# Why positive or negtive pole of battery can not attract small objects ?

• magnetar
Q is the charge on the plates, and V is the voltage between the plates. If you think about it, a battery is like a capacitor with a lot of charge on it. So even if you only have a tiny amount of charge on a small object, the battery will still be able to attract it. In summary, the static charge on the terminals of a battery is not enough to attract small objects.

#### magnetar

why positive or negtive polar of battery can not attract small objects ?

you tell me why do you think it should?

Electrical and magnetic fields are not the same thing.

the terminals of a battery are at different potentials, that doesn't mean they would attract objects, they are not charged.

supratim1 said:
you tell me why do you think it should?

Because the positive pole accumulate positive charges, it should attract small objects as the charged rubber rod do ?

no, that's what i said...they don't accumulate positive charges. they are not charged. just that positive terminal is at higher potential than negative one. no charges.

i think what magnetar is asking is, if the charged ions or whatever they are are inside the battery are attracted to an electrode, why isn't anything outside the battery similarly attracted? I didn't realize you meant static related attraction. It's because a normal battery doesn't have enough voltage to attract small objects like a statically charged rod with high voltage.

rcgldr said:
It's because a normal battery doesn't have enough voltage to attract small objects like a statically charged rod with high voltage.

Now I'm confused. Voltage is relative.

One electrode has a potential difference of (say) 1.5 V from the other electrode.

But it has a high potential difference from "a statically charged rod with high voltage" …

so shouldn't that make it easier to attract an electron? If we bring an insulator with one free electron on its surface toward a battery, why isn't that attracted to one of the electrodes?

A battery is similar to an electric dipole. The potential difference between the battery poles is accompanied by an internal electric field. The interal electric field is caused by the electric charge polarization within the battery. Just like a capacitor.

A battery will have a nonzero surrounding electric field just like a capacitor, and will therefore (in principle) attract dielectric substances such as dust on both sides.

This was my understanding at least.

rcgldr said:
I didn't realize you meant static related attraction. It's because a normal battery doesn't have enough voltage to attract small objects like a statically charged rod with high voltage.

tiny-tim said:
Voltage is relative.
Assuming a moderate amount of capacitance, then a high voltage battery (if such a thing exists) would have signicant charge on at least at one of it's terminals. As mentioned above, batteries do attract dust.

i think its bcoz of the chemical inside... that even though it has static electricity in it...it has electric field not magnetic... if attached to a solenoid then it attracts objects like paper

Most batteries are electrochemical cells, with voltage controlled by varying the concentration of the ions. the EMF can be calculated using the Nernst equation.

when a conductor connects the two terminals, the electrons get a path to go to a higher potential (which they die to do). the battery creates an electrostatic field outside it, which makes the electrons move.

supratim1 said:
Most batteries are electrochemical cells, with voltage controlled by varying the concentration of the ions. the EMF can be calculated using the Nernst equation.

when a conductor connects the two terminals, the electrons get a path to go to a higher potential (which they die to do). the battery creates an electrostatic field outside it, which makes the electrons move.
and this causes magnetic field? NO. no magnetic field is created by the battery. but moving charges through the conductor creates a magnetic field.

hooww can battery create mg field? i stil don't get it

A battery not in a closed circuit (i.e. without a current running through it) does not create a magnetic field. I don't think anyone claimed that it did?

torquil said:
A battery not in a closed circuit (i.e. without a current running through it) does not create a magnetic field. I don't think anyone claimed that it did?
No one did. What was stated the terminals of a battery have a static charge, relative to the voltage (divided by the equivalent of capacitance) of the battery, and that the static charge is enough to attract dust.

rcgldr said:
No one did. What was stated the terminals of a battery have a static charge, relative to the voltage (divided by the equivalent of capacitance) of the battery, and that the static charge is enough to attract dust.

Yeah, I stated that myself in post #10. I wrote post #17 since I didn't understand the reason for the confusion in post #16...

i said it doesn't create any magnetic field.

magnetar said:
Because the positive pole accumulate positive charges, it should attract small objects as the charged rubber rod do ?

You're right, in principle the battery should attract or repel charged objects. The problem is that the amount of charge will be extremely tiny for a typical battery.

If you look at a normal battery, it has metal plates at the top and bottom. This essentially makes the battery a capacitor. The capacitance of a parallel plate capacitor is
$$C=\epsilon_{0}\epsilon_{r}\frac{A}{d}=\frac{Q}{V}$$
(This formula neglects edge effects which will be very prominent in a typical, say AA battery, but I just want to get an order of magnitude estimate)
In a device designed to be a capacitor, the distance between the plates will usually be extremely small, and filled with a material with a high dielectric constant to make Q relatively large. In a battery, 'd' will be something like 5cm, and the dielectric constant may or may not be significant, I'm not sure. For water the dielectric constant will be something like 80, which is relatively high, and you will see that this will not really make a difference in the fact that the force is extremely small. Let's take A=1cm^2, dielectric constant = 1, d = 5cm, V=1.5V. We get
$$Q \approx 2.6\cdot 10^{-14}coulombs$$
The force between two batteries separated by 1cm will be:
$$F=\frac{Q^2}{4\pi\epsilon_{0}r^2}\approx 6.1\cdot 10^{-14}N$$
So you can see the force is microscopic. Changing the dielectric constant to 100 could bring this up to 6*10-10, which is much bigger but still not readily observable.