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物理定律和物理公式是表示几个物理量之间的函数关系的等式,有些物理量之间的关系通过物理定律的物理公式可以看出有简单的比例关系。灵活地运用比例关系解物理习题,比用公式有时显得更为简捷。解决这类问题,要明确找出被比较的物理量之间的关系式,然后注意被比较的事物之间有什么共同点和不同点。例1,有固定电阻 R_1和一段电阻丝 R_2串联后接入电源内阻可忽略的电路中,如图1所示,已知 R_1和 R_2现在的功率之比为 P_1:P_2=2:1,若将 R_2对折后再接入电路,R~2的功率变为 P_2,求 P_2:P_2。(?)[分析与解]:初看,题目的已知似乎少些,R_1、R_2、电源电压一概未知,但既然求功率比,就应从各量间的关系去找。找比例,先在有共同特征的事物间去找。
The laws of physics and physics are equations that express the functional relationship between several physical quantities. The relationship between some physical quantities can be seen by the physical formula of physical laws as a simple proportional relationship. Flexible use of proportional relationships to solve physics exercises is sometimes more straightforward than using formulas. To solve such problems, we must clearly identify the relationship between the physical quantities being compared, and then pay attention to what are the common points and differences between the things being compared. In Example 1, there is a fixed resistance R_1 and a resistance wire R_2 connected in series after the power supply internal resistance is negligible in the circuit, as shown in FIG. 1, it is known that the power ratio of R_1 and R_2 is P_1:P_2=2:1, respectively. If R_2 is folded back into the circuit, the power of R~2 becomes P_2, and P_2:P_2 is required. (?) [analysis and solution]: At first glance, the problem seems to be less known, R_1, R_2, and the power supply voltage are unknown, but since the power ratio is sought, the relationship between the quantities should be found. To find proportions, first look for things that have common characteristics.