Chuyen de dien hoc.

Bai tap phan :Dien hoc.
Bai tap vat li va trong tuoi tre:Mot mach dien gom ba dien tro da biet R1=20 om,R2=30 om ,R4 =60 ommot dien tro chua biet R3 va mot bien tro mac giua hai diem C va D(hinh ve).Khi do dien tro Rab giua A vaB nguoi ta thay rang no khong phu thuoc vao do lon cua bien tro.Tim dien tro R3 va dien tro Rab?
Mot bai toan nho nhung dang de luu y:Mot n tro co gia triR=100 om dong dien chay qua dien tro duoc tinh theo cong thuc:I=2nhan can bac hai cua t.Trong do I la gia tri cuong do dong dien con t la thoi gian.Neu nhiet luong toa ra tren dien tro la1,8kj thi thoi gian dong dien chay qua dien tro la bao nhieu?
Tiep tuc mot bai tap cong suat:Mang dien trong mot khu nha gom mot bong den 110vmac song song ,duong day tai dien noi toi tram bien the cach xa1,2kmgom hai day nhom co p=2,5.10^-8 ommet,tiet dien 80mm met vuong .Coi hieu dien the ra tu tram bien the la khong doi va bo qua dien tro cac day noi trong khu nha .
A,khu nha dung 44 den loai 60w ,cac den sang binh thuong :
-tinh cong suat hao phi tren duong day va hieu suat cua mang den.
-neu cam them mot bep dien thi do sang cua den thay doi nhu the nao?taisao?
B,neu khu nha muon dung 56 bong den cac loai :40w,60w,150w,ma van sang binh thuong thi can co bao nhieu den moi loai?{baif tapj treen laf baif tapj mootj deef thuws 11 trong sachs tuyeenr sinh}
Bien tro ghe gom ;Bai tap nay co trong mot so de thi nhu:hsg tinh Phu Tho (2010_2011);hsg tinh Vinh Phuc(1996_1997)(2002_2003)..May bai tap nay khong kho cho lam neu ta biet van dung dunh ki nang.Nhung thuong de giai ra thi hoi dai,lang nhang rat de gay nham lan.
Cong –cong suat –cong suat cuc dai:Mot so bai tap nhu
Bo phan dot nong cua am dien gom 4 day may xo giong nhau,moi day co dien tro 4 om,am duoc mac vao nguon dien co hieu dien the U=100 V bang day dan co dien tro 4 om.Hoi trong tat ca ca cach mac thi cach mac nao lam cho nuoc trong am dien soi nhanh hon,khi do cong suat tieu thu cua am dien la bao nhieu? Bai giai:
Ki hieu dien tro cua am dien la Rx,dien tro cua day dan la Rd,hieu dien the cua nguon laU.Khi do cong suat toa nhiet cua am la:Px=(U/Rd+Rx)^2.Rx=U ^2/(Rd/can bac2 Rx +can bac 2 Rx)^2=100^2/(4/can bac 2Rx+can bac 2 Rx)^2.Nuoc trong am trong soi hon khi cong suat toa nhiet cua am la lon nhat.Tu bieu thuc tren muon cong suat toa nhiet cua am la lon nhat thi mau suat cua bieu thuc phai nho nhat.Nhan xet :4/can bac 2Rx.can bac 2 Rx =4 co gia tri la mot hang so nen theo bat dang thuc Co-si thi tong cua chung nho nhat khi va chi khi:4/can bac 2 Rx=Rx hay Rx=4om.Vi Px gom 4 day,moi day co dien tro 4 om nende nuoc chong soi cac day trong am phai mac thanh 2 nhanh,moi nhanh gom 2 day mac noi tiep voi nhau hoac 2 day mac song song noi tiep voi 2 day mac song song.Khi do cong suat tieu htu tren am laPx=625W. The end.
Mot bai tap ve mac mach dien:co 2 bong den ghi220v-15Wva 220V-75w,mot cong tac.Hay ve so do mach dien sao cho khi cong tac dong chi mot den sang ,khi cong tac mo chi den kia sang.Biet rang neu cong suat tieu thu tren den nho hon1/10 cong suat dinh muc cua nothi den khong sang.Hay chung minh so do mach dien da ve la dung.Bai giai:
Den D1vaD2 khong the mac song song hoac noi tiep voi nhauva cong tac o mach chinh vi khi do chung se cung sangkhi cong tac dong hoac cung tat khi congtac mo.Vay hai den phai mac noi tiep va cong tac mac song song voi mot den( hinh ve ) tat ca maac noi tiep vao nguon dien U.
-Khi dong k thi den 1(220V-15w)bi noi tat nen khong sang.Hieu dien the tren den d2(220v-75w)bang U.Theo bai ra Ptieu thu>=75/10 w thi den d2 sang.Khi