Extensions Page 4a

Page 4a

Introducing the Focal Point Property of Parabolas

A satellite dish is a device used to receive signals that come from very far away.
Looking back to the satellite dish, you can see some supports in front of the dish which hold an instrument (a radio receiver) at the focal point of the parabolic dish.
Recall from the Parabola Module that satellite dishes are parabolic. That is, if you were to take a cross section of a satellite dish, the resulting shape would be a parabola.
Use the following action figure and question box to explore a special property of parabolas that is very important in the construction of satellite dishes.
Click the right mouse button at any point on the interior of the parabola below. This action will drop a line onto the parabola, which will then be reflected through the focal point.

You now know that every parabola has a special fixed point through which all rays travelling toward the parabola and parallel to the axis of symmetry are reflected. This property makes this point very special. We call this point the focus or focal point of the parabola.
Looking back to the satellite dish, the focal point of the parabolic dish is located at the receiver. The receiver is located at the point where the supports of the dish meet.

You saw this picture before, on the introduction page of the Parabola Module. However, now you know something very special about this satellite dish - the receiver of the dish is located exactly at the focus.

A satellite dish is a device used to receive signals that come from very far away.
Looking back to the satellite dish, you can see some supports in front of the dish which hold an instrument (a radio receiver) at the focal point of the parabolic dish.
Recall from the Parabola Module that satellite dishes are parabolic. That is, if you were to take a cross section of a satellite dish, the resulting shape would be a parabola.
Use the following action figure and question box to explore a special property of parabolas that is very important in the construction of satellite dishes.
Click the right mouse button at any point on the interior of the parabola below. This action will drop a line onto the parabola, which will then be reflected through the focal point.

You now know that every parabola has a special fixed point through which all rays travelling toward the parabola and parallel to the axis of symmetry are reflected. This property makes this point very special. We call this point the focus or focal point of the parabola.
Looking back to the satellite dish, the focal point of the parabolic dish is located at the receiver. The receiver is located at the point where the supports of the dish meet.
You saw this picture before, on the introduction page of the Parabola Module. However, now you know something very special about this satellite dish - the receiver of the dish is located exactly at the focus.