Additional Exercises Electrostatics practice /6/ 27 A-1: A raindrop acquires a negative charge of 3.0 x 10 18 C as it falls. What is the force of attraction when the raindrop is 6.0 cm from the bulb on the end of a car antenna that holds a charge of 2.0 x 10-6 C? A-2: In a grain elevator on Farmer Judd's farm, pieces of grain become electrically charged while falling through the elevator. If one piece of grain is charged with 5.0 X 10 16 C while another holds 2.0 x 10-16 C of charge, what is the electrostatic force between them when they are separated by 0.050 m? A-3: Rocco, an auto body painter, applies paint to automobiles by electrically charging the car's outer surface and oppositely charging the paint particles that he sprays onto the car. This causes the paint to adhere tightly to the car's surface. If two paint particles of equal charge experience a force of 4.0 X 10- N between them at a separation of 0.020 cm, what is the charge on each? A-4: After unpacking a shipment of laboratory glasswear, Mrs. Payne dumps the box of Styrofoam packing chips into a recycling bin. The chips rub together and two chips 0.015 m apart repel each other with a force of 6.0 x 10-3 N. What is the charge on each of the chips? A-5: Wiz the cat is batting at two Ping-Pong balls hanging from insulating threads with their sides just barely touching. Each ball acquires a positive charge of 3.5 X 10 C from Wiz's fur and they swing apart. a) If a force of 6.0 X 10 N acts on one of the balls, how far apart are they from each other? b) Is the force between them one of attraction or repulsion? A-6: A droplet of ink in an ink-jet printer carrying a charge of 8.0 x 10-13 C is deflected onto the paper by a force of 3.2 x 10 4 N. How strong is the field that causes this force? A-7: In the human body, nerve cells work by pumping sodium ions out of a cell in order to maintain a potential difference across the cell wall. If a sodium ion carries a charge of 1.60 X 10 9 C as it is pumped with an electrical force of 2.0 x 10 12 N, what is the electric field between the inside and outside of the nerve cell? A-8: Each of two Van de Graaff generators, whose centers are separated from one another by 0.50 m, becomes charged after they are switched on. One Van de Graaff generator holds +3.0 x 10-2 C while the other holds -2.0 x 10-2 C. What is the magnitude and direction of the electric field halfway between them? A-9: Willa the witch dusts her crystal ball with her silk scarf, causing the ball to become charged with 5.0 x 10 9 C. Willa then stares into the crystal ball and the wart on the end of her nose experiences an electric field strength of 2200 N/C. How far is the tip of her nose from the center of the crystal ball? 206 Electrostatics