Ahmad uses the set-up shown below to take photographs of bird automatically. The contacts, X and Y, are...

19) Ahmad uses the set-up shown below to take photographs of bird automatically. The contacts, X and Y, are connected to a special camera by wires so that when X touches Y, the camera will take a photograph of the object at P.
(a) Explain how this set-up enables the camera to take photograph of a bird when it lands on P to eat the seeds.
(b) State a property of the material used to make Contacts X and Y.