Little Johnny was eating breakfast one morning and got to thinking about things. “Mommy, mommy, why has daddy got so few hairs on his head?” he asked his mother.
“He thinks a lot,” replied his mother, pleased with herself for coming up with a good answer to her husband's baldness.
Or she was until Johnny thought for a second and asked, “So why do you have so much hair?”
Crystal rectifierIn 1874, a paper by Ferdinand Braun (1850-1918) was published in the Annalen der Physik und Chemie describing his discovery of the electrical rectifier effect. He observed that certain crystals of metal sulphides have a larger or smaller resistance to an electric current, depending on its direction of flow. He used a galena crystal, a semiconductor material composed of lead sulfide. He found the rectifying effect especially true if at least one of the electrodes was a pointed wire. Thus, he had discovered the point-contact rectifier effect, the first semiconductor device. This effect wasn't used until over 30 years later in the form of the “cat's whisker”crystal radio detector which ultimately led to the point-contact transistor first produced in 1948. |
