Static Electricity Pdf

[Otilia Mojarro]

Thereforeall things are made up of charges. Opposite charges attract each other (negative to positive). Like charges repel each other (positive to positive or negative to negative). Most of the time positive and negative charges are balanced in an object, which makes that object neutral.

Static electricity is the result of an imbalance between negative and positive charges in an object. These charges can build up on the surface of an object until they find a way to be released or discharged. One way to discharge them is through a circuit.

When you rub a balloon against your clothes and it sticks to the wall, you are adding a surplus of electrons (negative charges) to the surface of the balloon. The wall is now more positively charged than the balloon. As the two come in contact, the balloon will stick because of the rule that opposites attract (positive to negative).

Static electricity is an imbalance of electric charges within or on the surface of a material. The charge remains until it can move away by an electric current or electrical discharge. The word "static" is used to differentiate it from current electricity, where an electric charge flows through an electrical conductor.[1]

Materials are made of atoms that are normally electrically neutral because they contain equal numbers of positive charges (protons in their nuclei) and negative charges (electrons in "shells" surrounding the nucleus). The phenomenon of static electricity requires a separation of positive and negative charges. When two materials are in contact, electrons may move from one material to the other, which leaves an excess of positive charge on one material, and an equal negative charge on the other. When the materials are separated they retain this charge imbalance. It is also possible for ions to be transferred.

Electrons or ions can be exchanged between materials on contact or when they slide against each other, which is known as the triboelectric effect and results in one material becoming positively charged and the other negatively charged. The triboelectric effect is the main cause of static electricity as observed in everyday life, and in common high-school science demonstrations involves rubbing different materials together (e.g., fur against an acrylic rod). Contact-induced charge separation causes one's hair to stand up and causes "static cling" (for example, a balloon rubbed against the hair becomes negatively charged; when near a wall, the charged balloon is attracted to positively charged particles in the wall, and can "cling" to it, suspended against gravity).

Heating generates a separation of charge in the atoms or molecules of certain materials. All pyroelectric materials are also piezoelectric. The atomic or molecular properties of heat and pressure response are closely related.

A charged object brought close to an electrically neutral conductive object causes a separation of charge within the neutral object. This is called electrostatic induction. Charges of the same polarity are repelled and move to the side of the object away from the external charge, and charges of the opposite polarity are attracted and move to the side facing the charge. As the force due to the interaction of electric charges falls off rapidly with increasing distance, the effect of the closer (opposite polarity) charges is greater and the two objects feel a force of attraction. Careful grounding of part of an object can permanently add or remove electrons, leaving the object with a global, permanent charge.

Removing or preventing a buildup of static charge can be as simple as opening a window or using a humidifier, to increase the moisture content of the air, making the atmosphere more conductive. Air ionizers can perform the same task.[2]

Items that are particularly sensitive to static discharge may be treated with the application of an antistatic agent, which adds a conducting surface layer that ensures any excess charge is evenly distributed. Fabric softeners and dryer sheets used in washing machines and clothes dryers are an example of an antistatic agent used to prevent and remove static cling.[3]

Many semiconductor devices used in electronics are particularly sensitive to static discharge. Conductive antistatic bags are commonly used to protect such components. People who work on circuits that contain these devices often ground themselves with a conductive antistatic strap.[4][5]

Within medical cable assemblies and lead wires, random triboelectric noise is generated when the various conductors, insulation, and fillers rub against each other as the cable is flexed during movement. Noise generated within a cable is often called handling noise or cable noise, but this type of unwanted signal is more accurately described as triboelectric noise. When measuring low-level signals, noise in cable or wire may present a problem. For example, the noise in an ECG or another medical signal may make accurate diagnosis difficult or even impossible. Keeping triboelectric noise at acceptable levels requires careful material selection, design, and processing as cable material is manufactured.[7]

The feeling of an electric shock is caused by the stimulation of nerves as the current flows through the human body. The energy stored as static electricity on an object varies depending on the size of the object and its capacitance, the voltage to which it is charged, and the dielectric constant of the surrounding medium. For modelling the effect of static discharge on sensitive electronic devices, a human being is represented as a capacitor of 100 picofarads, charged to a voltage of 4,000 to 35,000 volts. When touching an object this energy is discharged in less than a microsecond.[8] While the total energy is small, on the order of millijoules, it can still damage sensitive electronic devices. Larger objects will store more energy, which may be directly hazardous to human contact or which may give a spark that can ignite flammable gas or dust.

Lightning is a dramatic natural example of static discharge. While the details are unclear and remain a subject of debate, the initial charge separation is thought to be associated with contact between ice particles within storm clouds. In general, significant charge accumulations can only persist in regions of low electrical conductivity (very few charges free to move in the surroundings), hence the flow of neutralizing charges often results from neutral atoms and molecules in the air being torn apart to form separate positive and negative charges, which travel in opposite directions as an electric current, neutralizing the original accumulation of charge. The static charge in air typically breaks down in this way at around 10,000 volts per centimeter (10 kV/cm) depending on humidity.[9] The discharge superheats the surrounding air causing the bright flash, and produces a shock wave causing the booming sound. A lightning bolt is simply a scaled-up version of the sparks seen in more domestic occurrences of static discharge. The flash occurs because the air in the discharge channel is heated to such a high temperature that it emits light by incandescence. The clap of thunder is the result of the shock wave created as the superheated air expands.

Many semiconductor devices used in electronics are very sensitive to the presence of static electricity and can be damaged by a static discharge.The use of an antistatic strap is mandatory for researchers manipulating nanodevices.Further precautions can be taken by taking off shoes with thick rubber soles and permanently staying with a metallic ground.

The flowing movement of finely powdered substances or low conductivity fluids in pipes or through mechanical agitation can build up static electricity.[11]The flow of granules of material such as sand down a plastic chute can transfer charge, which can be measured using a multimeter connected to metal foil lining the chute at intervals, and can be roughly proportional to particulate flow.[12] Dust clouds of finely powdered substances can become combustible or explosive. When there is a static discharge in a dust or vapor cloud, explosions have occurred. Among the major industrial incidents that have occurred due to static discharge are the explosion of a grain silo in southwest France, a paint plant in Thailand, a factory making fiberglass moldings in Canada, a storage tank explosion in Glenpool, Oklahoma in 2003, and a portable tank filling operation and a tank farm in Des Moines, Iowa and Valley Center, Kansas in 2007.[13][14][15]

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