老师在办公室经常有这样的感慨,这个题目讲过学生怎么还不懂,从来听不到老师反思:这个题目在课堂上讲解不到位,导致学生没有听懂,没有理解.由此可见,反思教学多么重要,讲题不在多,而在于要讲透.下面以一例题的评讲为例谈如何将题目讲透.例在研究“一定电压下,电流与电阻的关系”时,电路如图1所示.电源电压恒为6 V.滑动变阻器上标有“20Ω1.5 A”字样.在a、b两点间先后接入不同阻值的定值电阻,闭合开关,移动滑片P,使电压表示数为3 V,读出电流表的示数.当30Ω的电阻接入a、b间时,电压表示数始终无法达到3 V.其原因可能是A.控制电压为3 V太高B.滑动变阻器的最大阻值太大C.30Ω的电阻阻值太大D.电源电压6 V太低 Teachers in the office often have such feelings, the students talk about how the problem did not understand, never hear the teacher reflection: This topic is not explained in the classroom, leading to students did not understand, did not understand. Thus, the reflective teaching How important is the topic is not much, but rather to be transparent. The following example of a comment on how to talk about the subject. In the study of “a certain voltage, the relationship between current and resistance,” when the circuit Shown in Figure 1. Power supply voltage constant 6 V. Slide varistors marked with “20Ω1.5 A ” in the a, b between the two have access to different resistance value of the resistance, the closure of the switch, sliding Piece P, make the voltage indication number is 3 V, read out the indication of the ammeter .When the resistance of 30Ω connects a, b, the voltage indication number can not reach 3 V. The reason may be A. The control voltage is 3 V Too high B. The maximum resistance of the sliding rheostat is too large C. The resistance of the 30Ω resistor is too large D. The supply voltage is too low