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PSC 4011 Electricity: Whats the connection?

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PSC 4011: Static Electricity & Magnetism Electricity describes all of the phenomena caused by positive charges (protons) and negative charges (electrons) If a body (atom/molecule or object) has MORE PROTONS than electrons, it will be positively charged. If a body has MORE ELECTRONS than protons, it will be negatively charged.

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PSC 4011: Static Electricity & Magnetism Electrically charged objects, which have gained or lost ELECTRONS, tend to exert a force on other objects nearby. Like charges (+ + or - - ) will tend to REPEL each other. Opposite charges (+ - ) will tend to ATTRACT each other. Charges, are conserved.

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PSC 4011: Static Electricity & Magnetism When an object has the exact same number of protons and electrons it is called NEUTRAL. Charging an object consists in creating an imbalance in the electrical charge of that object. Materials can be divided in three groups, according to their reaction to the process of charging: Conductors Semiconductors Insulators

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PSC 4011: Static Electricity & Magnetism Every object fits somewhere along this conducting continuum Where do you think the human body would fit in the above diagram?

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PSC 4011: Static Electricity & Magnetism Conductors : permit the free flow of electrical charges. When charged, its electrons move in one general direction, pushing one another and making the charge move along the circuit. Metals and electrolytic solutions are conductors (ions).

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PSC 4011: Static Electricity & Magnetism Insulators: impede the free flow of electrical charges. When charged, its electrons are strongly held by the atomic nuclei, so charges do not move. Wood, glass, plastic, ceramics, paper, rubber, silk and air are also insulators.

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PSC 4011: Static Electricity & Magnetism Static electricity (electrostatics) describes all the phenomena related to electrical charges at rest. Charges are at rest when they are INSULATED. Static charge is often detected by a device known as an electroscope. There are three methods for charging objects.

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PSC 4011: Static Electricity & Magnetism DateEvent 6 th century BC_Thales discovers the electrical attraction of rubbed amber 1600_Gilbert discovers that many materials can be electrified _Bodies are divided into 2 categories: conductors & insulators _The human body is discovered to be a conductor 1746_Musschenbroek makes the first Leyden jar 1760_Franklin invents the lightning rod 1785_Coulomb establishes his law (Coulombs law) ~ 1790_Galvani believes to have demonstrated that animals body is an organic Leyden jar 1800_Volta invents the first cell (birth of electrodynamics)

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PSC 4011: Static Electricity & Magnetism Charging by friction: Two neutral bodies rubbed against each other. Some electrons are pulled from one of them. Resulting: two opposite charged bodies (attraction!)

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PSC 4011: Static Electricity & Magnetism Charging by friction:

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PSC 4011: Static Electricity & Magnetism Charging by conduction: Two solid bodies in contact with each other. The charge is transferred from the charged object to the second object. Resulting: two equally charged bodies, each with less charge than initially

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PSC 4011: Static Electricity & Magnetism

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Charging by induction:

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PSC 4011: Static Electricity & Magnetism Charging by induction:

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PSC 4011: Static Electricity & Magnetism Charging by induction:

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PSC 4011: Static Electricity & Magnetism Precautions (Static Electricity): Objects must be grounded in order to eliminate static charge built on them

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PSC 4011: Static Electricity & Magnetism Applications (Static Electricity): Objects are previously electrified, so their charge is kept, and attraction is guaranteed when in use

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PSC 4011: Static Electricity & Magnetism

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Example 1: For two positively charged particles, each with a charge of 5x10 -8 C and placed 1cm apart. Calculate the electrical force between the two particles:

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PSC 4011: Static Electricity & Magnetism F e = k(q 1 )(q 2 )/r 2 F e = (9 x 10 9 Nm 2 /C 2 )(5 x 10 -8 C)(5 x 10 -8 C)/(0.01m) 2 F e = (9 x 5 x 5) x 10 [9+(-8)+(-8)] / (0.0001) (Nm 2 /C 2 )(C)(C) / (m 2 ) F e = (225) x 10 -7 / 1 x 10 -4 N F e = [(225)/1] x 10 [(-7)-(-4)] N F e = 225x 10 -3 N F e = 0.225 N

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PSC 4011: Static Electricity & Magnetism Magnetism: Physical phenomenon produced by the motion of charge, resulting in attractive and repulsive forces between objects

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PSC 4011: Static Electricity & Magnetism DateEvent BC_Scientists observed an attraction between magnetite and iron 11 th century_Chinese and Arab sailors used compasses ~1270_Compass appears in Western Europe _Maricourt distinguishes North and South poles 1600_Gilbert fails to relate electricity and magnetism

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PSC 4011: Static Electricity & Magnetism Magnets: Objects upon which magnetism is observed. Magnets ALWAYS have two poles: North and South (if you break a magnet, you create two smaller magnets, each with its north and south poles)

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PSC 4011: Static Electricity & Magnetism Magnetic field: Magnetic influence of a magnet on its surroundings. Magnetic field lines: Representation of the magnetic field of a magnet. Lines exit North pole Lines enter South pole

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PSC 4011: Static Electricity & Magnetism Attraction Repulsion

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PSC 4011: Static Electricity & Magnetism Earth is a gigantic magnet

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PSC 4011: Static Electricity & Magnetism Electric forceMagnetic force _It acts on two types of charges (positive and negative) _Magnets have two types of poles (North and South) _Like charges: repulsion _Different charges: attraction _Like poles: repulsion _Different poles: attraction _Objects CAN have ONE type of charge (positively or negatively charged) _Magnets CANNOT have ONE type of pole (North or South) _It is inversely proportional to the square of the distance between the charges _It is inversely proportional to the square of the distance between the objects