Trng THCS Trng Sn

Cng ngh: 8 Ngy son: 12/03/2012 Ngy dy: 15/03/2012

Tit 43: Bi 48: S DNG HP L IN NNGI. Mc tiu: 1. V kin thc: + Bit s dng hp l in nng + Hiu c nhu cu tiu th in nng 2. V k nng: 3. V thi : + C thi quen tit kim in nng + Lm vic nghim tc, khoa hc II. Chun b ca GV- HS: 1. Chun b ca GV: + Chun b k bi trc khi ln lp + Bng ph 2. Chun b ca HS: + c trc bi 48 III. Tin trnh t chc cc hot ng dy hc: 1. n inh t chc, kim tra s s lp 2. Kim tra bi c: ? Hy nu cu to ca my bin p? ? Khi dng my bin p cn ch nhng g? 3. Gii thiu bi mi: Ngy nay, in nng c s dng rng ri trong mi lnh vc ca i sng nh: cng s, gia nh, nh my,.... V khon chi ph m chng ta phi tr hng thng cng khng phi t khi m gi in ngy cng tng. V th nn chng ta phi s dng in nng hp l. Vy s dng in nng th no cho hp l? cng chnh l ni dung ca tit hc hm nay. 4. Bi mi: Hot ng 1: Tm hiu nhu cu tiu th in nng Hot ng ca GV-HS Ni dung GV: GV yu cu HS nghin cu SGK v cho I. Nhu cu tiu th in nng bit: Do thi quen sinh hot v lm vic ca mi 1. Gi cao im tiu th in c nhn hay c quan t chc m nhu cu s nng dng in nng trong ngy khc nhau - Gi cao im l nhng gi tiu ? Theo em th thi gian no trong ngy s dng th in nng nhiu trong ngy nhiu in? HS: Tr li GV: KL: T 18h -> 22h GVHD: Nguyn Th Anh ThpdfMachine A pdf writer that produces quality PDF files with ease! Produce quality PDF files in seconds and preserve the integrity of your original documents. Compatible across nearly all Windows platforms, if you can print from a windows application you can use pdfMachine. Get yours now!

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Trng THCS Trng Sn GV: ? Theo em th thi gian no trong ngy s dng t in? HS: Tr li GV: KL: Khong thi gian cn li trong ngy GV: Vy gi cao im l nh th no? HS: Tr li GV: KL: gi cao im l nhng gi tiu th in nng nhiu trong ngy. GV: Vy khong thi gian no c tnh l gi cao im? HS: Tr li GV: KL: gi cao im l khong thi gian t - Khong thi gian trong ngy h h 18 -> 22 . 18h -> 22h l gi cao im GV: Ti sao khong thi gian t 18h -> 22h li c xem l gi cao im? HS: Tr li GV: KL: V gi s dng nhiu dng in nh: Bng n, qut in, ni nu cm, my bm nc,... GV: Yu cu HS quan st SGK v cho bit: ? 2. Nhng c im ca gi cao Gi cao im c nhng c im g? im HS: Tr li - in nng tiu th rt ln trog GV: KL: khi kh nng cung cp in ca - in nng tiu th rt ln trog khi kh nh my in khng p ng nng cung cp in ca nh my in - in p ca mng in b gim khng p ng xung nh hng n ch - in p ca mng in b gim xung lm vic ca dng in. nh hng n ch lm vic ca dng in Hot ng 2: Tm hiu cch s dng hp l v tit kim in nng Hot ng ca GV-HS Ni dung GV: Cho HS nghin cu SGK v cho bit: ? II. S dng hp l v tit kim Theo em c cc bin php no s dng hp l in nng in nng? 1. Gim bt tiu th in nng HS: Tr li trong gi cao im GV: KL: C 3 bin php c bn m SGK nu gim bt in nng trong gi l: cao im ta phi ct 1 s - Gim bt tiu th in nng trong gi cao dng in khng thit yu. im Vd: Ct in bnh nng lnh, l - S dng dng in hiu sut cao si, tt 1 s n khng cn tit kim in nng thit, khng l qun o, khng

Cng ngh: 8

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Trng THCS Trng Sn - Khng s dng lng ph in nng GV: Theo em ti sao phi gim bt tiu th in nng trong gi cao im? HS: Tr li GV: KL: trnh tt in p GV: Vy gim bt in nng trong gi cao im ta cn phi lm g? HS: Tr li: GV: KL: gim bt in nng trong gi cao im ta phi ct 1 s dng in khng thit yu. GV: Nu thm 1 s v d GV: V sao phi s dng dng in hiu sut cao? HS: Tr li GV: V nh th s tit kim c in nng GV: V sao hin nay ngi ngi nh nh thng dng n hunh quang thay cho n si t? V sao? HS: Tr li GV: KL: V n hunh quang tiu th in nng t hn 4- 5 ln so vi n si t GV: GV nu 1 s v d cho HS sau treo bng ph cho HS tr li bm nc,...

Cng ngh: 8

2. S dng dng in hiu sut cao tit kim in nng - dng in hiu sut cao s t tn in nng

3. Khng s dng lng ph in nng Khng s dng dng in khi khng c nhu cu - Tan hc khng tt n phng hc LP - Khi xem ti vi, tt n bn hc tp TK - Bt n phng tm, phng v sinh sut ngy m LP - Khi ra khi nh, tt in cc phng. TK

4. Cng c - Cho HS c phn ghi nh - Tr li cu hi cui bi 5. Cng vic v nh - c trc bi 49 - Hc bi c

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