In Fig. $22-64 a,$ a particle of charge $+Q$ produces an electric field of magnitude $E_{\text { part }}$ at point $P,$ at distance $R$ from the particle. In Fig. $22-64 b,$ that same amount of charge is spread uniformly along a circular arc that has radius
$R$ and subtends an angle $\theta$
The charge on the arc produces an electric field
of magnitude $E_{\mathrm{arc}}$ at its center of curvature $P .$ For what
value of $\theta$ does $E_{\text { arc }}=$
0.500$E_{\text { part? }}$ (Hint: You will
probably resort to a graphical solution.)