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Unformatted text preview: 26.16. Model: Charges A, B, and C are point charges. Visualize: Please refer to Figure EX26.16. Charge A experiences an electric force B on A F r due to charge B and an electric force C on A F r due to charge C. The force B on A F r is directed to the right and the force C on A F r is directed to the left. Solve: Coulombs law yields: ( 29 ( 29 ( 29 ( 29 9 2 2 9 9 5 B on A 2 2 9.0 10 N m /C 1.0 10 C 1.0 10 C 9.0 10 N 1.0 10 m F = = ( 29 ( 29 ( 29 ( 29 9 2 2 9 9 5 C on A 2 2 9.0 10 N m /C 1.0 10 C 4.0 10 C 9.0 10 N 2.0 10 m F = = The net force on A is ( 29 ( 29 ( 29 5 5 on A B on A C on A 9.0 10 N 9.0 10 N 0 N F F F i i = + = +  = r r r 26.18. Model: Objects A and B are point charges. Visualize: Because there are only two charges A and B, the force on charge A is due to charge B only, and the force on B is due to charge A only. Solve: Coulombs law gives the magnitude of the forces between the charge. Thus, F A on B = F B on A = 9.0 10 9 N m 2 /C 2 ( 29 20.0 10 9 C ( 29 10.0 10 9 C ( 29 2.0 10 2 m ( 29 2 = 4.5 10 3 N Because the charge on object A is positive and on object B is negative, F B on A is upward and F A on B is downward. Thus, r F B on A = + 4.5 10 3 j N r F A on B =  4.5 10 3 j N 26.26. Model: A field is the agent that exerts an electric force on a charge. Visualize: Solve: (a) To balance the gravitational force on a proton ( 29 ( 29 net on p p G y F F F = = r r N. This means ( 29 ( 29 ( 29 27 7 on p 19 p 1.67 10 kg 9.8 N/kg 1.02 10 N/C 1.60 10 C G mg F F q E mg E q = = = = = Because F on p must be upward and the proton charge is positive, the electric field at the location of the proton must also be pointing upward. Thus ( 29 7 1.02 10 N/C, downward . E = r (b) In the case of the electron, ( 29 ( 29 31 11 19 9.11 10 kg 9.8 N/kg 5.58 10 N/C 1.60 10 C mg E q = = = Because F on e must be upward and the electron has a negative charge, the electric field at the location of the electron must be pointing downward. Thus electron must be pointing downward....
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This note was uploaded on 04/03/2012 for the course PHYSICS AN 101 taught by Professor N.a during the Spring '12 term at Clark College.
 Spring '12
 n.a

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