Physics Diagram Drawing Software
In the past I have used xfig for such projects. Dispite the interface being very outdated (and the requirement for a three button mouse), the figures it generates are of high quality.
You can install it using sudo apt-get install xfig Recently I have started to use Inkscape for figure generation. The program can import/export from/to eps, pdf, svg, and even Latex (through PSTricks). For drawing circuit diagrams you could import existing SVG graphics of the various components as there are plenty out there on the internet (i.e. Drawing a converging lens diagram like you have above should be fairly easy. Sudo apt-get install inkscape Please beware that the learning curve for inkscape is steep. The on how to use the program is good and there are several video tutorials on how to do complex tasks already on YouTube (although frequently for graphical design, rather than technical figures) to help you learn.

Physics Diagram Software
Edit: I just read a that suggests Inkscape isn't the best for such drawings. Instead they suggest for the technical portion and Inkscape to add extra features to your graphics.

ConceptDraw DIAGRAM diagramming and vector drawing software extended with Physics solution from the Science and Education area is the best for creating: physics diagrams, pictures which describe various physical facts and experiments, illustrations of various electrical, mechanical and optic processes, of any complexity quick and easy.
- Dec 9, 2012 - The program can import/export from/to eps, pdf, svg, and even Latex (through PSTricks). For drawing circuit diagrams you could import existing SVG graphics of the various components as there are plenty out there on the internet (i.e. Drawing a converging lens diagram like you have above should.
- ConceptDraw DIAGRAM diagramming and vector drawing software extended with Physics solution from the Science and Education area is the best for creating: physics diagrams, pictures which describe various physical facts and experiments, illustrations of various electrical, mechanical and optic processes, of any complexity quick and easy.