题目内容
(1)当开关掷向1时,电压表示数为3V,此时电阻箱的电阻为6Ω,求R2上电流在1min内产生的热量是多少?
(2)当开关掷向2时,灯泡恰好正常发光,电压表读数为原来的2倍,求灯泡的额定电压和额定功率。
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(1)180J(2)3V 6W
(1)开关接1,R1、R2串联
∴U1= U-U2="9" V—3 V="6" V ----(1分)
∴I1 =U1/R1=6V/6Ω="1A" = I2 ----(1分)
∴R2= U2/ I2= 3 V/ 1 A =3Ω ----(1分)
∴Q2= U2I2t=3 V×1 A×60s ="180J " ----(1分)
(2)开关接2,L、R2串联
L正常 UL= U-U2〃="9" V—6 V="3V " ----(1分)
I2〃 =U2〃/R2=6V/3Ω="2A" = IL ∴PL=UL IL="3" V×2A=6W ----(1分)
∴U1= U-U2="9" V—3 V="6" V ----(1分)
∴I1 =U1/R1=6V/6Ω="1A" = I2 ----(1分)
∴R2= U2/ I2= 3 V/ 1 A =3Ω ----(1分)
∴Q2= U2I2t=3 V×1 A×60s ="180J " ----(1分)
(2)开关接2,L、R2串联
L正常 UL= U-U2〃="9" V—6 V="3V " ----(1分)
I2〃 =U2〃/R2=6V/3Ω="2A" = IL ∴PL=UL IL="3" V×2A=6W ----(1分)
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