Basic Physics II Evidences - DrJJ - UiTM

Samples of conceptual and analytical/numerical questions from chap19, C&J, 7E16. REASONING The electric potential at a distance r from a point charge q is given byEquation 19.6 as V = kq/r. The total electric potential at location P due to the six pointcharges is the algebraic sum of the individual potentials.+7.0q +3.0q +5.0qddddPdd−5.0q −3.0q +7.0qSOLUTION Starting at the upper left corner of the rectangle, we proceed clockwiseand add up the six contributions to the total electric potential at P (see the drawing):V( + 7.0 ) ( + 3.0 ) ( + 5.0 ) ( + 7.0 ) ( −3.0 ) ( −5.0)k q k q k q k q k q k q= + + + + +ddd + ⎜ ⎟ 2 d + ⎜ ⎟ d + ⎜ ⎟ 2 d + ⎜ ⎟⎝ 2⎠ ⎝ 2⎠ ⎝ 2⎠ ⎝ 2⎠=k2 2 2 22 ⎛d ⎞ 2 ⎛d ⎞ 2 ⎛d ⎞ 2 ⎛d⎞( + 14.0q)d2⎛d⎞+ ⎜ ⎟⎝ 2 ⎠2Substituting q = 9.0 × 10 −6 C and d = 0.13 m gives⎛29 N⋅m ⎞6⎜8.99× 102 ⎟ + 14.0 9.0×10 Ck( + 14.0q)C6V = =⎝ ⎠= + 7.8×10 V2 22 ⎛d⎞ 2 ⎛0.13 m ⎞d + ⎜ ⎟ ( 0.13 m)+ ⎜ ⎟⎝ 2⎠ ⎝ 2 ⎠___________________________________________________________________________−( )( )37. The membrane that surrounds a certain type of living cell has a surface area ofand a thickness of. Assume that the membrane behaves like aparallel plate capacitor and has a dielectric constant of 5.0. (a) The potential on the outersurface of the membrane is +60.0 mV greater than that on the inside surface. How muchcharge resides on the outer surface? (b) If the charge in part (a) is due to K + ions (charge +e),how many such ions are present on the outer surface?37. SSM REASONING The charge that resides on the outer surface of the cellmembrane is q = CV , according to Equation 19.8. Before we can use this expression,however, we must first determine the capacitance of the membrane. If we assume thatthe cell membrane behaves like a parallel plate capacitor filled with a dielectric,Equation 19.10 (C =κ ε 0A / d ) applies as well.SOLUTION The capacitance of the cell membrane isCompiled by DrJJ Page 6 of 9 8/17/2006