There seem to be two series of symbols for capacitors whatever their nature; one has two straight parallel lines with or without extra detail, the other, one straight line and one curved line. I can't find any suggestion for the difference but looking at many circuit diagrams in Scherz and Monk's Electronics tome I get the feeling that their is a reason but can't put my finger on it . What am I missing please ?

Ken

 

A capacitor symbol with a curved line indicates a polarized capacitor such as an electrolytic where positive and negative orientation must be followed. Two straight lines indicate non-polarized as in a ceramic capacitor

 

A capacitor symbol with a curved line indicates a polarized capacitor such as an electrolytic where positive and negative orientation must be followed. Two straight lines indicate non-polarized as in a ceramic capacitor

This is in the US and , no doubt other places that I don't know about.
In Europe and, no doubt, other places that I don't know about other symbols are used.
The image below is from https://electronics.stackexchange.c...voltage-that-looks-like-a-shaded-in-capacitor

 

Ah, thank you both. Clearly another example of being divided by a common language, Scherz is a North American while Monk lives fifty miles from me in Lancashire. The symbols presumably reflect who drew the circuit. I was beginning to think my old brain was letting me down. which in a sense it was.
Thank you for relieving me of having to cope with yet another complexity.

Ken