ECONMT 115 - CH3 - Static Electricity

Lightning (5)

1. Without doubt the greatest display of a static electric discharge. 2. A lightning bolt has an average voltage of about 15,000,000 volts. 3. Large rain drops become positively charged while small drops become negatively charged. 4. A thundercloud contains both + and - charged particles. 5. Most lightning discharges (lightning bolts) occur within the cloud.

Nuisance Static Charges - The static charge that accumulates on clothes in a dryer. (1)

The greatest static charges generally are built up on manmade fabrics because they are the best insulators and retain electrons more readily than natural fabrics such as cotton or wool.

Precipitator - Electronic Air Filter (1)

The precipitator uses a high-voltage DC power supply to provide a set of wires with a positive charge and a set of plates with a negative charge.

Static (1)

The word static means not moving or sitting still.

Testing for charge

With a charged electroscope, moving an object close to the metal ball will affect the leaves depending on the test object to the charged electroscope.

Lightning arrestor

1. A device for providing path by which lightning disturbances or other static discharges are passed to earth; this is primarily intended to prevent damage to electrical apparatus due to lightning. 2. Power lines are often protected by lightning arrestors that exhibit a very high resistance at the normal voltage of the line.

Useful Static Charges - Static electricity is often used in spray painting. (6)

1. A high-voltage grid is placed in front of the spray gun. 2. This grid has a positive charge. 3. The object to be painted has a negative charge (Figure 3-12). 4. As the droplets of paint pass through the grid, the positive charge causes electrons to be removed from the paint droplets. 5. The positively charged droplets are attracted to the negatively charged object. 6. This static charge helps to prevent waste of the paint and at the same time produces a uniform finish.

An electroscope is (4)

1. A metal ball attached to the end of a metal rod. 2. The other end of the rod is attached to two thin metal leaves. 3. The metal leaves are inside a transparent container to permit the action of the leaves to be seen and to prevent air currents from affecting their movement. 4. The metal rod is insulated from the box.

Useful Static Charges - Dry copy machine (5)

1. Another device that depends on static electricity is the dry copy machine. 2. The copy machine uses an aluminum drum coated with selenium. 3. Selenium is a semiconductor material that changes its conductivity with a change of light intensity. 4. When selenium is in the presence of light, it has a very high conductivity. 5. When it is in darkness, it has a very low conductivity.

Electrostatic charges (3)

1. Are built up on insulator materials because insulators are the only materials that can hold the electrons stationary and keep them from flowing to a different location. 2. A static charge can be built up on a conductor only if the conductor is electrically insulated from surrounding objects. 3. A static charge can be built up on a conductor only if the conductor is electrically insulated from surrounding objects.

Static electricity definition (4)

1. Caused by an imbalance of electrical charges (positive and negative). The imbalance occurs, then an object either gains or loses electrons. 2. Objects that gain electrons exhibit a negative charge, and objects that lose electrons exhibit a positive charge. 3. This electrical differential will exist until electrons on the negatively charged object move to the positively charged object. 4. When the electrons are equal on each object, there will no longer be a static charge.

Lightning can travel

1. Cloud to Cloud 2. Cloud to Ground 3. Ground to Cloud 4. Always negative to positive

A static charge can be (2)

1. Either positive or negative. 2. If an object has a lack of electrons, it has a positive charge; and if it has an excess of electrons, it has a negative charge.

Static electricity refers to (2)

1. Electrons that are sitting still and not moving. 2. Static electricity is therefore a charge and not a current.

Before the electroscope can be used (3)

1. It must first be charged - Either negatively or positively. 2. This is done by touching the ball with an object that has a known charge. 3. Example: Hard Rubber Rod is negatively charged touches the metal ball. The leaves turn negative and repel each other.

Static Electricity Observations (3)

1. Lightning without doubt the greatest display of a static electric discharge. 2. Static electricity can harm sensitive electronic components. 3. Generally a good idea to touch a grounded object to make certain that your body is discharged before handling these components.

Nuisance Static Charges - The static charge that accumulates on a person's body as he or she walks across a carpet. (3)

1. Most carpets are made from man-made materials that are excellent insulators such as nylon. 2. The dry air combined with an insulating material provides an excellent setting for the accumulation of a static charge. 3. This condition can generally be eliminated by the installation of a humidifier.

Lightning rods

1. Sometimes used to help protect objects from lightning. 2. Lightning rods work by providing an easy path to ground for current flow. 3. Invented by Benjamin Franklin.

Charging an Object

1. The charge that accumulates on an object is determined by the materials used to produce the charge. 2. If a hard rubber rod is rubbed on a piece of wool, the wool deposits excess electrons on the rod and gives it a negative charge. 3. If a glass rod is rubbed on a piece of wool, electrons are removed from the rod, thus producing a positive charge on the rod

Nuisance Static Charges - Drag Chain (2)

1. The static charge that accumulates on automobiles as they move through dry air. 2. One end of the drag chain is attached to the frame of the vehicle, and the other end drags the ground.