而本題中質(zhì)量變了,而體積沒有變,根據(jù)密度公式,故選B例2、關(guān)于壓力,下列說法正確的是( C )A、壓在物體表面上的力叫壓力 B、壓力的大小一定等于物體的重力C、壓力的方向一定垂直于受壓物體表面 D、壓力的方向一定垂直于水平地面分析:選各種答案的學(xué)生都有,原因不理解是壓力的定義和方向?;煜龎毫椭亓Φ母拍?。
例4、如圖所示四個(gè)演示實(shí)驗(yàn)中,能夠說明電磁感應(yīng)現(xiàn)象的是( )又如:如下圖所示的四個(gè)實(shí)驗(yàn)裝置中,能反映出發(fā)電機(jī)原理的是( )A B C D分析:學(xué)生對(duì)課本實(shí)驗(yàn)不清楚,原理不理解例5、觀察下圖并填空。分析:有的教師對(duì)實(shí)驗(yàn)不夠重視,學(xué)生動(dòng)手能力差。
例6、已知硫酸的濃度越大,密度就越大,現(xiàn)將等體積90%和10%的硫酸溶液混合,所得溶液的溶質(zhì)質(zhì)量分?jǐn)?shù)為 ( A )A、>50% B、= 50% C、< 50% D、不能確定 分析:學(xué)生不理解溶質(zhì)質(zhì)量分?jǐn)?shù)例7、關(guān)于功和功率,下列說法正確的是( )A. 做功越多,功率一定越大 B. 做功時(shí)間越長,功率一定越大C. 做功越多,做功時(shí)間越長,功率一定越大D. 在相同的時(shí)間內(nèi)做功越多,功率越大分析:學(xué)生答題中有選A或B或C的,此題造成錯(cuò)解的主要原因是對(duì)功率概念理解不透。 功率的大小只表示物體做功的快慢,不表示做功的多少。
A. 機(jī)械能一樣大、內(nèi)能一樣大 B. 機(jī)械能一樣大、乙的內(nèi)能大C. 乙的機(jī)械能大、內(nèi)能一樣大 D. 以上答案都不正確分析:機(jī)械能包括動(dòng)能、勢(shì)能,兩個(gè)冰塊的質(zhì)量相同,可以通過它們的速度大小、位置高度,判斷它們的動(dòng)能和勢(shì)能的大小,判斷物體內(nèi)能大小的依據(jù)是溫度和狀態(tài)。根據(jù)題意,兩個(gè)冰塊均處于靜止?fàn)顟B(tài),它們的動(dòng)能都是零,兩冰塊質(zhì)量相同,乙冰塊比甲冰塊的位置高,乙冰塊的重力勢(shì)能大。
例10、關(guān)于光的傳播,下列說法中正確的是( )A. 光在空氣中才沿直線傳播 B. 光在任何情況下都沿直線傳播C. 光在玻璃中不是沿直線傳播 D. 光在同一種均勻物質(zhì)里沿直線傳播分析:學(xué)生容易選B,原因在于不明了光的直線傳播是有條件的,光在同一種均勻介質(zhì)中或在真空中才是沿直線傳播的。光不沿著直線傳播的事例可以舉出很多,如隔著盛滿水的玻璃杯看放在水中的筷子,筷子明顯彎折了,這就是光線發(fā)生了偏折的緣故。
1特殊疑問句 What's your name? –I'm Liu Ying. –My name is Liu Ying.What's your number? -I'm Number One.What class are you in? –I'm in Class Two What grade are you in? –I'm in Grade One What row are you in? –I'm in Row One.What row are they in? –They're in Row 7 What class is she in? –She's in Class One, Grade One What colour is your bag? –It's black.What's his number? -He's Number One, in Row One.What's one plus two? -It's three.What's this? -It is a clock.What's that in English? -It's a book.What're these? –They are books.What're those? –They are cups.What can you see in the picture? –I can see a clock What can she see? –She can see a dog.What's in the room? –There is a desk.Who is this? –This is Joy. Who is that? –That is David.Who's not here? –Ann is not here.Who isn't at school today? –Li Ming and Wei Fang Who's that girl? –That's my sister, Joy.Who's that man? –That's my father.Who's on duty today? –I am.How old are you? –I'm eleven.How old is she? –She's seven.How old is Polly? –It's two.How many children are there in your class? –66 How many pens do you have? –I have 2 pens.How are you? –I'm fine, thanks.How is your father? –He's well.How do you do? –How do you do?Where is she? –I think she's at home.Where is the washroom? –It's over there.Where are her photos? –They're on the wall.Which is your friend? –The one in a hat.Which boy is Tom? –The boy on the bike.Whose clock is this? -It's his.Whose is this clock? -It's his.Whose shoes are these? -They're mine.2.一般疑問句 Are you Lin Tao? –Yes, I am.Are you in Row 4? –Yes, I am.Are you ten? –Yes, I am.Are you English? –Yes, I am Are these your English books? –Yes, they are.Are those your pens? –Yes, they are.Are we all here? –Yes, we are Are they on her desk? –Yes, they are.Are there two boys in the room? –Yes, there are Are there any girls in the room? –Yes, there are.Is one plus two three? –Yes, it is.Is this a cup? –Yes, it is.Is that a ruler? –Yes, it is.Is it a cake? –Yes, it is.Is it on the desk? –Yes, it is.Is everyone here today? –Yes, we are.Is she at school today? –Yes, she is.Is this your pencil-box? –Yes, it is.Is that my cup? –No, it isn't.Is there a bag on the bed? –Yes, there is.Do you know? –Yes, I do.Can you spell your name? –Yes, I can.Can we put our coats here? –Yes, you can.Can I see your licence? –Yes, you can。