Why current drops when voltage increases?

Question

https://www.youtube.com/watch?v=ubZuSZYVBng&t=329s

In the video above the man put a 200 thousands volt ball near a non-charged one and a very tiny current appear between them. But I think with high electric potential difference between them, the ions should be pushed with higher force since F=q.E and thus more charge particles moving through a region per time which means higher current.

In reality there are many batteries that have the same voltage but different supply different currents. I know it has something to do with power but in my logic the battery is like a pump pushing electrons through conductor and it's voltage determines how much force it apply on the electrons to get them from cathode to anode which means with the same voltage they'll deliver the same amount of electrons. Somebody told me that it's like a narrow and a big water pipe under the same pressure, the bigger will let larger amount of water go through, however, if the pipe get narrower, isn't the current be faster?

Speaking of power. I still don't understand what exactly is it. A battery have a specific power but how does it control the voltage and the current? P = U1 x I1 = U2 x I2 = ... So if we rise the voltage, what causes the current to decrease? Just like the Earth and Mars, putting two objects in the same height on two planets, the object on Earth will have higher PE and thus fall faster just like ions travel at higher speed between higher voltage. So how is it possible that having a high potential difference cause the current to be smaller?

Answer 1

Regarding the video, the strong electric field causes the air between the charged sphere and the tip of the screw driver to break down, that is, causes the air ionize into positive ions and electrons resulting in current flow. The arc is then a low impedance path causing the voltage to drop.

In reality there are many batteries that have the same voltage but different supply different currents.

When different batteries having the same open circuit (no load) voltage, referred to as the battery emf, supply different currents to the same resistance it is because the batteries have different internal resistance which is in series with the resistor connected to its terminals. That is why a 1.5 v alkaline C battery delivers more current than a 1.5 v alkaline AAA battery. The internal resistance of the C cell is less than the AAA cell.

Speaking of power. I still don't understand what exactly is it. A battery have a specific power but how does it control the voltage and the current? P = U1 x I1 = U2 x I2 = ... So if we rise the voltage, what causes the current to decrease?

I'm having trouble making sense of this voltage rising and current falling. Not sure how it pertains to batteries. Your expression P = U1 x I1 = U2 x I2 looks like your describing the conservation of power for an ideal transformer where the 1 and 2 refer to the voltage and current of the two transformer windings.

With respect to batteries, the voltage and current delivered to a circuit by a battery is controlled by the battery emf and its internal resistance. The power a battery delivers to a load is the voltage across the battery terminals with the load connected times the current delivered to the load.

All real batteries have internal resistance. The same current that flows to the connected load also flows through its internal resistance. That means some of the power developed by the battery is dissipated by its internal resistance. The total power developed by the battery is then the sum of the power delivered to the connected load plus the power dissipated in its internal resistance.

Just like the Earth and Mars, putting two objects in the same height on two planets, the .......

From this point on I'm afraid I have no idea what you are getting at.

Hope this helps.

Answer 2

The current will depend, in a very complex way, on the potential difference (voltage) between to points. It's not necessarily linear. In some situations, there will be no measureable/noticeable current because the pathways for charge movement are blocked or non-existent.

If the current is linearly related to the voltage, we say that the pathway is Ohmic, that is, it obeys a relationship called Ohm's Law: $$I=VG = \frac{V}{R},$$ where

• $I$ is the current between two points,
• $V$ is the potential difference (voltage) between the two points,
• $G$ is a proportionality factor called the conductance
• $R$ is the more commonly mentioned resistance, which is the inverse of conductance

Other systems (like air) have non-linear relationships which can result in no current flow (effectively zero conductance, infinite resistance) until a certain voltage/(separation distance) is reached, then the effective resistance becomes extremely small (conductance becomes large).

Higher voltage does not cause smaller current. Smaller conductance causes smaller current.