Electric Circuits – Does Resistance Affect Voltage?

batterieselectric-circuitselectric-currentelectrical-resistancevoltage

I have looked this up and what followed was that resistance does not affect the voltage of a circuit. But lets say we have a power source of 5V flowing at 1 Amp. The neccesary resistance of this circuit must be 5 $\Omega$ to decipate the energy of the eletrons before they get to the negative terminal of the source. So this is referred to as the voltage drop across the resistor but has this not affected the voltage by reducing the energy of the flowing charge?

Best Answer

"[R]esistance does not affect the voltage of a circuit."

I suspect that the writer had in mind what happens when you connect different resistances across a power supply. A good power supply is built to give a roughly constant voltage across its terminals – a voltage that hardly changes when you change the resistance of the load (that is whatever it is that you connect across the terminals) – provided that you don't make the load resistance too low.

A lower load resistance, $R$ will just increase the current according to $$I= \frac {V_{\text{terminal}}}{R_{\text{load}}}$$

Even an ordinary battery will provide a roughly constant voltage across its terminals, provided that you don't connect a load that has too low a resistance across its terminals. In fact the terminal voltage is given, fairly accurately, by $$V_{\text{terminal}}=\mathscr E - Ir$$ $\mathscr E$ is called the emf of the battery, and is the voltage across its terminals when you are drawing no current. $r$ is called the internal resistance of the battery.

Example: Suppose a battery has an emf of 9.0 V and an internal resistance of 0.5 ohm. What will be the terminal voltage if you connect a 4.0 ohm resistor across its terminals? $$V_{\text{terminal}}=9.0\ \text V - I \times 0.5\ \Omega \ \ \ \ \ \ \text{but}\ \ \ \ \ \ \ V_{\text{terminal}}=I \times 4.0\ \Omega$$ Solving, $I=2.0$ A, $V_{\text{terminal}}=8.0$ V. If you repeat for an 8 ohm resistor connected across the terminals of the same battery, you will find that $V_{\text{terminal}}$ isn't much different!

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