U_BC= 400 V; BC = 10 cm; α = 60^o; tam giác ABC vuông tại A như hình vẽ. Tính cường độ điện trường E.

\(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqababaaaaaaa % aapeqaaiaadghacaqGGaGaeyypa0JaaeiiaiaaigdacaaIWaWdamaa % CaaaleqabaWdbiabgkHiTiaaiMdaaaGccaGGGcGaam4qaiaacUdaca % qGGaGaamyCaiaacEcacaqGGaGaeyypa0JaaeiiaiaaiMdacaGGUaGa % aGymaiaaicdapaWaaWbaaSqabeaapeGaeyOeI0IaaGymaiaaicdaaa % GccaGGGcGaam4qaiaacUdacaWGvbWdamaaBaaaleaapeGaamOqaiaa % doeaa8aabeaakiabg2da98qacaqGGaGaaGinaiaaicdacaaIWaGaae % iiaiaadAfacaGG7aGaaeiiaiaadkeacaWGdbGaaeiiaiabg2da9iaa % bccacaaIXaGaaGimaiaabccacaWGJbGaamyBaiaacUdacaqGGaGaeq % ySdeMaaeiiaiabg2da9iaabccacaaI2aGaaGima8aadaahaaWcbeqa \begin{array}{l} q{\rm{ }} = {\rm{ }}{10^{ - 9}}\;C;{\rm{ }}q'{\rm{ }} = {\rm{ }}{9.10^{ - 10}}\;C;{U_{BC}} = {\rm{ }}400{\rm{ }}V;{\rm{ }}BC{\rm{ }} = {\rm{ }}10{\rm{ }}cm;{\rm{ }}\alpha {\rm{ }} = {\rm{ }}{60^o};\\ {U_{AC}} = \frac{{{A_{AC}}}}{q} = E.AC.cos{90^o}\; = {\rm{ }}0.\\ {U_{BA}} = {U_{BC}} + {U_{CA}} = {U_{BC}} = 400V \end{array}\)\(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqababaaaaaaa % aapeqaaiaadghacaqGGaGaeyypa0JaaeiiaiaaigdacaaIWaWdamaa % CaaaleqabaWdbiabgkHiTiaaiMdaaaGccaGGGcGaam4qaiaacUdaca % qGGaGaamyCaiaacEcacaqGGaGaeyypa0JaaeiiaiaaiMdacaGGUaGa % aGymaiaaicdapaWaaWbaaSqabeaapeGaeyOeI0IaaGymaiaaicdaaa % GccaGGGcGaam4qaiaacUdacaWGvbWdamaaBaaaleaapeGaamOqaiaa % doeaa8aabeaakiabg2da98qacaqGGaGaaGinaiaaicdacaaIWaGaae % iiaiaadAfacaGG7aGaaeiiaiaadkeacaWGdbGaaeiiaiabg2da9iaa % bccacaaIXaGaaGimaiaabccacaWGJbGaamyBaiaacUdacaqGGaGaeq % ySdeMaaeiiaiabg2da9iaabccacaaI2aGaaGima8aadaahaaWcbeqa % a8qacaWGVbaaaOGaai4oaaqaaiaadwfadaWgaaWcbaGaamyqaiaado % eaaeqaaOGaeyypa0ZaaSaaaeaacaWGbbWaaSbaaSqaaiaadgeacaWG % dbaabeaaaOqaaiaadghaaaGaeyypa0Jaamyraiaac6cacaWGbbGaam \begin{array}{l} q{\rm{ }} = {\rm{ }}{10^{ - 9}}\;C;{\rm{ }}q'{\rm{ }} = {\rm{ }}{9.10^{ - 10}}\;C;{U_{BC}} = {\rm{ }}400{\rm{ }}V;{\rm{ }}BC{\rm{ }} = {\rm{ }}10{\rm{ }}cm;{\rm{ }}\alpha {\rm{ }} = {\rm{ }}{60^o};\\ {U_{AC}} = \frac{{{A_{AC}}}}{q} = E.AC.cos{90^o}\; = {\rm{ }}0.\\ {U_{BA}} = {U_{BC}} + {U_{CA}} = {U_{BC}} = 400V \end{array}\)

 Cường độ điện trường E: \(E{\rm{ }} = \frac{{{U_{BC}}}}{{BCcos\alpha }} = {\rm{ }}{8.10^3}\;V/m.\)