Science 9 Static Electricity Static Electricity Page

Static Electricity Static electricity is a build-up of electric charge that does not move (it stays in place). Static means stationary or still.

Effects of Static Electricity

The Explanation (Theory) for Static Electricity All substances are composed of atoms. Atoms have a small but heavy positive center (the nucleus). Around the nucleus are light, moving, negative electrons.

A Review of the Charge Laws Like charges repel each other. Opposite charges attract each other.

Outer Electrons Can Escape Electrons in the outer shells of atoms are not held as strongly as inner electrons. Outer shell electrons can be pulled away from an atom by friction, when one object rubs another.

The Explanation (Theory) for Static Electricity Normal substances are neutral because their atoms have the same number of positive charges (protons) as negative charges (electrons).

When Electrons Transfer, Objects Become Charged When electrons move into a neutral object, it becomes negatively charged. When electrons move out of a neutral object, the object becomes positively charged.

Grounding an Object Grounding is usually used to remove the charge build-up on an object but it can also be used to charge an object (This will be discussed later.). When an object is grounded, it is connected by means of a conductor (metal) to some other much larger object (often the earth or ground). Electrons are free to move into or out of the ground into the object until it

Grounding an Object Grounding removes a charge as long as the grounding object is larger than the discharging object. For example, a tiny pith ball is neutralized when a person touches it (the person’s body is huge compared to the tiny pith ball.)

Insulators Substances that hold a static charge when rubbed are called insulators. Dry air, glass, plastic, cloths, wood, paper and rubber are insulators. Insulators hold electrons in place and do not let them wander or move about. Grounding a charged insulator (connecting it to a large object) will NOT remove the charge.

Conductors Conductors will NOT hold a static charge when rubbed. Metals and graphite (pencil lead) are good conductors. Conductors allow their electrons to roam freely through them. Conductors will hold a static charge if they are insulated. Grounding a charged, insulated conductor will remove the conductor’s charge.

The Effect of Charged Objects on Conductors Charged objects induce (cause) charges to separate in neutral conductors.

The Explanation (Theory) for Static Electricity In solid materials, the positive centers are fixed in place, just vibrating. This means that the positive charges (protons) do not move. The negative charges (electrons) are light and are able to move from place to place. (phet demos)

The Explanation (Theory) for Static Electricity Different substances have different attractions for electrons. For example, the atoms in plastics tend to attract electrons more strongly while the atoms in wool tend to have a weaker attraction for electrons.

The Explanation (Theory) for Static Electricity When objects are rubbed together, electrons move towards the substance which has the greater attraction for electrons. This leaves one object negative and the other object equally positive.

The Triboelectric Series The Triboelectric Series is a chart that shows the charge that objects will get when rubbed together. When wool and plastic (PVC) are rubbed, the wool becomes positive and the plastic becomes negative.

The Electroscope An electroscope is a device used to detect the kind and amount of electric charge on a charged object.

Bringing a Charged Object Near an Electroscope The leaves of a neutral electroscope separate when a charged object approaches the electroscope. This happens because the charged object repels electrons into the leaves, making them the same charge which causes them to repel away from each other.

Charging an Electroscope by Conduction When a neutral electroscope is touched by a charged object, it becomes charged with the same charge as the charged object that touched it. This is called charging by conduction or charging by contact.

Charging by Conduction With Negative Object When a neutral electroscope is touched by a negatively-charged object, some electrons move from the negative rod into the electroscope so that it gets the same charge as the object that touched it.

Charging by Induction An electroscope is charged by induction when a charged object is brought close to it but DOES NOT touch it and then the electroscope is grounded (connected to a large conductor or the earth via pipes/wires).

Charging by Induction When an electroscope is charged by induction, it gets a charge that is opposite the charge on the charged object that is brought close to the electroscope.

Neutral Objects Always Attract to Charged Objects Charged objects brought near to neutral objects cause the neutral objects to separate their charges so that the opposite charge faces the charged object.

Neutral Objects Always Attract to Charged Objects Since a neutral object separates its charges with the opposite charge facing the charged object, it will always attract to the charged object since it takes on the opposite charge.

Using Static Electricity: A Photocopier A photocopier uses static electricity to make an invisible electrostatic image on a paper and attract oppositely-charged powder to this paper, using heat to bond the powder to the paper.

Using Static Electricity: A Photocopier A photocopier uses static electricity to make an invisible electrostatic image on a paper and attract oppositely-charged powder to this paper, using heat to bond the powder to the paper.

Using Static Electricity: Removing Pollution Electrostatic precipitators help to remove pollution from air (in factory stacks or in homes – dust removal).

Using Static Electricity: Efficient Painting Paint is given one charge and the object to be painted is given an opposite charge. The paint attracts to the object.

Controlling Static Electricity: Preventing Sparks Many vehicles have ground strips to prevent a build-up of static charge (could cause sparks that could ignite gasoline fumes). Tanker trucks typically have grounds in their hoses to stop the formation of sparks.

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