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The illustration shows a wire that is oriented along the z axis, carries a varying current I of t. A point Q equals (R, theta, phi) located at a distance of R from the origin in the z y plane. The distance between the point Q and another point along the dipole is R prime. An angle theta is formed between R and the z axis. The point Q is projected on the x-y plane. The distance from the projected point and the origin makes an angle phi with the x-axis.