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Unformatted text preview: Chapter 21 p. 1 CHAPTER 21 Electric Charge and Electric Field 1. The magnitude of the Coulomb force is F = kQ 1 Q 2 / r 2 = (9.0 10 9 N m 2 /C 2 )(2.50 C)(2.50 C)/(3.0 m) 2 = 6.3 10 9 N . 2. The number of electrons is N = Q /( e ) = ( 30.0 10 6 C)/( 1.60 10 19 C/electrons) = 1.88 10 14 electrons . 3. The magnitude of the Coulomb force is F = kQ 1 Q 2 / r 2 = (9.0 10 9 N m 2 /C 2 )(26)(1.60 10 19 C)(1.60 10 19 C)/(1.5 10 12 m) 2 = 2.7 10 3 N . 4. The magnitude of the Coulomb force is F = kQ 1 Q 2 / r 2 = (9.0 10 9 N m 2 /C 2 )(1.60 10 19 C)(1.60 10 19 C)/(5.0 10 15 m) 2 = 9.2 N . 5. The magnitude of the Coulomb force is F = kQ 1 Q 2 / r 2 = (9.0 10 9 N m 2 /C 2 )(25 10 6 C)(3.0 10 3 C)/(0.35 m) 2 = 5.5 10 3 N . 6. The magnitude of the Coulomb force is F = kQ 1 Q 2 / r 2 . If we divide the expressions for the two forces, we have F 2 / F 1 = ( r 1 / r 2 ) 2 ; F 2 /(4.2 10 2 N) = (8) 2 , which gives F 2 = 2.7 N . 7. The magnitude of the Coulomb force is F = kQ 1 Q 2 / r 2 . If we divide the expressions for the two forces, we have F 2 / F 1 = ( r 1 / r 2 ) 2 ; 3 = [(15.0 cm)/ r 2 ] 2 , which gives r 2 = 8.66 cm . 8. The number of excess electrons is N = Q /( e ) = ( 40 10 6 C)/( 1.60 10 19 C/electrons) = 2.5 10 14 electrons . The mass increase is ? m = Nm e = (2.5 10 14 electrons)(9.11 10 31 kg/electron) = 2.3 10 16 kg . 9. The number of molecules in 1.0 kg H 2 O is N = [(1.0 kg)(10 3 g/kg)/(18 g/mol)](6.02 10 23 molecules/mol) = 3.34 10 25 molecules. Each molecule of H 2 O contains 2(1) + 8 = 10 electrons. The charge of the electrons in 1.0 kg is q = (3.34 10 25 molecules)(10 electrons/molecule)( 1.60 10 19 C/electron) = 5.4 10 7 C . Chapter 21 p. 2 10. Using the symbols in the figure, we find the magnitudes of the three individual forces: F 12 = F 21 = kQ 1 Q 2 / r 12 2 = kQ 1 Q 2 / L 2 = (9.0 10 9 N m 2 /C 2 )(70 10 6 C)(48 10 6 C)/(0.35 m) 2 = 2.47 10 2 N. F 13 = F 31 = kQ 1 Q 3 / r 13 2 = kQ 1 Q 3 /(2 L ) 2 = (9.0 10 9 N m 2 /C 2 )(70 10 6 C)(80 10 6 C)/[2(0.35 m)] 2 = 1.03 10 2 N....
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 Spring '08
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 Physics, Charge, Force

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