## PHYS208 Fundamentals of Physics II

### Hint for Ch. 23, 32P

By symmetry, both +*q* and -*q* produce equal magnitude contributions to the electric field;
the horizontal components sum to zero, leaving only a net electric field downward.

### Hint for Ch. 23, 33P

Consider charge elements that are conjugate about the perpendicular bisector of P. Set origin of integration there and integrate from -L/2 to L/2.
Do not forget the trigonometric factor for projection along the "non-cancellation" direction.

### Hint for Ch. 23, 34P

Span the rod with a variable *x*.
I chose *x=0* at the end closest to P so that integration was from 0 to -L.
The contribution to the electric field from each infinitesimal element charge
points to the right. *Check the far-field limit for point-charge behavior.*

### Hint for Ch. 25, 42P

Use the same set-up of infinitesimal charge and integration variable as 23: 43P, but remember that the charge density depends on that variable.
Remember to check that the far-field limit reduces to that of the appropriate point charge.

"http://www.physics.udel.edu/~watson/phys208/exercises/hints/0225.html"

Last updated Feb. 25, 1998.

Copyright George Watson, Univ. of Delaware, 1998.