Third Doctor Smooching. It's About Electronics.

A very cute short film featuring Jon Pertwee doing his best impression of Danny Kaye. He explains electronics without ever once reversing the polarity of the neutron flow!  If nothing else, this film has a shot of Pertwee passionately kissing a cute girl -- something his Doctor never got to do.  The world would have to wait for David Tennant before we'd have that sort of thing going on.