Physics education research, electronic materials, and the musings of Christopher Moore, Ph.D.

Maruko wrote:

Hi,

When we remove a resistor in series, the total resistance in the circuit decreases.  Does the total voltage increases in order to keep the total current constant?

When you remove a series resistor, you are replacing the resistor with an "open circuit," which has infinite resistance. In other words, it is as if you left the resistor in the circuit, but simply increased its value "to infinity." So, the total resistance increases (not decreases) "to inifinity." As  result, the current through the series connection doesn't remain constant—it drops to zero.

Maruko wrote:

If this is true, I am a little confused about the increase in voltage.  I thought that the battery determines the total voltage regardless of the number of resistor.

That is correct. The total voltage across the entire series connection of the resistors is equal to the voltage of the voltage source (i.e., the battery). The voltage across each resistor in the series connection depends on the size of that resistor relative to the total resistance of the series connection of resistors. Specifically, the voltage across any resistor is the ratio of its resistance to the total resistance of the series connection of the resistors, multiplied by the voltage of the voltage source.

Therefore, since removing one of the resistors is the same as leaving it in the circuit, but increasing its value "to infinity," the voltage across that "infinite resistance resistor" (i.e., the open circuit) is simply the voltage of the battery.

Vikash Jha wrote:

Voltage across a battery does not change because of change in resistance. Its the current which varies.So, in the series, if there is more resistance, there is less current as I=V/R.

Correct.

So if you remove a resistance in a series, net resistance decreses ....

Incorrect.