Mr. Rogers' IB/AP Physics II: E&M Objectives

Syllabus 1st Quarter 2nd Quarter 3rd Quarter 4th Quarter IB Objectives

AP Physics C E&M Standards

A. Electrostatics .....................................................................30%

1. Charge, field, and potential
2. Coulomb's law and field and potential of point charges

3. Fields and potentials of other charge distributions

a. Planar
b. Spherical symmetry *
c. Cylindrical symmetry *

4. Gauss's law *

Chapter 23

Charge

Essential Question: How is charge similar and different than mass?

  1. Describe the nature of charge.
    • Like repel, opposites attract
    • Freely moves in conductors, not free in insulators
    • Conserved
    • Quantized
    • Analogous to mass in many equations
  1. Explain the difference in charging an object by induction and charging it by conduction.
  2. Calculate electrostatic forces using Coulomb's law.
    • One dimension
    • 2 Dimension
  1. For a hydrogen atom, calculate the ratio of electric to gravitational attraction forces.
  • G = 6.7 x 10-11 m3/ (kg * s2)
  • k = 9.0 x 109 N*m2/ C2)
  • mass electron = 9 x 10-31 kg
  • mass proton = 1.7 x 10-27 kg
  • charge proton = 1.6 x 10-19 C
  • charge electron = 1.6 x 10-19 C

 

Formative Assessment: Group and individual problem solving on white boards.

Homefun: prob 1, 7, 9, 11 p.674-5 Serway

 

 

Demo: Van de Graaff Generator

Using the Van de Graaff Generator, demonstrate:

  • The nature of charge (see objectives)
  • induction
  • conduction

If the Van de Graaff Generator creates a voltage of on the order of magnitude of 100,000 volts, why is it not deadly?

 

Calculations:

Imagine separating a mole of hydrogen gas so that the electrons are at the north pole and the protons at the South Pole. Find the electrostatic force compression force acting on the Earth. 

 

Mini-Lab Physics Investigation (Requires only Purpose, data, and conclusion)
Title Investigation of the Ionizing Effects of UV Radiation
Purpose Can shielding prevent unwanted electric fields from producing noise signals in wires?
Overview Charge the electroscope and measure the length of time it takes for the leaves to come back together (indicating that the charge has been drained from the electroscope). Repeat this process several times and calculate an average time.

Repeat the first step except this time shine a UV light on the leaves.

Note: do not look directly at the UV light.

Data, Calculations Calculate a % difference between the UV and non UV cases for the time it takes to drain the charge off the electroscope. Use the averages of each in the calculation.
Questions, Conclusions
  1. Explain why the UV light does or does not affect the length of time it takes to drain the charge off the electroscope.
  2. Could an electroscope be used for indicating the presents of ionizing radiation?
Resources/Materials: Electroscopes, stop watches, UV radiation source

 

 

AP Physics C E&M Standards

A. Electrostatics (continued).....................................................................30%

1. Charge, field, and potential
2. Coulomb's law and field and potential of point charges
3. Fields and potentials of other charge distributions

a. Planar
b. Spherical symmetry *
c. Cylindrical symmetry *

4. Gauss's law *

Electric Field

Essential Question: How is knowledge of electric fields useful?

  1. State the general convention for the type of charge used in defining electrical phenomena. positive charge
  2. Define electric field and note how its equation is analogous to g = F / m in mechanics.
    • Map of force on a + test charge
    • E-field is a vector
    • E ≡ F / q
  1. Draw the electric field lines ( E-field rays) around point charges.
  2. State the meaning of the arrows and the spacing between lines in an electric field diagram.
  • arrows: are rays indicating the direction of force on a hypothetical positive charge
  • spacing between lines: is proportional to e-field strength
  1. Use Coulomb's law to calculate the electric field around a point charge.
  2. Calculate the electric field:
  • along the axis through the center of a thin concentric charged ring radius = a -- model: ring of point charges

E = kQx / (a2 + x2)3/2

  • along the axis through the center of concentric charged disk of radius = R -- model: series of thin concentric rings

E = 2πkσ [ 1 - x / (R2 + x2)1/2 ]

  • infinitely large flat surface  -- model: disk with an infinite radius

E = 2πkσ

Geometry E-field Direction
point charge E =    (kQ) / (r2) radially outward from charge
infinite Line with uniform charge E =   (2kλ) / (r1) perpendicular to line
infinite plane with uniform charge E = (2πkσ) / (r0) perpendicular to plane

Formative Assessment: Group and individual problem solving on white boards.

Homefun: prob 15, 19, 23, 41, 43 p.675-6 Serway

Relevance: Electric fields are a basic principle in photocopiers, electrostatic precipitators, lighting rods, wireless communications, etc.

Video: Demonstration of Electrostatic Precipitators

Electrostatic precipitators are used for removing smoke, pollen, bacteria, or other particles from air. they charge the particles which are then attracted to oppositely charged plates.

Video--lab demo

Video--application

Question: Why would the electric field be particularly strong around a pointed electrode?

Answer: The charge on a conductive sphere will distribute equally & can be modeled as a point charge at the center. Hence, at the surface E = (kQ)/(R^2). As R approaches 0 (in other words becomes pointed), E approaches ∞.

Why are lightning rods generally pointed?

Video--lightning rod

 

 

Formal Physics Investigation

Title Millikan Oil-Drop Experiment
Purpose Determine the charge on an electron
Models Various
Overview Conduct the Millikan Oil-Drop Experiment according to the instruction sheet provided.
Safety Issues The experiment uses a high voltage source which can be a shock hazard
Equipment Limitations As always, the equipment is fragile.
Resources/Materials: Millikan Oil-Drop Experiment apparatus and high voltage power supply

 

 

Charged Particle Kinematics

Essential Question: How is the kinematics of charged particles used in TVs ?

  1. State the value of the e-field and force on a charged particle placed at any location above an infinitely large flat surface with a uniform charge.
  2. Solve kinematics problems for a charged particle in a uniform e-field.
  3. Solve projectile motion problems for a charged particle in a uniform e-field.
  4. Solve mechanical energy problems for a charged particle in a uniform e-field.

 

Formative Assessment: Group and individual problem solving on white boards.

Homefun: prob 37, 45, 51, 53

Relevance: Charged particle kinematics are a basic principle in CRT based TVs, x-ray tubes, and a host of electronic instruments such as oscilloscopes, mass spectrometers, etc.

Mini-Lab Physics Investigation (Requires only Purpose, data, and conclusion)
Title Beam strength vs. distance behavior of a microwave transmitter
Purpose Will a horn type microwave transmitter act like a point source and obey the inverse square law.
Overview

A horn type microwave transmitter is designed to transmit a beam of electromagnetic radiation. However, since microwaves can be modeled as a wave phenomenon they should tend to spread out as they propagate. at a sufficient distance the beam should spread out enough so that the microwaves' intensity begin to obey the inverse square relationship.

Place the microwave source on the floor and align it with the receiver at various distances across the room measure the relative beam intensity and draw a graph of relative intensity vs. distance.

Data, Calculations Perform linear and power regression analysis to determine if an inverse square law relationship exists in the data. Use residuals to gauge whether a given regression equation is appropriate.
Questions, Conclusions
  1. How can you test the receiver and transmitter for alignment?
  2. How does the electric field of the transmitter differ from the electric field of a point charge?
  3. Does the microwave transmitter create a magnetic field as well as an electric field?
Resources/Materials: Microwave transmitter and receiver.

 

SCALING FACTORS: THE FORM OF ANIMALS

Essential Question: Why is the design of an animal related not just to its function but also its size?

1) Describe 3 ways to characterize a "solid" object.

2) Define scale up factor (SUF). When an object is scaled up every dimension is multiplied by the same factor. This factor is called the scale up factor. An object scaled up in this manner will look the same as it's smaller version.

3) Develop a general scale up relationships for the 3 characteristics of solid objects.

4) Describe the key variable in an animal's weight and tell why it is not density.

5) State the key factor in a warm blooded animal's heat loss.

6) Describe the relationship between heat loss and food intake.

7) Describe the key factors in respiration.

8) State how the compressive strength of leg bones scales up.

9) State why animals can not be scaled up and down by large factors.

10) Analyze an animal's form using a knowledge of scale up factors.

 

Homefun: Work the Scale Up Factors Problems

Read: Insultingly Stupid Movie Physics
Chapter 4, Scaling: Big bugs and little people, pp 51 - 66

Relevance: Scale up is a major issue in virtually all design areas, pilot plant studies, or studies based on any type of scale model such as those used in wind tunnels.


AP Physics C E&M Standards

A. Electrostatics (continued).....................................................................30%


1. Charge, field, and potential
2. Coulomb's law and field and potential of point charges
3. Fields and potentials of other charge distributions

a. Planar
b. Spherical symmetry *
c. Cylindrical symmetry *

4. Gauss's law *

Chapter 24

Gauss's Law

Essential Question: Why is it sometimes necessary to shield against electric fields?

  1. Define electric flux--roughly speaking, the amount of electric field passing through a given surface.
  1. State the relationship between electric flux through a closed surface and the enclosed charge.

Gauss's Law:

Electric flux through a closed Gaussian surface is directly proportional to the enclosed charge (Q).  

Closed Gaussian surfaces are imaginary "bubbles" used for determining E-fields. The bubbles can be any shape including cubes, cylinders, or spheres as show above.

 

E da

= 4πkQ
    = Q /εo
 

where:

 
 

εo

= 1/(4πk)
    = permittivity of free space
    = 8.8542 x 10-19 C2/(N m2)

 

Homefun: Read 24.1 to 24.2

Questions 1-7 p.685; Problems 1, 3, 7 p. 686-687

 

Essential Question: How are gravity fields and electric fields similar?

E-Fields in and around: planes, non-conductive spheres, conductive spheres, and cylinders
  1. Solve for the electric flux created by a point charge through an infinitely large plane. ( E = 2πkQ )

  2. Solve for the electric flux created by a point charge next to finite sized plane. ( E = 2πkQ )

  3. Using Gauss's law derive the E-field around a point charge. ( E = kQ / r2 )

  4. Derive an expression for the electric field inside and outside a charged "fuzzy" sphere. ("fuzzy" sphere = uniformly charged non-conductive sphere)

  5. State the electric field inside a conductor in electrostatic equilibrium. (Hints: where does the charge go in a conductive object? Will there be any charge inside a Gaussian surface placed just inside of the object's surface?)

  6. Derive an expression for the E-field inside and outside a charged hollow conductive sphere. (Hint: how much charge is enclosed inside the hollow sphere?)

  7. Derive an expressions for the E-field inside and outside both very long fuzzy cylinders and conductive cylinders. (outside: E = (2kλ) / (r1))

 

Formative Assessment: Group and individual problem solving on white boards.

Homefun:

Read 24.3 to 24.4

Problems 11, 13, 15, 27, 45 pp. 687-688

Relevance: Gauss's Law is a powerful tool for calculating e-field strengths. This is an important issue in shielding from random electronic noise, antennae design, and wireless communication.

 

 

Essential Question: How are gravity fields and electric fields similar?

 
E-Fields in and around: planes, non-conductive spheres, conductive spheres, and cylinders
  1. Be as one with the info in table 24.1 p. 697.

  2. Be as one with the four magic box points on pages 693, 694.

  3. Derive an expressions for the E-field inside and outside both fuzzy and conductive concentric spherical shells.

  4. Derive an expressions for the E-field inside and outside both fuzzy and conductive inner spheres with concentric cylindrical outer shells. The outer surface of the outer shell acts like a point charge to the outside world. All the charges inside the outer shell are completely hidden or shielded from the outside world.

 

Charge sphere with outer shell

 

Formative Assessment: Group and individual problem solving on white boards.

Homefun: Problems 31, 39, 47 p. 688-689

Relevance: Note that the equation for e-field inside a non-conductive sphere with a uniform charge distribution (fuzzy sphere) is essentially identical to the derivation for the g-field inside a planet. We could create a Gauss's law of gravity.

 

Review of E-field Derivations Based on gauss's Law

Summative Assessment: Unit exam objectives 1-13

Demo: Shielding

  1. Turn on a transistor radio and place it a  atop a clean paint can lid.
  2. Slowly lower a clean empty paint can over the radio until the can contacts the lid.

Why does the radio lose its signal?

How is does the radio and can  demo different from the Gauss's Law analysis of shielding?

 
Investigation 1:  (Requires only Purpose, data, and conclusion)
Title Investigation of Shielding Effectiveness
Purpose Can shielding prevent unwanted electric fields from producing noise signals in wires?
Overview Wrap about 3 feet of unshielded single conductor wire into a coil about 10 inches in diameter. connect the two ends to an oscilloscope and place the coil atop a similar sized coil of an extension cord plugged into the wall. Observe the noise signal picked up by the single conductor wire.

Wrap an aluminum foil shield around the single conductor wire and connect one end of it to the oscilloscope's ground. Again observe the noise signal.

Data, Calculations Record your observations
Questions, Conclusions
  1. What does Gauss's Law indicate about the e-field inside a charged conductive surface in electrostatic equilibrium?
  2. How does the above situation relate to the conditions of the experiment? What is different?
Resources/Materials: Microwave transmitter and receiver.

 

 

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