The electric fields at point P due to the positive charges q1 and q2 are shown in Fig. Q21.22. Does the fact that they cross each other violate the statement in Section 21.6 that electric field lines never cross? Explain.

Physics 2 for Engineering Week 6 (Oct 9-15) Current = charge flow per unit time I = dQ / dt = nqAv d Where n = # of particles per unit volume; v = ddift velocity; q = charge/particle Current is a scalar quantity in C/s or Amperes Electric field means moving charges J = current density (scalar) J = I / A = nqv d Resistivity ρ = E / J ρ (T) = ρ [1 + α (T-T )] 0 0 Where ρ i0 the resistivity at reference temperature T 0 Where α is the temperature coefficient of resistivity, unit in 1 / degrees Celsius R = ρL / A = V / I R is in ohms, one ohm = 1 V / A Ohm’s Law V = IR Only for Ohmic material