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13. [12] The distance between two square plates of a T T T T parallel plate capacitor with sides of length 0.70 m is d = 4 cm. The plates are charged with a V=20.0 V battery, making the top plate positive and the bottom plate negative. A proton with mass mp is accelerated from rest through a Vo =10 V potential difference and is then projected horizontally half way between the parallel plates. The charge is undeflected because of the presence of a magnetic field. (a) [3] Find the velocity of the charged particle just before is enters the parallel plates. (b) [3] Find the magnitude of the electric field. (c) [3] Find the magnitude and direction of the magnetic field between the plates which leads to the proton not being deflected by the joint action of the electric and magnetic fields. (d) [3] The voltage across the plates is now turned to zero by removing the battery and shorting the plates, while the magnetic field remains in place, Find the force (magnitude and direction) on the proton as it enters the region between the plates in which there is a magnetic field