Question

如圖所示,R為電阻箱,為理想電壓表,當(dāng)電阻箱讀數(shù)為R₁=2 Ω時(shí),電壓表讀數(shù)為U₁=4 V;當(dāng)電阻箱讀數(shù)為R₂=5 Ω時(shí),電壓表讀數(shù)為U₂=5 V.求：

(1)電源的電動(dòng)勢(shì)E和內(nèi)阻r;

(2)當(dāng)電阻箱R讀數(shù)為多少時(shí),電源的輸出功率最大?最大值P_m為多少?

Answer 1

(1)E=6 V  r=1 Ω  (2)1 Ω  P_m=9 W

解析：(1)由閉合電路歐姆定律                     ①

                                             ②

聯(lián)立①②并代入數(shù)據(jù)解得E=6 V,r=1 Ω.

(2)由電功率表達(dá)式                             ③

將③式變形為                             ④

由④式知,當(dāng)R=r=1 Ω時(shí)P有最大值P_m==9 W.