PSC 4011 Electricity: What’s the connection?

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.

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.

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

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?

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).

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.

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.

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 (Coulomb’s law) ~ 1790_Galvani believes to have demonstrated that animals’ body is an organic Leyden jar 1800_Volta invents the first cell (birth of electrodynamics)

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!)

PSC 4011: Static Electricity & Magnetism Charging by friction:

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

PSC 4011: Static Electricity & Magnetism

Charging by induction:

PSC 4011: Static Electricity & Magnetism Charging by induction:

PSC 4011: Static Electricity & Magnetism Charging by induction:

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

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

PSC 4011: Static Electricity & Magnetism

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:

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 C)(5 x 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 / 1 x N F e = [(225)/1] x 10 [(-7)-(-4)] N F e = 225x N F e = N

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

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

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)

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

PSC 4011: Static Electricity & Magnetism Attraction Repulsion

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

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