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\begin{document}

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\begin{multicols}{3}

% +++++++++++++++++++++++

{\huge Physics}\hfill Andrew Lorimer\hspace{2em}

% +++++++++++++++++++++++
\section{Motion}

  $\operatorname{m/s} \times 3.6 = \operatorname{km/h}$

  \subsection*{Inclined planes}
    $F = m g \sin\theta F_{frict} = m a$

% -----------------------
  \subsection*{Banked tracks}

    \includegraphics[height=4cm]{graphics/banked-track.png}

    $$\theta = \tan^{-1} {{v^2} \over rg}$$

    $\Sigma F$ always acts towards centre, but not necessarily horizontally

    $\Sigma F = F_{\operatorname{norm}} + F_{\operatorname{g}}={{mv^2} \over r} = mg \tan \theta$

    Design speed $v = \sqrt{gr\tan\theta}$

% -----------------------
  \subsection*{Work and energy}

    $W=Fx=\Delta \Sigma E$ (work)

    $E_K = {1 \over 2}mv^2$ (kinetic)

    $E_G = mgh$ (potential)

    $\Sigma E = {1 \over 2} mv^2 + mgh$ (energy transfer)

% -----------------------
  \subsection*{Horizontal circular motion}

    $v = {{2 \pi r} \over T}$

    $f = {1 \over T}, \quad T = {1 \over f}$

    $a_{centrip} = {v^2 \over r} = {{4 \pi^2 r} \over T^2}$

    $\Sigma F, a$ towards centre, $v$ tangential

    $F_{centrip} = {{mv^2} \over r} = {{4 \pi^2 rm} \over T^2}$

    \includegraphics[height=4cm]{graphics/circ-forces.png}

% -----------------------
  \subsection*{Vertical circular motion}

    $T =$ tension, e.g. circular pendulum

    $T+mg = {{mv^2}\over r}$ at highest point

    $T-mg = {{mv^2} \over r}$ at lowest point

% -----------------------
  \subsection*{Projectile motion}
    \begin{itemize}
      \item{horizontal component of velocity is constant if no air resistance}
      \item{vertical component affected by gravity: $a_y = -g$}
    \end{itemize}

    \begin{align*}
      v=\sqrt{v^2_x + v^2_y} \tag{vectors} \\
      h={{u^2\sin \theta ^2}\over 2g} \tag{max height}\\
      x=ut\cos\theta \tag{$\Delta x$ at $t$} \\
      y=ut \sin \theta-{1 \over 2}gt^2 \tag{height at $t$} \\
      t={{2u\sin\theta}\over g} \tag{time of flight}\\
      d={v^2 \over g}\sin \theta \tag{horiz. range} \\
    \end{align*}

    \includegraphics[height=3.2cm]{graphics/projectile-motion.png}

% -----------------------
  \subsection*{Pulley-mass system}

    $a = {{m_2g} \over {m_1 + m_2}}$ where $m_2$ is suspended

    $\Sigma F = m_2g-m_1g=\Sigma ma$ (solve)

% -----------------------
  \subsection*{Graphs}
    \begin{itemize}
      \item{Force-time: $A=\Delta \rho$}
      \item{Force-disp: $A=W$}
      \item{Force-ext: $m=k,\quad A=E_{spr}$}
      \item{Force-dist: $A=\Delta \operatorname{gpe}$}
      \item{Field-dist: $A=\Delta \operatorname{gpe} / \operatorname{kg}$}
    \end{itemize}

% -----------------------
  \subsection*{Hooke's law}

  $F=-kx$

  $E_{elastic} = {1 \over 2}kx^2$

% -----------------------
  \subsection*{Motion equations}

    \begin{tabular}{ l r }
      $v=u+at$ & $x$ \\
      $x = {1 \over 2}(v+u)t$ & $a$ \\
      $x=ut+{1 \over 2}at^2$ & $v$ \\
      $x=vt-{1 \over 2}at^2$ & $u$ \\
      $v^2=u^2+2ax$ & $t$ \\
    \end{tabular}

% -----------------------
  \subsection*{Momentum}

    $\rho = mv$

    $\operatorname{impulse} = \Delta \rho, \quad F \Delta t = m \Delta v$

    $\Sigma mv_0=\Sigma mv_1$ (conservation)

    $\Sigma E_{K \operatorname{before}} = \Sigma E_{K \operatorname{after}}$ if elastic

    $n$-body collisions: $\rho$ of each body is independent

% ++++++++++++++++++++++
\section{Relativity}

  \subsection*{Postulates}
    1. Laws of physics are constant in all intertial reference frames

    2. Speed of light $c$ is the same to all observers (Michelson-Morley)

    $\therefore , t$ must dilate as speed changes

    {\bf Inertial reference frame} $a=0$

    {\bf Proper time $t_0$ $\vert$ length $l_0$} measured by observer in same frame as events

% -----------------------
  \subsection*{Lorentz factor}

    $$\gamma = {1 \over {\sqrt{1-{v^2 \over c^2}}}}$$

    $t=t_0 \gamma$ ($t$ longer in moving frame)

    $l={l_0 \over \gamma}$ ($l$ contracts $\parallel v$: shorter in moving frame)

    $m=m_0 \gamma$ (mass dilation)

    $$v = c\sqrt{1-{1 \over \gamma^2}}$$

% -----------------------
  \subsection*{Energy and work}

    $E_0 = mc^2$ (rest)

    $E_{total} = E_K + E_{rest} = \gamma mc^2$

    $E_K = (\gamma 1)mc^2$

    $W = \Delta E = \Delta mc^2$

% -----------------------
  \subsection*{Relativistic momentum}

    $$\rho = {mv \over \sqrt{1-{v^2 \over c^2}}}= {\gamma mv} = {\gamma \rho_0}$$

    $\rho \rightarrow \infty$ as $v \rightarrow c$

    $v=c$ is impossible (requires $E=\infty$)

    $$v={\rho \over {m\sqrt{1+{p^2 \over {m^2 c^2}}}}}$$

% -----------------------
  \subsection*{High-altitude muons}
    \begin{itemize}
      {\item $t$ dilation more muons reach Earth than expected}
      {\item normal half-life $2.2 \operatorname{\mu s}$ in stationary frame, $> 2.2 \operatorname{\mu s}$ observed from Earth}
    \end{itemize}

% +++++++++++++++++++++++
\section{Fields and power}

  \subsection*{Non-contact forces}
    \begin{itemize}
      {\item electric fields (dipoles \& monopoles)}
      {\item magnetic fields (dipoles only)}
      {\item gravitational fields (monopoles only)}
    \end{itemize}

    \vspace{1em}

    \begin{itemize}
      \item monopoles: lines towards centre
      \item dipoles: field lines $+ \rightarrow -$ or $\operatorname{N} \rightarrow \operatorname{S}$ (or perpendicular to wire)
      \item closer field lines means larger force
      \item dot: out of page, cross: into page
      \item +ve corresponds to N pole
    \end{itemize}

    \includegraphics[height=2cm]{graphics/field-lines.png}

% -----------------------
  \subsection*{Gravity}

    \[F_g=G{{m_1m_2}\over r^2}\tag{grav. force}\]
    \[g={F_g \over m_2}=G{m_{1} \over r^2}\tag{field of $m_1$}\]
    \[E_g = mg \Delta h\tag{gpe}\]
    \[W = \Delta E_g = Fx\tag{work}\]
    \[w=m(g-a) \tag{app. weight}\]

    % \columnbreak

% -----------------------
  \subsection*{Satellites}

    \[v=\sqrt{Gm_{\operatorname{planet}} \over r} = \sqrt{gr} = {{2 \pi r} \over T}\]

    \[T={\sqrt{4 \pi^2 r^2} \over {GM}}\tag{period}\]

    \[\sqrt[3]{{GMT^2}\over{4\pi^2}}\tag{radius}\]

% -----------------------
  \subsection*{Magnetic fields}
    \begin{itemize}
      \item field strength $B$ measured in tesla
      \item magnetic flux $\Phi$ measured in weber
      \item charge $q$ measured in coulombs
      \item emf $\mathcal{E}$ measured in volts
    \end{itemize}

    % \[{E_1 \over E_2}={r_1 \over r_2}^2\]

    \[F=qvB\tag{$F$ on moving $q$}\]
    \[F=IlB\tag{$F$ of $B$ on $I$}\]
    \[r={mv \over qB} \tag{radius of $q$ in $B$}\]

    if $B {\not \perp} A, \Phi \rightarrow 0$ \hspace{1em}, \hspace{1em} if $B \parallel A, \Phi = 0$

% -----------------------
  \subsection*{Electric fields}

    \[F=qE \tag{$E$ = strength} \]
    \[F=k{{q_1q_2}\over r^2}\tag{force between $q_{1,2}$} \]
    \[E=k{q \over r^2} \tag{field on point charge} \]
    \[E={V \over d} \tag{field between plates}\]
    \[F=BInl \tag{force on a coil} \]
    \[\Phi = B_{\perp}A\tag{magnetic flux} \]
    \[\mathcal{E} = -N{{\Delta \Phi}\over{\Delta t}} \tag{induced emf} \]
    \[{V_p \over V_s}={N_p \over N_s}={I_s \over I_p} \tag{xfmr coil ratios} \]

    \textbf{Lenz's law:}  $I_{\operatorname{emf}}$ opposes $\Delta \Phi$

    \textbf{Eddy currents:} counter movement within a field

    \textbf{Right hand grip:} thumb points to $I$ (single wire) or N (solenoid / coil)

    \textbf{Right hand slap:} $B \perp I \perp F$

    \textbf{Flux-time graphs:} $m \times n = \operatorname{emf}$

    \textbf{Transformers:} core strengthens \& focuses $\Phi$

% -----------------------
  \subsection*{Particle acceleration}

    $1 \operatorname{eV} = 1.6 \times 10^{-19} \operatorname{J}$

    eaccelerated with $x$ V is given $x$ eV

    \[W={1\over2}mv^2=qV \tag{field or points}\]
    \[v=\sqrt{{2qV} \over {m}}\tag{velocity of particle}\]


% -----------------------
  \subsection*{Power transmission}

    % \begin{align*}
      $$V_{\operatorname{rms}}={V_{\operatorname{p\rightarrow p}}\over \sqrt{2}}$$
      P_{\operatorname{loss}} = \Delta V I = I^2 R = {{\Delta V^2} \over R} \\
      V_{\operatorname{loss}}=IR
    % \end{align*}

    Use high-$V$ side for correct $|V_{drop}|$

    \begin{itemize}
      {\item Parallel $V$ is constant}
      {\item Series $V$ shared within branch}
    \end{itemize}

    \includegraphics[height=4cm]{graphics/ac-generator.png}

% -----------------------
  \subsection*{Motors}
% \begin{wrapfigure}{r}{-0.1\textwidth}

    \includegraphics[height=4cm]{graphics/dc-motor-2.png}
      \includegraphics[height=3cm]{graphics/ac-motor.png} \\
% \end{wrapfigure}
    \textbf{DC:} split ring (two halves)

% \begin{wrapfigure}{r}{0.3\textwidth}

% \end{wrapfigure}
    \textbf{AC:} slip ring (separate rings with constant contact)

% +++++++++++++++++++++++
\section{Waves}

  \textbf{nodes:} fixed on graph

  \textbf{Longitudinal (motion $||$ wave)}
  \includegraphics[height=4cm]{graphics/longitudinal-waves.png}

  \textbf{Transverse (motion $\perp$ wave)}
  \includegraphics[height=4cm]{graphics/transverse-waves.png}

  % -----------------------
  \subsection*{Motors}
  $T={1 \over f}\quad$(period: time for one cycle)
  $v=f \lambda \quad$(speed: displacement per second)

  % -----------------------
  \subsection*{Doppler effect}
  When $P_1$ approaches $P_2$, each wave $w_n$ has slightly less distance to travel than $w_{n-1}$. Hence, $w_n$ reaches the observer sooner than $w_{n-1}$, increasing "apparent" wavelength.

  % -----------------------
  \subsection*{Interference}
  When a medium changes character, energy is reflected, absorbed, and transmitted

  % -----------------------
  \subsection*{Polarisation}
  \includegraphics[height=4cm]{graphics/polarisation.png}

  % -----------------------
  \subsection*{Refraction}
  \includegraphics[height=4cm]{graphics/refraction.png}

  Angle of incidence $\theta_i =$ angle of reflection $\theta_r$

  Critical angle $\theta_c = \sin^-1{n_2 \over n_1}$

  Snell's law $n_1 \sin \theta_1=n_2 \sin \theta_2$

% +++++++++++++++++++++++
\section{Light and Matter}

  % -----------------------
  \subsection*{Planck's equation}

  f={c \over \lambda},\quad E=hf={hc \over \lambda}=\rho c

  h=6.63 \times 10^{-34}\operatorname{J s}=4.14 \times 10^{-15} \operatorname{eV s}

  1 \operatorname{eV} = 1.6 \times 10^{-19} \operatorname{J}

  \subsection*{Force of electrons}
  F={2P_{\text{in}}\over c}

  \text{photons per second}={\text{total energy} \over \text{energy per photon}}={{P_{\text{in}} \lambda} \over hc}={P_{\text{in}} \over hf}

  \subsection*{Photoelectric effect}

  \begin{itemize}
    \item $V_{\operatorname{supply}}$ does not affect photocurrent
    \item $V_{\operatorname{sup}} > 0$: eattracted to collector anode
    \item $V_{\operatorname{sup}} < 0$: attracted to illuminated cathode, $I\rightarrow 0$
    \item $v$ of edepends on ionisation energy (shell)
    \item max current depends on intensity
  \end{itemize}

  \textbf{Threshold frequency $f_0$}

  Minimum $f$ for photoelectrons to be ejected. $x$-intercept of frequency vs $E_K$ graph. if $f < f_0$, no photoelectrons are detected.

  \textbf{Work function $\phi$}

  Minimum $E$ required to release photoelectrons. Magnitude of $y$-intercept of frequency vs $E_K$ graph. $\phi$ is determined by strength of bonding.

   $\phi=hf_0$

  \textbf{Kinetic energy}

  E_{\operatorname{k-max}}=hf - \phi

  voltage in circuit or stopping voltage = max $E_K$ in eV
  equal to $x$-intercept of volts vs current graph (in eV)

  \textbf{Stopping potential $V$ for min $I$}

  $V=h_{\text{eV}}(f-f_0)$

  \subsection*{De Broglie's theory}

  $\lambda = {h \over \rho} = {h \over mv}$
  $\rho = {hf \over c} = {h \over \lambda} = mv, \quad E = \rho c$
  \begin{itemize}
    \item cannot confirm with double-slit (slit $< r_{\operatorname{proton}}$)
    \item confirmed by similar e- and x-ray diff patterns
  \end{itemize}

  \subsection*{X-ray electron interaction}

  \begin{itemize}
    \item e- is only stable if $mvr = n{h \over 2\pi}$ where $n \in \mathbb{Z}$
    \item rearranging this, $2\pi r = n{h \over mv} = n \lambda$ (circumference)
    \item if $2\pi r \ne n{h \over mv}$, no standing wave
    \item if e- = x-ray diff patterns, $E_{\text{e-}}={\rho^2 \over 2m}={({h \over \lambda})^2 \div 2m}$
    \item calculating $h$: $\lambda = {h \over \rho}$
  \end{itemize}

  \subsection*{Spectral analysis}

  \begin{itemize}
    $n\item $\Delta E = hf = {hc \over \lambda}$ between ground / excited state
    $n\item $E$ and $f$ of photon: $E_2 - E_1 = hf = {hc \over \lambda}$
    $n\item Ionisation energy - min $E$ required to remove e-
    $n\item EMR is absorbed/emitted when $E_{\operatorname{K-in}}=\Delta E_{\operatorname{shells}}$ (i.e. $\lambda = {hc \over \Delta E_{\operatorname{shells}}}$)
  \end{itemize}

  \subsection{Indeterminancy principle}

  measuring location of an e- requires hitting it with a photon, but this causes $\rho$ to be transferred to electron, moving it.

  \subsection{Wave-particle duaity}

  wave model:

  \item cannot explain photoelectric effect
  \item $f$ is irrelevant to photocurrent
  \item predicts delay between incidence and ejection
  \item speed depends on medium

  particle model:

  \item explains photoelectric effect
  \item rate of photoelectron release $\propto$ intensity
  \item no time delay - one photon releases one electron
  \item double slit: photons interact. interference pattern still appears when a dim light source is used so that only one photon can pass at a time
  \item light exerts force
  \item light bent by gravity








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