Charge Introduction Section 0 Lecture 1 Slide 1 Lecture 28 Slide 1 INTRODUCTION TO Modern Physics...

Charge

Introduction Section 0 Lecture 1 Slide 1

Lecture 28 Slide 1

INTRODUCTION TO Modern Physics PHYX 2710

Fall 2004

Physics of Technology—PHYS 1800

Spring 2009

Physics of Technology

PHYS 1800

Lecture 28

Electricity and Charge

Charge


Lecture 28 Slide 2


Fall 2004


Spring 2009

UNIT THREEUNIT THREEElectricity and MagnetismElectricity and Magnetism

No area of physics has

had a greater impact on the

way we live than the study

of electricity and

magnetism.

Charge


Lecture 28 Slide 3


Fall 2004


Spring 2009

PHYSICS OF TECHNOLOGY Spring 2009 Assignment Sheet

*Homework Handout

PHYSICS OF TECHNOLOGY - PHYS 1800 ASSIGNMENT SHEET

Spring 2009 Date Day Lecture Chapter Homework Due Feb 16 17 18 19 20

M Tu W H F*

Presidents Day Angular Momentum (Virtual Monday) Review Test 2 Static Fluids, Pressure

No Class 8 5-8 5-8 9

-

Feb 23 25 27

M W F*

Flotation Fluids in Motion Temperature and Heat

9 9 10

6

Mar 2 4 6

M W F*

First Law of Thermodynamics Heat flow and Greenhouse Effect Climate Change

10 10 -

7

Mar 9-13 M-F Spring Break No Classes Mar 16 18 20

M W F*

Heat Engines Power and Refrigeration Electric Charge

11 11 12

8

Mar 23 25 26 27

M W H F*

Electric Fields and Electric Potential Review Test 3 Electric Circuits

12 13 9-12 13

-

Mar 30 Apr 1 3

M W F

Magnetic Force Review Electromagnets Motors and Generators

14 9-12 14

9

Apr 6 8 10

M W F*

Making Waves Sound Waves E-M Waves, Light and Color

15 15 16

10

Apr 13 15 17

M W F*

Mirrors and Reflections Refraction and Lenses Telescopes and Microscopes

17 17 17

11

Apr 20 22 24

M W F

Review Seeing Atoms The really BIG & the really small

1-17 18 (not on test) 21 (not on test)

No test week 12

May 1 F Final Exam: 09:30-11:20am * = Homework Handout

Charge


Lecture 28 Slide 4


Fall 2004


Spring 2009


PHYS 1800

Charge

Lecture 28

Electricity and Charge

Charge


Lecture 28 Slide 5


Fall 2004


Spring 2009

Describing Motion and Interactions

Position—where you are in space (L or meter)

Velocity—how fast position is changing with time (LT-1 or m/s)

Acceleration—how fast velocity is changing with time (LT-2 or m/s2)

Force— what is required to change to motion of a body (MLT-2 or kg-m/s2 or N)

Inertia (mass)— a measure of the force needed to change the motion of a body (M)

Energy—the potential for an object to do work. (ML2T-2 or kg m2/s2 or N-m or J)

Work is equal to the force applied times the distance moved. W = F dKinetic Energy is the energy associated with an object’s motion. KE=½ mv2

Potential Energy is the energy associated with an objects position.Gravitational potential energy PEgravity=mghSpring potential energy PEapring= -kx

Momentum— the potential of an object to induce motion in another object (MLT -1 or kg-m/s)

Angular Momentum and Rotational Energy— the equivalent constants of motion for rotation (MT-1 or kg/s) and (MLT-2 or kg m/s2 or N)

Pressure— force divided by the area over which the force is applied (ML -1T-1 or kg/m-s or N/m2 or Pa)

Charge


Lecture 28 Slide 6


Fall 2004


Spring 2009

What are the major subfields in Physics?

• Classical Physics (pre 20th century)• Mechanics → forces, motion

• Thermodynamics → heat, temperature

• Electricity and magnetism → charge, currents

• Optics → light, lenses, telescopes

• Modern Physics (20th century)• Atomic and nuclear → radioactivity, atomic power

• Quantum mechanics } → basic structure matter

• Particle physics

• Condensed matter → solids and liquids, computers, lasers

• Relativity, Cosmology → universe, life!

Charge


Lecture 28 Slide 7


Fall 2004


Spring 2009

State of Physics cira 1895

Electricity & MagnetismMaxwell Equations (c 1880)• Gauss’ Law•Faraday’s Law•Ampere’s Law•No magnetic monopoles

Mechanics (Gravity) Newton’s Laws (c 1640)1-Law of inertia2-F=ma3-Equal and opposite reactions

Conservation Laws• Energy• Linear & Angular Momentum

Statistical Mechanics• 3 Laws of Thermodynamics• Kinetic Theory

Charge


Lecture 28 Slide 8


Fall 2004


Spring 2009

Chapter 12Chapter 12Electrostatic PhenomenaElectrostatic Phenomena

Charge


Lecture 28 Slide 9


Fall 2004


Spring 2009

What does lightning have in

common...

... with hair on a dry winter day?

Charge


Lecture 28 Slide 10


Fall 2004


Spring 2009

Effects of Electric Charge

• Hair seems to have a mind of its own when combed on a dry winter day.

• What causes the hairs to repel one another?

• Why does a piece of plastic refuse to leave your hand after you peeled it off a package?

• Why do you get a slight shock after walking across carpet and touching a light switch?

Charge


Lecture 28 Slide 11


Fall 2004


Spring 2009

• All these phenomena involve different materials rubbing against one another.– Electrostatic effects can be demonstrated by rubbing plastic or

glass rods with different furs or fabrics.– Small wads of dry, paperlike material called pith balls are light

enough to be strongly influenced by electrostatic forces.– When a plastic rod, vigorously rubbed with cat fur, is brought

near the pith balls, at first the pith balls are attracted to the rod like bits of iron to a magnet.

– After contacting the rod, the pith balls dance away from the rod.

– They are now repelled by the rod and also by each other.


Charge


Lecture 28 Slide 12


Fall 2004


Spring 2009

• A repulsive force must be acting between the two pith balls after they have been in contact with the rod.– Perhaps the balls have received something (call it electric charge)

from the rod that is responsible for the force we observe.– This charge was somehow generated by rubbing the rod with the cat

fur.– The force that is exerted by one stationary charge on another is

called the electrostatic force.


Charge


Lecture 28 Slide 13


Fall 2004


Spring 2009

• Experiments with different materials indicate that there are two types of charge.

• An electroscope consists of two metallic-foil leaves suspended from a metal post inside a glass-walled container.– If the foil leaves are uncharged, they will hang straight down.– If a charged rod is brought in contact with the metal ball on top, the

leaves immediately spread apart and stay apart, even if the rod is removed.

– If an object of the same charge as the original rod is later brought near the metal ball, the leaves will spread farther apart.

– An object with the opposite charge will make the leaves come closer together.

– A larger charge produces a larger effect.

Like charges repel each other, and unlike charges attract

each other.


each other.

Charge


Lecture 28 Slide 14


Fall 2004


Spring 2009

• Benjamin Franklin introduced the names positive and negative for the two types of charge.

• He also proposed that a single fluid was being transferred from one object to another during charging.– A positive charge resulted from

a surplus of the fluid, and a negative charge resulted from a shortage of the fluid.

– Franklin arbitrarily proposedthat the charge on a glass rodwhen rubbed with silk be called positive.


each other.


each other.

Charge


Lecture 28 Slide 15


Fall 2004


Spring 2009

• Franklin’s model comes surprisingly close to our modern view.• When objects are rubbed together, electrons may be

transferred from one object to the other.– Electrons are small, negatively

charged particles present in all atoms and, therefore, in all materials.

– A negatively charged object has a surplus of electrons, and a positively charged object has a shortage of electrons.

– The atomic or chemical properties of materials dictate which way the electrons flow when objects are rubbed together.


each other.


each other.

Charge


Lecture 28 Slide 16


Fall 2004


Spring 2009

Conductors and Insulators

• Different materials behave differently in the presence of electrostatic forces.– Charge can readily flow through conductors:

• metals, like copper, silver, iron, gold; our bodies– Materials that do not ordinarily permit charge to flow are

insulators:• plastic; glass; ceramics; other nonmetallic materials

– Charge flows much more readily through several miles of copper wire than through the few inches of insulating ceramic material.

– Semiconductors are intermediate between a good conductor and a good insulator.

• Their importance to modern technology is enormous.

Charge


Lecture 28 Slide 17


Fall 2004


Spring 2009

Can you charge an object without actually touching it with another charged object?

• Charging by induction involves the conducting property of metals:– Charge a plastic rod with cat

fur and bring the rod near a metal ball mounted on an insulating post.

– The electrons in the metal ball are repelled by the negative rod.

– There is a negative charge buildup on the side opposite the rod, and a positive charge on the near side.

Charge


Lecture 28 Slide 18


Fall 2004


Spring 2009

Can you charge an object without actually touching it with another charged object?

• To charge the ball by induction, now touch the ball with your finger on the side opposite the rod.– The negative charge flows

from the ball to your body, since it is still repelled by the negative rod.

– If you now remove your finger and then the rod, a net positive charge is left on the ball.

Charge


Lecture 28 Slide 19


Fall 2004


Spring 2009

• Charging by induction illustrates the mobility of charges on a conducting object such as the metal ball.– The process will not work with a glass ball.

– Charging by induction is an important process in machines used for generating electrostatic charges, and in many other practical devices.

– It also explains some of the phenomena associated with lightning storms.

Charging By Induction

Charge


Lecture 28 Slide 20


Fall 2004


Spring 2009

Why are insulators attracted to charged objects?

• Recall that the pith balls were attracted to the charged rod before they were charged themselves.– Electrons are not free to move

in the insulating material of the pith balls.

– However, within each atom or molecule, charges can move.

– Each atom becomes an electric dipole: the center of the negative charge is slightly displaced from the center of the positive charge.

– The material is polarized.


Charge


Lecture 28 Slide 21


Fall 2004


Spring 2009

• Since the negatively charged surface is closer to the rod than the positively charged surface, it experiences a stronger electrostatic force.– The overall effect is that the pith ball is attracted to the

charged rod, even though the net (total) charge on the pith ball is zero.

– After the ball comes in contact with the charged rod, some of the charge on the rod is transferred to the pith ball.

– The pith ball is then positively charged like the rod, and so is repelled by the rod.


Charge


Lecture 28 Slide 22


Fall 2004


Spring 2009

• Polarization explains why small bits of paper or styrofoam are attracted to a charged object such as a sweater rubbed against some other material.

• Electrostatic precipitators used to remove particles from smoke in industrial smoke stacks use this property.– Polarized particles are attracted to charged plates in the

precipitator, removing them from the emitted gases.

Polarization

Charge


Lecture 28 Slide 23


Fall 2004


Spring 2009

Charging on the James Webb Space Telescope

Charging on the James Webb Space Telescope

Charge


Lecture 28 Slide 24


Fall 2004


Spring 2009


Next Lab/Demo: Electric Charge

Electric CircuitsThursday 1:30-2:45

ESLC 46 Ch 12 and 13

Next Class: Wednesday 10:30-11:20

BUS 318 roomRead Ch 13

Date post:	15-Dec-2015
Category:	Documents
Upload:	darnell-cowgill
View:	213 times
Download:	0 times

Charge Introduction Section 0 Lecture 1 Slide 1 Lecture 28 Slide 1 INTRODUCTION TO Modern Physics...

Documents