「每日一練」 IB物理例題解析及練習Capacitor

「每日一練IB Physics」

今日知識點：Capacitor

例題

A capacitor of capacitance C discharges through a resistor of resistance R. The graph shows the variation with time t of the voltage V across the capacitor.

The capacitor is changed to one of value 2C and the resistor is changed to one of value 2R. Which graph shows the variation with t of V when the new combination is discharged?

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解析

此題考察的是discharge circuit中potential difference, V和time, t的關系。實際上，Q, V, I都與t有著十分類似的關系，可以一起記下來。

where time constant, τ=RC

而本題中，R與C都增加了兩倍，independent variable與原先相比減小到1/4，由數學中Transformation的知識可以得出，graph experiences horizontal stretch by a factor of 4，故選項B為正解。

下面翰林小助手為大家準備了一道同類型的題目，請大家一起來試試解答。

Your turn

A fully charged capacitor is connected to a resistor. When the switch is closed the capacitor will discharge through the resistor.

Which graphs correctly show how the charge on the capacitor and the current in the circuit vary with time during the discharging of the capacitor?

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Correct Answer：A