Problem 13.36

พิจารณาแผนภาพอิสระของวัตถุ

T

\(\theta\)

qE

จาก \(\Sigma F_{x}= 0\)

mg

\(qE - Tsin\theta = 0\)

\(Tsin\theta = qE\cdots \cdots (1)\)

จาก \(\Sigma F_{y}= 0\)

\(Tcos\theta - mg = 0\)

\(Tcos\theta = mg\cdots \cdots (2)\)

\((1)/(2) ; \tan \theta =\frac{qE}{mg}\)

\(q =\frac{mgtan\theta}{E}\;\blacksquare\)