Electric Charge & Force Problems - 1 v Goodman & Zavorotniy

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1 The Atom Chapter Questions 1. Which part on an atom carries a positive charge? Which carries the negative charge? 2. How many types of electric charge are there? 3. When a neutral atom captures a free electron what is the net charge on the atom? What do we call this type of atom? 4. Eight electrons orbit an oxygen atom. How many protons are in the nucleus? 5. When we remove on electron from an atom what in the net charge on the atom? What do we call this type of atom? Charging by Rubbing 6. What happens to a plastic rod when it is rubbed with a piece of animal fur? What happens to the piece of fur? 7. How can you tell that whether two objects, after being rubbed together, have each acquired an electric charge? How will the magnitude of the charge on each compare with one another? How about the sign of the charge on each? 8. What happens with two glass rods rubbed with silk when we bring them close to each other? 9. What happens between a plastic rod rubbed with a piece of animal fur and a glass rod rubbed with a piece of silk when we bring them close to each other? 10. What happens with two plastic rods rubbed with animal fur when we bring them close to each other? 11. Repeat question #8 for a charged glass rod. Charging by Conduction & Induction, Electroscopes, Grounding : 12. Describe two ways that you can give an electroscope a positive charge? 13. A student has a charged glass rod but he wants to charge an electroscope negatively. What should he do to accomplish that? Why does that work? 14. A student brings a charged plastic rod near a tiny piece of paper that is resting on a tabletop. Will the paper be attracted or repelled? Explain why and draw a diagram. 15. Why is it that when you take off a shirt or blouse in a dark room you can see tiny sparks and hear a crackling sound? 16. A positively charged rod attracts a metal ball suspended at the end on an insulating string. Draw a diagram and explain the mechanism of attraction. Electric Charge & Force Problems - 1 v Goodman & Zavorotniy

2 17. An electroscope is charged negatively and a charged rod is brought very close to it but not touching, as a result the leaves move further. What kind of electric charge is on the rod? 18. Two light paper strips are suspended at the ends of two insulating strings. One paper strip is charged the other is not charged. Design an experiment to determine which strip is charged. 19. A student touches an electroscope with his hand at the same time he brings a positively charged rod close to the electroscope without touching. When he removes his hand first and then moves the rod away from the electroscope the leaves move apart. Why? What kind of charge is on the leaves? Electric Force 20. Will two charged objects interact on the Moon, where there is no atmosphere? 21. A negatively charged oil drop falls down on a table surface. An uncharged metal sheet is placed on the table. What kind of electric charge must we add to the sheet in order to stop the drop from falling? 22. A metal sphere is charged positively. When we increase the positive charge on the sphere does it change the number of protons? 23. Is it possible to add 0.5 of electron charge to an object? Explain. 24. When you discharge a positively charged object does it mean that the object no longer contains any electric charges? Coulomb s Law Chapter Problems 1. Two positive charges of 1 mc and 10 mc are separated by a distance of 10 m. Find the direction and the magnitude of electrostatic force between the charges. 2. A particle with a charge of +7.4 μc is separated from another charged particle with a charge of 3.6 μc by a distance of 1.4 m. Find the direction and the magnitude of electrostatic force between the particles. 3. A +1.4 nc charge exerts a repulsive force of 20 mn on a second charge which is located a distance of 2.2 m away from it. What is the charge (magnitude and sign) of the second charge? 4. Two spherical objects, whose centers are 8 cm apart, have equal negative charges and repel each other with a force of 9 mn. What is the charge on each of them? How many extra electrons are on each of them? 5. Two conducting spheres have net charges of +9 μc and -7 μc and attract each other with a force of 4 mn. The spheres are brought in a contact and then moved apart to the initial distance. What is the new force between the spheres? Is this force attractive or repulsive? 6. Two negative charges of 2.5 μc and 9 μc are separated by a distance of 25 cm. Find the direction and the magnitude of electrostatic force between the charges. Electric Charge & Force Problems - 2 v Goodman & Zavorotniy

3 7. Two charges of +2.6 μc and 5.4 μc experience an attractive force of 6.5 mn. What is separation between the charges? 8. What is the distance between two charges +7.8 μc and +9.2 μc if they exert a force of 4.5 mn on each other? 9. A 4.2 μc charge exerts an attractive force of 1.8 mn on a second charge which is a distance of 2.4 m away. What is the magnitude and sign of the second charge? 10. Two equal negative point charges repel each other with a force of 18 mn. What is the charge on each object if the distance between them is 9 cm? How many extra electrons are on each object? 11. Two charged conducting spheres have net charges of +4 μc and -8 μc and attract each other with a force of 16 mn. The spheres are brought into contact and then moved apart to the initial distance. What is the new force between the spheres? Is this force attractive or repulsive? 12. What is the ratio of the electrostatic force to the gravitational force between two electrons? General Problems -Q 13. A conducting sphere is carrying a negative charge of 6 μc and is placed on an insulated tabletop. A 0.2 g oil drop is suspended 1.5 m above the sphere. Draw a free-body diagram showing all the forces acting on the drop. b. What is the sign of the net charge of the drop? c. Determine the magnitude of the electric charge on the drop. d. If we double the charge on the drop what will be its initial acceleration? Electric Charge & Force Problems - 3 v Goodman & Zavorotniy

4 14. A 0.14 kg metal ball is suspended at the end of a string and carries a positive charge of +10 nc. A charged sphere with a negative charge of -25 μc is placed at 5 cm below the ball. Draw a free-body diagram showing all the forces acting on the ball. b. Find the tension force in the string. c. If the maximum tension force that the sting can withstand is 3 N, how much charge must be added to the ball in order to break the string? d. What will be the tension force in the string if we changed the charge on the sphere from -25 μc to +25 μc and leave the charge of the hanging ball at +10 nc? 15. Two identical balls (B and C) with a mass of 0.5 g are suspended from two strings as show above. The balls carry equal charges +10 nc each and are separated by a distance of 4 cm. Draw free-body diagram and show all forces applied to ball C. b. Find the tension force in the string BC. c. Draw free-body diagram and show all forces applied on ball B. d. Find the tension force in string AB. e. Answer questions a, b, c, d for the situation when the balls have equal but opposite charges (charge on B is positive and charge on C is negative). Electric Charge & Force Problems - 4 v Goodman & Zavorotniy

5 16. A positive charge Q 1 = 2.6 μc is located at a point X 1 = -3 m and a positive charge Q 2 = 1.4 μc is located at a point X 2 = +4 m. Draw free body diagrams for the electric force acting on Q 1 and Q 2. b. Find the magnitude the electric force between Q1 and Q2. c. Find the magnitude and direction of the electric force acting on Q1. d. Find the magnitude and direction of the electric force acting on Q **A positive charge Q 1 = 7.4 μc is located at a point X 1 = -2 m, a negative charge Q 2 = -9.7 μc is located at a point X 2 = 3 m and a positive charge Q 3 = 2.1 μc is located at a point X 3 = 9 m. Draw free body diagrams for the electric force acting on Q 1, Q 2 and Q 3. b. Find the magnitude of the force between Q 1 and Q 2. c. Find the magnitude of the force between Q 1 and Q 3. d. Find the magnitude of the force between Q 2 and Q 3. e. Find the magnitude and direction of the net electric force on charge Q 1. f. Find the magnitude and direction of the net electric force on charge Q 2. g. Find the magnitude and direction of the net electric force on charge Q **A negative charge Q 1 = -25 μc is located at a point X 1 = -2 m, a positive charge Q 2 = 15 μc is located at a point X 2 = 3 m and a positive charge Q 3 = 18 μc is located at a point X 3 = 9 m. Draw free body diagrams for the electric force acting on Q 1, Q 2 and Q 3. b. Find the magnitude of the force between Q 1 and Q 2. c. Find the magnitude of the force between Q 1 and Q 3. d. Find the magnitude of the force between Q 2 and Q 3. e. Find the magnitude and direction of the net electric force on charge Q 1. f. Find the magnitude and direction of the net electric force on charge Q 2. g. Find the magnitude and direction of the net electric force on charge Q 3. Electric Charge & Force Problems - 5 v Goodman & Zavorotniy

6 Chapter Questions 1. Proton, electron Negative, negative ion 4. 8 protons 5. Positive, positive ion 6. Plastic rod becomes negative, fur becomes positive 7. Use a metallic piece to see of it repels or attracts the object; the magnitude of the charge is the same for the two objects 8. Repulsion Answers 16. The electrons from the conductor move towards the closest side of the rod and attract to the positive rod. 17. The charge on the rod is negative since the leaves separate. 18. Bring another charged object and see how it interacts with the charged paper strips. 19. The charge in the leaves was negative since due to induction, electrons travel to the leaves to attract the positively rod. 20. Yes 21. Negative 22. No then it would become a different substance 23. No you cannot break up electrons 24. No, it just means it will become neutral 9. Attraction 10. Repulsion 11. Nothing neutral 12. Conduction & Induction 13. By conduction, the electroscope will be charged negatively 14. The positive charged rod will attract the paper since the electrons inside the paper will move towards the rod. 15. This is an example of static electricity where electrons are being moved from one clothing to another. Electric Charge & Force Problems - 6 v Goodman & Zavorotniy

7 Chapter Problems N repelling N attracting C or 7.7mC x 10-8 C, 5 x electrons x 10-5 N repelling N repelling m m x 10-7 C x 10-7 C, 7.95 x electrons N repelling 12. kq e q e : Gm e m e 2.3 x : 5.5 x x : 1 b N c. d N e. b N c N d N e N f N g N General Problems i. ii N 14. b. Negative c x 10-8 C d. 9.8 m/s 2 upward iii. iv N 16. F 21 b N c N d N e N f N g N b N c. 8.1 x 10-9 C d N b N or 669 μc c N or -669 μc d N or +669 μc Electric Charge & Force Problems - 7 v Goodman & Zavorotniy