# What Factors Affect the Distance of Strong Signals in Radar Transmission?

• ick24
In summary, constructive and destructive interference occurs when two waves of the same frequency but of different phase meet and cancel each other out, while superposition is the process of adding the waves together.
ick24

## Homework Statement

Two radar transmission towers located 6.4 km apart emit identical signals of wavelength 420
meters. A ship located at a point 30 km equidistant from the
towers experiences a strong signal from the towers. However,
as it sails parallel to the line of the towers it experiences an
alternating diminishing and re-strengthen of the signal strength.
a) Calculate the distance between the points of maximum
signal strength.
b) What would be the effect on the distance between strong
signals if:
i. The distance between the towers was decreased
ii. The ship was a greater distance away from the
towers
iii. The signals had a longer wavelength
c) Given that the wavelength of the signal emitted by the towers is 450m , then
i. What is its frequency?
ii. Name the frequency band this signal would classified as.

don't really see how this question is associated with Young's Double Slit Experiment

Welcome to Physics Forums.

ick24 said:

## Homework Statement

Two radar transmission towers located 6.4 km apart emit identical signals of wavelength 420
meters. A ship located at a point 30 km equidistant from the
towers experiences a strong signal from the towers. However,
as it sails parallel to the line of the towers it experiences an
alternating diminishing and re-strengthen of the signal strength.
a) Calculate the distance between the points of maximum
signal strength.
b) What would be the effect on the distance between strong
signals if:
i. The distance between the towers was decreased
ii. The ship was a greater distance away from the
towers
iii. The signals had a longer wavelength
c) Given that the wavelength of the signal emitted by the towers is 450m , then
i. What is its frequency?
ii. Name the frequency band this signal would classified as.don't really see how this question is associated with Young's Double Slit Experiment

The radio towers are acting like the two slits, in that they are a source of waves that can interfere. The tower separation of 6.4 km is just like the distance between the two slits in Young's experiment.

So, you can use the same equation that describes interference in Young's double slit. (You should also draw yourself a figure, if you haven't already, so that you have a clear picture of the situation.)

seriously that didn't help..but thanks

There should be a discussion, and an equation, for the double slit experiment in your textbook or lecture notes. Apply the equation that deals with the interference maximums (constructive interference, or bright fringes).

ok so i got the formula for calculating the bright fringes...i put in the variables and i get 65.6km but that still does not explain the signal strength

ick24 said:
ok so i got the formula for calculating the bright fringes...i put in the variables and i get 65.6km...
That doesn't look right, it should be something much smaller. What formula did you use exactly? Can you show your calculation?
... but that still does not explain the signal strength
Do you understand what constructive and destructive interference of two waves means? That is all that is going on here.

yes..i know that destructive interference is when a trough and a crest of 2 different met and cross out each other and constructive interference is when 2 waves forms of the same phase met and create a bigger wave

ick24 said:
yes..i know that destructive interference is when a trough and a crest of 2 different met and cross out each other and constructive interference is when 2 waves forms of the same phase met and create a bigger wave

superposition check this link out maybe it will give you a better understanding

http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=19"

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ick24 said:
ok so i got the formula for calculating the bright fringes...i put in the variables and i get 65.6km but that still does not explain the signal strength

ick24 said:
yes..i know that destructive interference is when a trough and a crest of 2 different met and cross out each other and constructive interference is when 2 waves forms of the same phase met and create a bigger wave
The signal strength is strongest where there is constructive interference, and weakest where the interference is destructive. In the figures below, S1 and S2 would be the radio tower locations, and O, P, and P1 are possible locations of the ship:

(Figures are from http://www.tutornext.com/expression-intensity-light/16035" .)

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Guys i appreciate it and all but i sill can't get this.. i understand what constructive and destructive interference is but what does it have to with the signal strength

The signal is carried by radio waves. The strength of the signal is related to the amplitude as detected at the ship's location, where the waves from the two transmitters add together to produce a signal in the ship's receiver.

The amplitude, and therefore the signal strength, is highest wherever the two waves are interfering constructively. I'm confused as to why this isn't apparent, as it is pretty straightforward stuff.

If you still don't get it, I don't think I can explain it any more plainly than what I have posted here. Sorry.

I understand what's is going on here...my problem is finding a formula to solve this..I have an exam next Monday and I need to know this...

ick24 said:
I understand what's is going on here...my problem is finding a formula to solve this..I have an exam next Monday and I need to know this...
What? Earlier you said you have a formula...
ick24 said:
ok so i got the formula for calculating the bright fringes...i put in the variables and i get 65.6km but that still does not explain the signal strength
Can you show your work? What formula did you use earlier? There is a relatively simple formula for the double slit to use here. It should be in your class lecture notes or your textbook, and it can also be found via googling.

p.s. Our forum's policy is that you need to show your work before receiving help.

i only have 2 formulas
Constructive interference: r1 - r2 = m\λ ,m = 1,2,... Destructive interference:r1 - r2 = (m + 1\2)λ ,m = 1,2,...

ick24 said:
i only have 2 formulas
Constructive interference: r1 - r2 = m\λ ,m = 1,2,...

Destructive interference:r1 - r2 = (m + 1\2)λ ,m = 1,2,...
Okay. First a couple of corrections:

1. r1 - r2 = m·λ, not m\λ

2. m can be 0, as well as 1, 2,...

So how did you come up with 65.6 km before?

Hey, I have found an image that shows the situation pretty clearly:

[PLAIN]http://www.wellesley.edu/Physics/phyllisflemingphysics/106_s_physoptics_images/figure_3.gif[/CENTER]

We know that r1 and r2 differ by λ, and there are two right triangles in the figure. The idea is to solve for y in terms of d and λ.​

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y=$$\lambda$$D/a
is that the maximum signal strength

ick24 said:
y=$$\lambda$$D/a
is that the maximum signal strength
If D is the distance from the towers to the ship, and a is the distance between the two towers, then yes.

## 1. What is the problem of interference?

The problem of interference is a phenomenon that occurs when two or more waves interact with each other, resulting in a change in the overall amplitude, frequency, or wavelength of the waves.

## 2. How does interference affect experimental results?

Interference can affect experimental results in a number of ways. It can cause distortions or changes in the data, making it difficult to accurately interpret the results. In some cases, interference can also lead to the cancellation of waves, resulting in a lack of observable effects.

## 3. What are the two types of interference?

The two types of interference are constructive interference and destructive interference. Constructive interference occurs when two waves combine to produce a larger amplitude, while destructive interference occurs when two waves cancel each other out.

## 4. How can interference be reduced in experiments?

To reduce interference in experiments, scientists can use shielding materials or physical barriers to block the interfering waves. They can also adjust the positioning and orientation of the waves to minimize their interaction with each other.

## 5. How does solving the problem of interference benefit scientific research?

Solving the problem of interference is crucial in scientific research as it allows for more accurate and reliable data collection and analysis. It also helps scientists better understand the behavior and properties of waves, leading to advancements in various fields such as physics, engineering, and telecommunications.

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