Question

The diagram shows a dish antenna which is used to receive television signals from a satellite. The antenna (signal detectors) is fixed in front of the curved dish.
(a) What is the purpose of the dish?
(b) Should it concave or convex?
(c) Where should the antenna be positioned to receive the strongest possible signals?
(d) Explain what changes you would expect in the signals if a larger dish was used.

Answer 1

Hint: A dish is used to catch the signal strongly and focus it to the antenna which receives the signal and carry it through the wire to our tv. It works in the same manner as a concave mirror. The strength of the signal depends on the size of the dish.

Complete answer:
We know that a dish antenna is made of two parts. One is a dish and the other is antenna.The dish catches the signal from the medium and focuses it to the antenna. Now, the dish is analogous to a concave mirror. When light comes parallel to the principal axis, it converges at the focus of the mirror. In the dish also, when the signal falls on to it, all the signal waves converge at the focus of the dish where the antenna is placed to receive the signal easily.

So, in the given question we can answer as follows:
(a) The dish is used to collect the signal from the medium which is coming from the satellite and focus it to the antenna.
(b) It should be concave as the concave shape focuses the signal to the antenna.
(c) The antenna should be placed at the focus of the dish since all the signal waves converge at the focus.
(d) If the dish is larger more signal waves will fall on to the dish which will result in a stronger signal received at the antenna.

Note: If the dish was convex we could not focus the signal to the dish since a convex dish will diverge all the signals from the focus. In earlier days we used to use only the antenna to receive signals, which is too weak as the antenna has to catch the passing signal directly. But now, with the use of dishes the signal is much stronger.