Flashcards in Chapter 20 Deck (31):
Like charges do what?
Like charges repel each other
opposite charges do what?
opposite charges attract each other
what does neutral mean?
an object has no charge or the net charge is zero
what does charging mean (acquired charge)?
most things are electrically neutral, they have equal amounts of negative and positive charges. We can use certain materials to help them acquire charge. Most materials are divided into 3 categories
what are the 3 categories of materials used to charge objects?
1. Charging by Friction
2. Charging by Contact
3: Charging by Induction:
what is charging by friction?
this is useful for charging insulators, if you rub one material with another, electrons have a tendency to be transferred from one material to the other
what is charging by contact?
This is useful for charging metals and the conductors, If a charged object touches a conductor, some charge will be transferred between the object and the conductor, charging the conductor with the SAME sign as the charge on the object
what is charging by induction?
Also useful for charging metals and other conductors, a charge object is brought near/close to the conductor and does NOT touch iT, if the conductor is on the ground electrons will either flow away from it or onto it. when the ground connection is removed the conductor will have a charge OPPOSITE in sign to that of the object
what is electrical force?
the LONG-RANGE FORCE between charged objects, it can be repulsive or attractive
- gravity is another long-range force, but it is always attractive
what are the two types of electric charges that exist?
1. positive (proton)
2. negative (electron)
electric charge is always what?
electric charge is always conserved!
- objects become charged because negative charge is transferred from one object to another
what is nature's basic carrier of a positive charge?
- protons do not move from one material to another because they are held firmly in the nucleus
what is nature's basic carrier of the negative charge?
- gaining or losing electrons is how an object becomes charged
electric charge is?
electric charge is QUANTIZED: it comes in units of the fundamental charge
unit : Coulomb (C)
e = 1.6x10^-19 C
what is a conductor?
conductors are materials in which the electric charges move freely in response to an electric force.
- ie) metals; copper, aluminum and silver
- ADDED charge redistributes itself quickly over conductors
what is an insulator?
insulators are materials in which electric charges do not move freely.
- ie) plastics; glass, rubber
- when insulators are charged by rubbing, ONLY the rubbed area become charged, hey don't distribute themselves evenly
what is electrostatic equilibrium?
- charges on an insulator do not move
- charges on a conductor adjust until there is no net force on any charge
What is the Charge model?
The basic postulates of charges and charging
what does ground/grounded mean?
basically anything neutral that give up electrons to, or take electrons from, an object
what is Coulomb's Law?
The electric force between two point charges:
- is directed along the line joining the two particles
- is inversely proportional to the square of the separation distance (r) between them
- is proportional to the product of the magnitude of the charges |q1| & |q2| on the two particles
- is attractive if the charges are of opposite sign and repulsive if the charges have the same sign
K = 8.99x10^9 Nm^2/C^2
F2on1 = F1on2 = k|q1||q2|/r^2
Electrical force vs Gravitational force?
Electrical force is much stronger than gravitational force, which only has a G=10^-10 & K=10^+10
Fgravity = Gm1m2/r^2 = Felectric = K|q1||q2|/r^2
Vector Addition of Electric Forces?
The net force exerted on particle j is?
Fnetonj = F1onj + F2onj + F3onj.....
- Add vectors up by breaking them up into their components
what Is an Electric Field?
- The electric field at a point in space tells you how much force +1C charge would feel if it were placed at that point
- The electric field gives the force per unit charge
- The electric field is a vector quantity
- SI units of electric field are Newtons/Coulomb (N/C)
E = F/q = K|q|/r^2
what is the direction of an electric field?
The direction of the field is radially outward from a positive charge, or radially inwards towards a negative charge
What is the direction of an electric field between charged plates?
- The electric field points from the positive to the negative plate
- the field is uniform
E = Q/E0*A
what is an electric field like mea a continuous charge distribution?
- divide the total charge (Q) into (n) mini-segments with charge (ΔQ)
- treat each mini-segment as a point charge, and find the field due to each mini-segment
- add the fields due to each mini-segment, component by component
- The same becomes an integral as n->∞
what are electric field lines?
A convenient aid for visualizing electric field patters is to draw lines pointing in the direction of the field vector at any point
- the electric field is tangent to the electric field lines at each point
what are the electric field line patterns?
1. for a positive source charge, the lines radiate outward
2. for a negative source charge, the lines point inward
The high density of lines means what?
The high density of lines between the two charges indicates the strong electric field in this region
What is an electrocardiogram?
an electrocardiogram measures the changing field of the heart as it beats