# Homework Help: Physics in TV's

1. Mar 10, 2010

### Astar

1. The problem statement, all variables and given/known data

I was given these two questions to answer regarding TV:
1) Explain why there is a need for two sound carrier frequencies.
2)Explain why you still get good sound quality reception during a thunderstorm but picture quality declines.

2. Relevant equations
I was given this information within the question

Vision Carrier - 1.25 MHz above lower edge of channel
Vision Modulation - negative AM
Lines per picture - 625 interlaced 2:1
Line freqeuncy - 15625 Hz
Primary Sound Carrier - 5.5MHz above vision carrier
Secondary sound carrier - 242.1875kHz above primary sound carrier
sound modulation - FM

3. The attempt at a solution

1) The only thing I can think is so two sound waves can be played at the one time. For example: like having a person speaking with background music playing also.

2)I think it has something to do with picture being AM and sound being FM. I know that AM modulation is susceptible to noise. FM has less noise as a limiting circuit keepts the amplitude a near constant. The noise could explain the decline in sound quality reception...

I'm pretty stuck here. Any help would be greatly appreciated.