Chapter 15 Flashcards
(16 cards)
What are the charges of electrons, protons, and neutrons using q?
qp=+e
qe=-e
qn=0
Can charge be created?
Not when two neutral objects run together (that’s cause electrons are transferred from one object to the other)
Charges can be created in some physical processes but in equal amount of positive and negative charge
(Conversation of charge)
What are conductors and insulators?
Conductors are materials in which electric charges move freely in response to an electric force (all other materials are insulators)
Metals are good conductors
Insulators are materials in which charge does not move easily
Glass, plastic, rubber, wood, paper are good insulators
What are semiconductors?
They have electrical properties between conductors and insulators
Silicon and germanium (semiconductors) electric properties can be adjusted by adding tiny amounts of impurities (phosphorus, gallium, indium, arsenic)
Semiconductors are used in electronic devices
What is charging by rubbing?
It is when different insulators are brought into contact and then separated, the insulators will have acquired a net electric charge of opposite polarity due to the transfer of electrons when bonds were formed when the objects were in contact
This charging effect can be enhanced by rubbing insulators together
Slide 13 Nov 5
What is the difference between charging by conduction and charging by induction?
Conduction- charged insulator is touched to a neutral conductor and gains a same polarity of charge as insulator and the amount of charge in the insulator (rod) will be reduced
Physical contact
Slide 15-18 nov 5
Induction- charged insulator is used to give a conductor a charge of opposite polarity and the amount of charge left on insulator (rod) is not changed (induction makes use of grounding)
No physical contact
Slide 21-26 Nov 5
What is grounding?
Examples of positive and negative rods touching ground?
A charged conductor can be discharged by connecting it to the Earth (grounding) (neutralizes object)
The earth is a conductor and can be thought of as limitless reservoir of charge
To ground a conductor means to provide a conducting path between it and the earth
Positive rod touch ground= electrons flow up and neutralize
Negative rod touch ground= electrons flow into ground and neutralize
What is polarization?
An electrically neutral object may have regions of positive and negative charge (charges can be separated)
The object is said to be polarized
Bits of paper can be polarized by induction
Water molecules are intrinsically polarized
Slide 28-29 Nov 5
What is Coulomb’s law?
Formula on formula sheet Electric forced between stationary charges are called electrostatic forces Moving charges create magnetic forces Like charges repel, opposites attract Slide 32 nov 5
Do example 15.3 on slides 5-8 Nov 7
Ok
What is the electric field?
What’s the trend with positive source charges and negative source charges
The independent presence of a charge at a point, it is a property of the other charges
Electric fields exist in a region of space around a charged object
Electric field exerts an electric force on any other charged object within the field
Positive source charges exert an electrical field away from them while negative source charges exert an electrical field towards them
Slide 13-15, 17-18 Nov 7
What are electrical field lines?
Can two field lines cross?
Where do they start and end?
Visualize electric field patterns
Electric field is strong when lines are closer together and weaker when they’re far apart
Direction of electric field at any point is tangent to the field like passing through that point
TWO FIELD LINES CANNOT CROSS
Field lines start on positive charges and end on negative charges
Slides 7-11 Nov 9
What are the properties of an isolated conductor? (4 of them)
- electric field is zero inside the conducting material
- any excess charge resides entirely on the conductors surface
- the electric field just outside a charged conductor is perpendicular to the surface
- excess charge accumulated at sharp points where the radius of curvature is smallest (used to be sharp ends but now found a bigger end works better maybe cause more surface area)
Slide 13 Nov 9
What are lightning rods?
Cause lightning to strike them rather than a building
Rod is connected to a conducting path to the ground so large current of lightning does not flow through building
They are pointed such that any excess/ induced charge on building resides on the tip of the rod which increases the chance lightning will strike
Blunted tip is better than a sharp one
What is faradays ice pail experiment?
Shows that any excess charge on a conductor resides entirely on its surface
Charge moves freely in a conductor
Some electrons in conductor are not bound to any atoms and thus are completely free to move within material
Slides 16-19 Nov 9
What is a Van de Graaff generator?
Slide 20 Nov 9 picture
Belt is neutral on the way up but becomes negatively charged when it rubs the upper roller which becomes positive charged, the + upper roller draws electrons from the dome which leaves the dome + charge and the roller neutral. Charge on dome is on exterior so electrons move from dome to upper roller as the belt moves, the electrons move from the belt to ground at the grounded lower roller
