P dash N junction. In the EH part of this figure there are two squares representing two pieces of semiconductor material. The two peaces are not touching. The one on the left is filled in completely with dots. The dots represent electrons that have energy levels in the conduction band. The one on the right is filled in with small circles. The circles represent holes that are available for conduction. In part b the two pieces have bin placed in contact. The line down the center represents the P dash N junction. In the square on the left two columns of dots are missing so the area near the junction is devoid of dots. In the square on the right two columns of circles nearest the junction are missing so there is a blank area near the junction. The dots and circles that are left have the same density as in the original in part EH. The circles and dots near the junction have been removed. There is also a graph in part b. The horizontal axis runs the length of the joined squares and represents distance. The vertical axis represents electrical potential. The line of the graph starts out at zero on the left and rises slowly at first then more rapidly until it reaches a peak about in the middle of the blank space to the left of the junction. Then it falls quickly passing through zero at the junction and reaches a negative peak. The peak is about in the middle of the blank space just to the right of the junction. The curve rises quickly at first toward zero but slows down as it approaches zero. It reaches zero at the right end of the combined squares. End verbal description.
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