What causes TV static interference meaning

Mechanical waves

The superposition of waves is called interference designated. If there are only two transmitters (sources) from which waves emanate, one speaks of two-source interference (ZQI). Examples of transmitters are two swabs in a water wave tub, two loudspeakers or two columns from which elementary waves emanate.

Assumptions

To simplify matters, we want to assume that the waves under consideration are harmonic and have the same amplitude, frequency and direction of oscillation.

Imagine a calm lake in which two swabs (transmitter S1 and S.2) and create two circular wave systems, as well as a cork (receiver E) some distance away, which is captured by the waves and excited to vibrate. When the waves are superimposed, the following two extreme cases occur:

Constructive interference

A mountain of wave 1 meets a mountain of wave 2 or a valley of wave 1 meets a valley of wave 2. In this case there is a maximum deflection (e.g. of the cork).

Constructive interference always occurs when the path difference \ (\ Delta s = \ left | {\ overline {{S_2} E} - \ overline {{S_1} E}} \ right | \) applies
\ [\ Delta s = k \ cdot \ lambda \; \; \; \ rm {with} \; \; \; k \ in \ left \ {{\ color {Red} {0} \ ;; \; 1 \ ;; \; 2 \ ;; \; ...} \ right \} \]

One speaks for \ (k = 0 \ Rightarrow \ Delta s = 0 \ cdot \ lambda = 0 \) of the maximum of 0th order.

For \ (k = 1 \ Rightarrow \ Delta s = 1 \ cdot \ lambda = \ lambda \) there is a maximum of 1st order.

Destructive interference

A mountain of wave 1 meets a valley of wave 2 or a valley of wave 1 meets a mountain of wave 2. In this case, extinction occurs (e.g. no deflection of the cork).

Destructive interference always occurs when the path difference \ (\ Delta s = \ left | {\ overline {{S_2} E} - \ overline {{S_1} E}} \ right | \) the values ​​\ (\ frac {\ lambda} {2} \), \ (3 \ cdot \ frac {\ lambda} {2} \), \ (5 \ cdot \ frac {\ lambda} {2} \) etc. Mathematically elegant, this can be written in the following form:
\ [\ Delta s = \ left ({k - \ frac {1} {2}} \ right) \ cdot \ lambda \; \; \; \ rm {with} \; \; \; k \ in \ left \ {{\ color {Red} {1} \ ;; \; 2 \ ;; \; 3 \ ;; \; ...} \ right \} \]

One speaks for \ (k = 1 \ Rightarrow \ Delta s = \ left ({1 - \ frac {1} {2}} \ right) \ cdot \ lambda = \ frac {\ lambda} {2} \) of the minimum 1st order.

Angular width \ (\ alpha \)

The calculation of the angular width \ (\ alpha \) below which a maximum or minimum appears is particularly easy if the distance \ (a \) of the receiver E is very large compared to the distance \ (b \) of the two transmitters ( \ (b \ ll a \)). In this case the lines \ (\ overline {\ rm {S_1 E}} \) and \ (\ overline {\ rm {S_2 E}} \) almost parallel and the angle \ (\ alpha \) very small.

From the drawing it can be seen that \ (\ Delta s \) applies to the path difference
\ [\ sin \ left (\ alpha \ right) = \ frac {{\ Delta s}} {b} \ Leftrightarrow \ Delta s = b \ cdot \ sin \ left (\ alpha \ right) \ quad (1) \ ]
and that \ (\ alpha \) applies to the angular width
\ [\ tan (\ alpha) = \ frac {d} {a} \ quad (2) \]
If \ (\ alpha \) is very small (i.e. in school practice \ (\ alpha <5 ^ \ circ \)), then the sine and tangent of an angle agree well, i.e. \ (\ tan (\ alpha) \ approx \ sin (\ alpha) \); this is called the Small angle approximation. With this approximation it follows from \ ((1) \) and \ ((2) \)
\ [\ Delta s = b \ cdot \ tan \ left (\ alpha \ right) = b \ cdot \ frac {d} {a} \]