You charge a capacitor and then discharges it through a resistor. You notice that, after four time constants, the voltage across the capacitor has decreased to of its value just prior to the initiation of the discharge.

Suppose a diode consists of a cylindrical cathode with a radius of 6.200×10^−2 cm , mounted coaxially within a cylindrical anode with a radius of 0.5580 cm . the potential difference between the anode and cathode is 260 v . an electron leaves the surface of the cathode with zero initial speed (v initial=0). find its speed vfinal when it strikes the anode.