Q. A 2.5g copper penny is given a charge of -0.50 mC.
How many excess electrons make up this charge?
What is the percentage of the mass of these excess electrons to the mass of the penny?
Q. A resistor is constructed of a carbon rod that has a uniform cross-sectional area of 5.00 mm2. When a potential difference of 15.0 V is applied across the ends of the rod, the rod carries a current of 4.00 × 10-3 A. Find (a) the resistance of the rod and (b) the rod's length.