What does it mean for an object to be positively charged

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There are two types of electric charges: positive and negative. Positively charged substances are repelled from other positively charged substances, but attracted to negatively charged substances. The electrostatic attraction between the positives and negatives brings the particles together and creates an ionic compound, like sodium chloride. A metal reacts with a nonmetal to form an ionic bond.

A positive charge occurs when the number of protons exceeds the number of electrons. A positive charge may be created by adding protons to an atom or object with a neutral charge. A positive charge also can be created by removing electrons from a neutrally charged object.

In a battery, the positive end (or cathode) is attractive to electrons, due to its positive charge. Metal loss at anodic sites in an electrochemical cell occurs when the metal atoms give up one or more electrons and move as positively charged ions into the electrolyte.

In a galvanic cell, positively charged ions flow to the cathode, while negative ions flow to the anode. In an electrical circuit, electric current is the movement of electrical charge. An atom's electric charge dictates how molecules react with each other and in nature.

When metal atoms are exposed to an environment containing water molecules, they can give up electrons, becoming positively charged ions, provided an electrical circuit can be completed. This effect can be concentrated locally to form a pit, or crack. It also can extend across a wide area to produce general wastage.

An electrical charge is created when electrons are transferred to or removed from an object. Because electrons have a negative charge, when they are added to an object, it becomes negatively charged. When electrons are removed from an object, it becomes positively charged.

What is an electrical charge?

An electrical charge is created when two materials come into contact or are rubbed together. When the materials are in contact, electrons can be literally rubbed off of one object and onto the other. This doesn’t mean that any two materials rubbed together will cause electrons to move. Some materials are much more willing to donate electrons, and others are much more likely to accept electrons. A list of materials ordered by their ability to donate electrons is called a triboelectric series.

Most of us have probably all generated a static electrical charge at some point in time. The shock you receive when you walk across a carpet and touch a metal surface or when you feel the cling of statically charged clothing are evidence of a static electrical charge.

Hair and rabbit’s fur give up electrons easily, whereas polyethylene and Teflon are good at attracting electrons. When two materials in different positions on the triboelectric series are rubbed together, the materials towards the positive end give up electrons and become positively charged, and those towards the negative end accept electrons and become negatively charged.

How do you create an electrical charge?

Consider a practical example of creating an electrical charge. When a balloon is rubbed on hair, electrons are moved from the hair to the surface of the balloon. The electrons ‘stick’ to the balloon where the balloon was rubbed and do not move across the surface of the balloon. The balloon becomes negatively charged (red electrons), and the person’s hair becomes positively charged (fewer electrons than before).

Now let’s use the newly charged balloon to charge another balloon. When we touch the charged balloon to a neutral (balanced – no extra electrons) balloon, some of the added electrons are transferred to the neutral balloon. Now both balloons have a negative charge, and we notice something – the balloons push apart. The charge on the balloons causes a force that pushes the balloons apart. The force is much like the repulsive force you feel when you bring two magnets together north to north or south to south.

Insulators and conductors

Insulators are materials such as glass, rubber, wood and most plastics where the electrons are held quite tightly and are not free to move easily from place to place. Conductors are materials such as copper, silver, gold and iron where electrons are free to move from place to place.

For example, a charged balloon (insulator) is brought near a neutral aluminium can (conductor). While the can is far away from the balloon, the negative charge on the balloon has little or no effect on the can, and the electrons on the can are evenly dispersed. When the balloon is brought near the can, something interesting happens – the electrons move to the side of the can to get as far away from the negatively charged balloon as possible. This leaves the side of the can nearest the balloon positively charged. The can as a whole is still neutral, but because the positively charged side of the can is close to the balloon, the negative charges on the balloon attract the positive side of the can and the force pulls the balloon and can together. If the can is lying on its side, it will roll towards the balloon.

Something quite different happens if the conducting can is allowed to touch the charged balloon. When the balloon and can touch, some of the electrons on the balloon will flow onto the can, leaving the can with extra electrons and therefore negatively charged. Now both the balloon and can are negatively charged, and the like charges cause a force pushing the can and balloon apart. If the can is lying on its side, it will roll away the balloon.

Induction

In the above example, we used a negatively charged balloon to impart a negative charge to the can by a process of direct contact. It is also possible to use a negatively charged balloon to impart a positive charge on a can through a process called induction.

If the balloon is brought near the can, the electrons move to the far side of the can, as described earlier. If another object, like a finger, now touches the negative side of the can, some of the overcrowded electrons will flow onto the object, leaving the can positively charged.

Thus it is possible to use a negatively charged balloon to impart either a negative charge (by contact with the balloon) or a positive charge (by induction).

Nature of science

In science, a model is a representation of an idea, an object or even a process or a system that is used to describe and explain phenomena that cannot be experienced directly. Models are central to what scientists do, both in their research as well as when communicating their explanations.

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This recorded professional learning session will build your confidence to teach Physical World.

Useful link

Use this University of Colorado simulation to experiment with electrical charges on balloons and other objects.

What does it mean when something is positively charged?

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