Why do voltages seem to behave differently than expected?

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In summary, voltages are measured between two points in a circuit and depend on the resistance of the circuit elements in between. The voltage at a particular point in the circuit is not necessarily equal to the voltage at another point in the circuit. The voltage at the negative terminal is greater than the voltage at the positive terminal. The voltage at the negative pole is zero because the electric potential energy of a charge is negative.
  • #1
Haftred
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I am very confused right now about voltages. When I plug in a power supply and set it to an arbitrary voltage, I measure voltages between 0 and what I set it to. However, shouldn't it be that the closer I get to the positive terminal of the power supply, the closer the voltage gets to infinity. If V=(kq)/r then as r approaches 0, V should approach infinity; however, this is not seen. Also, why should the voltage be equal to zero at the negative pole? The negative charge is doing -work against the positive charges, so shouldn't V approach -infinity? Thanks to anyone who can clarify this for me.
 
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  • #2
What do you mean by voltage? Potential or potential difference?

I think Potential difference is the significant term. Potentia difference is the measure of the energy difference of unit charge between two points. Like mgh is the difference in the gravitational potential energy of a body of mass m between two points. Otherwise the gravitational potential energy at the surface of Earth will be zero, which is not true as we know.

Now think again of your question.
 
  • #3
Haftred said:
I am very confused right now about voltages. When I plug in a power supply and set it to an arbitrary voltage, I measure voltages between 0 and what I set it to. However, shouldn't it be that the closer I get to the positive terminal of the power supply, the closer the voltage gets to infinity. If V=(kq)/r then as r approaches 0, V should approach infinity; however, this is not seen. Also, why should the voltage be equal to zero at the negative pole? The negative charge is doing -work against the positive charges, so shouldn't V approach -infinity? Thanks to anyone who can clarify this for me.
I take it you're measuring voltages with two leads - a ground and the probe that gives you a voltage. What you're measuring is the voltage difference between the two leads. If the two leads are hooked up next to each other, naturally there's no difference and your measured voltage is zero. If you were to hook the ground lead up somewhere in the middle of the circuit, your probe would give you a negative voltage at the negative terminal.

The point you measure at doesn't determine the resistance. The resistors (and/or other elements) are still in the circuit regardless of where you measured from. In other words, it doesn't matter where you measure the voltage, the resistance in the circuit doesn't change. You're measuring the circuit, not modifying it (okay, technically, not quite true - it's impossible to measure a circuit without modifying it, but you're at least not modifying the values you're measuring).
 
  • #4
Haftred,
It is questions like these that can send one around the bend! Let's try anyway. Firstly the formula for voltage (electric potential difference) that you refer to applies to a point charge, which is not applicable here. Secondly when we talk about potential difference one may choose your zero reference level arbitrarily (usually at the negative terminal of the circuit). Then the electric potential of the power supply would be the amount of work one needs to do in order to move 1 coulomb of positive charge from the negative terminal through the circuit to the positive terminal of the power supply. The "voltage" of the power supply is therefore the amount of work that one coulomb of positive charge would do in the circuit when it is driven by the power supply through the circuit. This "capacities" of power supplies differs due to their abilities to generate electric fields of different magnitudes in the circuit components (which pushes the charge through the components). I hope this helps to ease the pain a bit.
 

Related to Why do voltages seem to behave differently than expected?

1. What is the difference between voltage and electric potential?

Voltage and electric potential are two related but distinct concepts. Voltage refers to the potential energy difference between two points in an electric field, while electric potential is the potential energy per unit charge at a specific point in an electric field. In other words, voltage is the difference in electric potential between two points, while electric potential is the amount of potential energy at a specific point.

2. How do I measure voltage?

Voltage can be measured using a voltmeter, which is a type of electrical measuring instrument. The voltmeter is connected in parallel to the circuit or component being measured, and it measures the potential difference between two points in the circuit.

3. Can voltage be negative?

Yes, voltage can be negative. In the context of a circuit, a negative voltage indicates that the direction of current flow is opposite to the direction of conventional current flow (from positive to negative). In physics, negative voltage can also refer to a decrease in electric potential energy from one point to another.

4. How does voltage affect the flow of electric current?

Voltage is what drives the flow of electric current through a circuit. It creates an electric field that causes charged particles (such as electrons) to move from an area of higher potential energy to an area of lower potential energy. The higher the voltage, the greater the force on the charged particles, and the greater the current flow.

5. What is the relationship between voltage and power?

Voltage and power are related through Ohm's law, which states that the current through a conductor is directly proportional to the voltage and inversely proportional to the resistance. This means that for a given amount of power, increasing the voltage will result in a decrease in current, and vice versa. In other words, power (in watts) equals voltage (in volts) multiplied by current (in amps).

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