Now we will derive the potential of a uniformly charged disk along the axis of the disk. First consider a charge element dq on a flat circular strip of radius y and width dy. The charge in this strip will be equal to the charge per unit area multiplied by the area of the strip. The disk is uniformly charged, so the charge per unit area is constant. The symbol s is used to represent the charge per unit area of the disk. The area of the strip is given by 2p times y times dy. The potential due to the charge strip at a distance x along the axis can be found by using the potential expression previously derived. Substitute for the charge element dq that we have already found and for the distance r from the disk to the point x along the axis. Integrate over all of the charged strips from zero to a to find the potential at distance x due to the disk. To simplify the integral, cancel out like terms and move all constants in front of the integral. Perform the integral over y noticing that the x in the denominator does not depend on y. If x is much larger than a it can be shown that this expression reduces to the potential of a point charge.

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