Logo situated only on titlepage of Beamer presentation
You can use
\title[Title]{Title\\[1em]\includegraphics[width=3cm]{logo}}
it's important to use the optional argument with the title once again so the right title would be used in other parts of the document (foot/headline, for example).
Another option would be to redefine the title page
template to include the logo in the desired position:
\makeatletter
\setbeamertemplate{title page}
{
\vbox{}
\vfill
\begin{centering}
\begin{beamercolorbox}[sep=8pt,center]{title}
\usebeamerfont{title}\inserttitle\par%
\vskip0.25em%
{\usebeamercolor[fg]{titlegraphic}\inserttitlegraphic\par}
\ifx\insertsubtitle\@empty%
\else%
\vskip0.25em%
{\usebeamerfont{subtitle}\usebeamercolor[fg]{subtitle}\insertsubtitle\par}%
\fi%
\end{beamercolorbox}%
\vskip1em\par
\begin{beamercolorbox}[sep=8pt,center]{author}
\usebeamerfont{author}\insertauthor
\end{beamercolorbox}
\begin{beamercolorbox}[sep=8pt,center]{institute}
\usebeamerfont{institute}\insertinstitute
\end{beamercolorbox}
\begin{beamercolorbox}[sep=8pt,center]{date}
\usebeamerfont{date}\insertdate
\end{beamercolorbox}\vskip0.5em
\end{centering}
\vfill
}
\makeatother
and then simply use \titlegraphic
:
\titlegraphic{\includegraphics[width=3cm]{logo}}
As a logo is usually associated with an organization, I use the \institute
macro to put the logo on title frame:
\institute[short name]{\includegraphics[width=3cm]{logo}}
(short name is usually printed on every slide depending on the theme used.)
But this logo is not between title and subtitle... The default order is the following:
\documentclass{beamer}
\title{title}
\subtitle{subtitle}
\institute{institute}
\author{author}
\date{date}
\titlegraphic{titlegraphic}
\begin{document}
\begin{frame}
\maketitle
\end{frame}
\end{document}
A simple solution is this:
\title{title}
\author{authorname}
\institute{\includegraphics[scale=0.035]{logo} \\Physics Department\\ IIT Bombay}