Chapter 15 Electric Forces and Electric Fields CHAPTER 15 Conceptual Questions C1 Object A has a charge q on it object B has a charge q on it and object C has a charge 2q on it These charges are arranged one each at the vertices of an equilateral triangle Which charge has the greatest magnitude electric force on it a A b B c C d All have equal magnitude forces on them C2 Three equal positive charges are placed on the x axis one at the origin one at x 2 m and the third at x 4 m Of the following points which has the greatest magnitude electric field a x 1 m b x 3 m c x 5 m d The electric field has the same magnitude at all three positions C3 Charges q q and q are placed on the x axis at x 0 x 2 m and x 4 m respectively At which of the following points does the electric field have the greatest magnitude a x 1 m b x 3 m c x 5 m d The electric field has the same magnitude at all three positions C4 Two small objects are suspended from threads When the objects are moved close together they attract one another Which of the following could produce this result a One object is positively charged and the other is negatively charge b One object is positively charged and the other is uncharged c One object is negatively charged and the other is uncharged d All of the above could result in such attraction C5 A spherical surface surrounds a point charge it its center If the charge is doubled and if the radius of the surface is also doubled what happens to the electric flux E out of the surface and the magnitude E of the electric field at the surface as a result of these doublings a E and E do not change b E increases and E remains the same c E increases and E decreases d E increases and E increases 1 Chapter 15 Electric Forces and Electric Fields 15 1 Properties of Electric Charges 1 Doug rubs a piece of fur on a hard rubber rod giving the rod a negative charge What happens a Protons are removed from the rod b Electrons are added to the rod c The fur is also charged negatively d The fur is left neutral 2 A repelling force must occur between two charged objects under which conditions a Charges are of unlike signs b Charges are of like signs c Charges are of equal magnitude d Charges are of unequal magnitude 3 When a glass rod is rubbed with silk which of the following statements best describes what happens a Electrons are removed from the rod b Protons are removed from the silk c The silk is charged positively d The silk remains neutral 4 A metallic object holds a charge of 3 8 10 6 C What total number of electrons does this represent e 1 6 10 19 C is the magnitude of the electronic charge a 4 2 1014 b 6 1 1013 c 2 4 1013 d 1 6 1014 5 When charging two objects by rubbing them together a Neither may be a conductor b They must be made of different material c They will sometimes end up with both being positively charged d The heat produced by friction is a necessary part of this process 6 About how many electrons are in 30 grams of water H2O 2 Chapter 15 Electric Forces and Electric Fields a 1025 b 1023 c 1021 d 1019 3 Chapter 15 Electric Forces and Electric Fields 7 Who was the first to determine the electron s charge a Franklin b Coulomb c Millikan d Faraday 15 2 Insulators and Conductors 8 An uncharged conductor is supported by an insulating stand I pass a positively charged rod near the left end of the conductor but do not touch it The right end of the conductor will be a negative b positive c neutral d attracted 9 Of the following substances which one contains the highest density of free electrons a hard rubber b iron c amber d glass 10 Which of the following best characterizes electrical conductors a low mass density b high tensile strength c electric charges move freely d poor heat conductors 11 Which of the following best characterizes electrical insulators a charges on the surface don t move b high tensile strength c electric charges move freely d good heat conductors 12 If body M with a positive charge is used to charge body N by induction what will be the nature of the charge left on the latter a must be equal in magnitude to that on M b must be negative 4 Chapter 15 Electric Forces and Electric Fields c must be positive d must be greater in magnitude than that on M 5 Chapter 15 Electric Forces and Electric Fields 13 If body P with a positive charge is placed in contact with body Q initially uncharged what will be the nature of the charge left on Q a must be equal in magnitude to that on P b must be negative c must be positive d must be greater in magnitude than that on P 14 I wish to use a positively charged rod to charge a ball by induction Which statement is correct a The charge on the ball will be positive b The ball must be a conductor c The ball must be an insulator that is connected temporarily to the ground d The ball is charged as the area of contact between the two increases 15 How can a charged object attract an uncharged object made of non conducting material a The uncharged object must somehow gain a like charge b The uncharged object must somehow gain an unlike charge c The charges in the uncharged object can become polarized d Attraction of an insulator is not possible 15 3 Coulomb s Law 16 Two point charges are 4 cm apart They are moved to a new separation of 2 cm By what factor does the resulting mutual force between them change a 1 2 b 2 c 1 4 d 4 17 If the distance between two point charges is tripled the mutual force between them will be changed by what factor a 9 0 b 3 0 c 0 33 d 1 9 18 If the size of the charge value is tripled for both of two point charges maintained at a constant separation the mutual force between them will be changed by what factor 6 Chapter 15 Electric Forces and Electric Fields a 9 0 b 3 0 c 0 33 d 1 9 19 The constant ke which appears in Coulomb s law formula is equivalent dimensionally to which of the following a N m C b N C c N m2 C2 d N C2 20 Two point charges separated by 1 5 cm have charge values of 2 0 and 4 0 C respectively What is the value …