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Static, Voltage, and Capacitor Review Name:_____________ Date:______________ Short Answer and T/F: (3 pts each) 1) Name two materials that electrons are allowed to move freely on: 2) If you rub a balloon with a cloth, why does dust become attracted to it? 3) How does the charge of a proton differ from the charge of an electron? 4) Explain how an object is charged by polarization: (you may use pictures if needed) 5) Explain why the leaves of an electroscope repel when a charged source is brought near it? 6) A charge on a rod is brought near a conductor. Draw an arrow on the sphere that represents the direction the electrons are repelled. ++ ++ ++ ++ ++ __ __ __ __ __ _ 7) T/F: An object may become positively charged by electrons transferring between materials 8) T/F: Insulators confine their charges to concentrated areas, this is why a copier works. Electric Field Calculations: A) Find the electric field strength at location A (2meters from the source) if the sphere has a charge of +2C. B) Find the force on a +.5C charge that is located at location A Electric Fields: Draw both the charge and the electric field on the following objects: (3pts each) + and – plate Box is - Plate is + Voltage: (3pts each) 1) Voltage may be thought as electrical ______________________. 2) The following spheres have charges on them where the “-“ a negative charge. If a wire where connected between the following spheres state which directions the electrons will flow: Between -2C and -9C:_____________ Between -9C and -10C:_____________ -9C +2C Between -2C and +7C:____________ Between -10C and +2C:_____________ -10C +7C Capacitance: 1) What is the function of a capacitor? 2) Why does a capacitor have a material kept between them? Calculating capacitance: 1) Find the capacitance of a parallel plate capacitor that has a surface area of .008m2 and a distance between the plates that is .0003m. Find the capacitance of this capacitor. (5pts) (ans: 2.36 x 10-10 F) 2) If the capacitor above is charged a with a 7V source, find the charge stored in it. (5pts) (ans: 1.65 x 10-9 C) 3) For the same capacitor, find the PE stored in it while charged at 5V. (5pts) (ans: 2.95 x 10-9 J)