Physics Electricity Resistance increases.... (20 marks)

In a circuit, V represents the e.m.f. of the batteries (power supply).

As V is fixed, (Assume that you cannot alter the voltage supply of the batteries) By V = IR , When R increases, automatically, current will decrease.

First, a condition is missing. (the current is constant or the same)

When current is constant or the same
the resistance increase , the voltage will be higher.

" When R increases, the Voltage must increase in order to keep the same value of current. "

As you buy a battery, you just can see the Voltage Value on the surface, not the current value, right.

For example, if you use a power source(maybe a battery) which voltage is V and a Resistor which resistence value is R and use them to build DC circuit.

so the current value is I=V/R, if you buy another resistor and put them as series circuit.
the I=V/2R. In that situation, if you want keep the same current value, you must buy another battery to keep the same current.

當我們討論兩個物理量成正比時,一定要指明在甚麼條件之下.在 V=IR 一式中V與R成正比,顯然其中 I 必須維持不變. 因此 ,例如兩隻構造相同的燈泡(標定220V,40W)將它們串聯,此時總電阻變為二倍,要想它們都正常發光,即要使通過的電流不變,我們必須將電壓增至440V才可以.這就是你說的"電阻增加電壓要曾加"的例子,你必須注意其條件"電流保持不變"!!!
同理,在V不變條件下, I 與 R 成反比,也要注意其"V不變"的條件.