[Tex/LaTex] Why would I need to put a $

Question

line 41: Missing $ inserted. ... of a single electron is -1.6 $\times$ 10^
line 41: Overfull \hbox (155.52795pt too wide) in paragraph

These are the error messages that are displayed and I don't know why. What do these mean?

Answer 1

Alternative: Don't worry yourself about such things or risk running in such errors, simply let the siunitx package do it for you:

\documentclass{article}

\usepackage{siunitx}

\begin{document}

the charge of a single electron is \SI{-1.6e-19}{\coulomb} 

\end{document}

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EDIT: With this many votes, I feel this answer needs something more creative to deserve the votes. So here an example how flexible siunitx is:

\documentclass{article}

\usepackage{siunitx}
\usepackage{phaistos}
\usepackage{starfont}
\usepackage{wasysym}

\DeclareSIUnit{\water}{\text{\Aquarius}}
\DeclareSIUnit{\duck}{\text{\PHdove}}
\DeclareSIUnit{\cookie}{\text{\PHshield}}
\DeclareSIUnit{\happy}{\smiley}


\begin{document}

A duck with cookies and water is happy: 

\[
\SI{1}{\duck} + \SI{3}{\cookie} + \si{\water} = \SI[parse-numbers=false]{\infty}{\happy} 
\]

\end{document}