Presentation on theme: "The study of electrical charges. Two possible states of charge: Positive and negative ▪ Named by Benjamin Franklin ▪ He decided what was considered."— Presentation transcript:
The study of electrical charges
Two possible states of charge: Positive and negative ▪ Named by Benjamin Franklin ▪ He decided what was considered “positive” and what was “negative” When 2 objects are rubbed together, one becomes “positive” and one becomes “negative”…electrons are transferred from one object to another. Flow of electrons = electricity
Insulators: materials that charges do not easily move through. Plastic, rubber, dry wood, glass Conductors: materials that allow charges to move. Examples: metals…copper, zinc, nickel, lead
Electric forces are the interaction of charged particles. Things to note: 2 kinds of electrical charge: positive and negative Charges exert force on other charges over a distance Like charges repel…opposite charges attract.
Charging a neutral body by touching it with a charged conductor. Electrons transfer to or from the conductor. The charge spreads throughout the neutral body.
A charged rod is held near a conductive material. Like charges repel, opposites attract. Material is grounded to allow transfer of electrons to earth. Ground then removed. Grounding: touching an object to Earth to eliminate excess charge. Lightning rods, grounding gas trucks, etc.
Charles Coulomb Worked with charged spheres to understand relationships between charge, distance, and force. Found that: ▪ F α 1/d 2 ▪ F α qq’ Coulomb’s Law K = 9.0 x 10 9 N*m 2 /C 2 q = charges (In Coulombs (C)) d = distance (meters)
1 Coulomb = the charge of 6.25x10 18 electrons 1 Electron = 1.6x C
Object A has a positive charge of 6.0x10 -6 C. Object B, carrying a positive charge of 3.0x C, is 0.03 m away. A. What is the force on A? B. What would be the force on A if the charge on B were negative?
Object A has a 6.0x10 -6 C charge and has 2 other charges nearby. Object B is 0.04 m to the right of A and has a charge of -3x10 -6 C and object C is 0.03 m directly below A and has a charge of 1.5x10 -6 C. What is the net force on A?
Concept of electric field developed by Michael Faraday A charge creates an electric field about it in all directions. A 2 nd charge inserted into the field interacts with the field at that point.
Only observed by measuring impact on other charged particles. A small positive test charge is placed a certain distance away
Electric fields are always considered using a small positive test charge Electric field lines show the direction of the electric field radiating from a charge. When considering electric fields produced from multiple charges, the field lines become curved and more complex.
The work done on moving a charged particle in an electric field can result in the particle gaining potential or kinetic energy. Pe electric = -qEd (in uniform electric field)
Electric potential increases as positive test charge is separated from negative charge Electric potential increases as positive test charge is moved toward positive charge.
Change in potential energy per unit charge Measured in J/C = V V = Volt ΔV = ΔPE/q’ Reference level for zero potential in a field is arbitrary
Only differences in electric potential are important Potential difference Measured with a voltmeter Often called “voltage” V = V B - V A
Uniform field can be produced by oppositely charged conducting parallel plates. ΔPE = +Fd V = +Fd/q = +(F/q)d E = F/q V = Ed
All systems reach equilibrium when energy is at a minimum. Charges on 2 objects try to spread out to reduce electrical potential. Grounding: touching an object to Earth to eliminate excess charge. Lightning rods, grounding gas trucks, etc.
Charges spread out as far apart as possible A Hollow conductor will have all charges on outside surface. ▪ Shields the inside from electric current ▪ People in a car with power lines across it.
Capacitance (C) = the ratio of charge to potential difference C = q/V Measured in farads (F)…1 F = 1C/V A device designed with a specific capacitance is a capacitor. Made of 2 conductors with equal and opposite charge separated by an insulator. Most capacitors are between 10 picofarads and 500 microfarads.