waves such as light are able to travel in the absence of a medium. 

Two characteristics of a given medium determine the velocity of waves traveling through it: 

1. The medium's elasticity, or resistance to change in shape
2. The medium's inertia, or resistance to change in motion 

*The velocity of sound waves in a gas is limited by the average speed of the molecules within that gas. Sound waves move more quickly through hot gases than through cold ones. 

Remember, a frequency of a wave that moves from one medium to another does not change, but the velocity does. 

*Heaver and denser media tend to slow waves down, while "stiffer" media tend to speed waves up, because they have greater elasticity, which is caused by increasing intermolecular forces, which consequently move the waves along. 

In general: 

'v' of sound in solid > 'v' of sound in liquid > 'v' of sound in gas