# Physics diffraction confused

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#1
this is what my textbook says about diffraction in TV dishes:
the bigger the dish, the stronger the signal it can receive, cuz more radio waves are reflected by the dish onto the Ariel. BUT a bigger dish reflects the radio waves to a smaller focus cuz it diffracts the waves less. The dish, therefore, needs to be aligned more carefully than a smaller dish, otherwise it will not focus the radio waves onto the ariel.

i don't understand how a bigger dish refracts the waves less? and how this means that it diffracts to a smaller focus? please could someone explain this
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2 months ago
#2
(Original post by vix.xvi)
this is what my textbook says about diffraction in TV dishes:
the bigger the dish, the stronger the signal it can receive, cuz more radio waves are reflected by the dish onto the Ariel. BUT a bigger dish reflects the radio waves to a smaller focus cuz it diffracts the waves less. The dish, therefore, needs to be aligned more carefully than a smaller dish, otherwise it will not focus the radio waves onto the ariel.

i don't understand how a bigger dish refracts the waves less? and how this means that it diffracts to a smaller focus? please could someone explain this
Hi, I don't know what you've learnt up to in class but you can link this to diffraction through single/double slits. Its a similar concept I think. A bigger dish refracts the waves less just like a wider slit will diffract the waves less. When I was taught this I found it helpful to think about how a bigger slit/dish means its easier for the wave to get through so less diffraction will occur. In terms of the smaller focus, as the wave is now diffracted less its more intense/ less spread out and therefore is needs to be adjusted more carefully.
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#3
(Original post by lucy131213)
Hi, I don't know what you've learnt up to in class but you can link this to diffraction through single/double slits. Its a similar concept I think. A bigger dish refracts the waves less just like a wider slit will diffract the waves less. When I was taught this I found it helpful to think about how a bigger slit/dish means its easier for the wave to get through so less diffraction will occur. In terms of the smaller focus, as the wave is now diffracted less its more intense/ less spread out and therefore is needs to be adjusted more carefully.
oooooh
makes sense now, tysm
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