Chapter Six

1
Chapter Six
2
Objectives

• Midterm Review
• What is Electric Charge?
• Measuring Charge
• Force Fields
• What is Current?
• What is Magnetism?
• Magnetism and Electric Currents
• Electromagnetic Induction

3
What is Electric Charge?

• Joseph J. Thompson
• Charge
• Electron
• Nucleus proton stays fixed while electron orbits
• Types
• Positive positron e
• Negative electron e-
• A force between them
• Ions

4
What is Electric Charge? (cont.)

• Charge
• Electrostatic Charge
• Friction
• Contact
• Induction
• Conductors versus Insulators
• Semiconductors versus Superconductors

5
Measuring Charge

• 1 Coulomb 6.24 X 1018 electrons
• qne
• eq/n
• e1.60 X 10-19 C/e-
• Milliken Oil Drop Experiment
• Force
• Fkq1q2/r2
• k9 X 109 N m2/C2
• Creates fields

6
Force between electrons

• What is force of two electrons that are 2 cm
  apart?

7
Force between electrons in an atom.

• What is the force between an electron and proton
  in a Hydrogen atom where the first orbit is a
  distance of 5.29X10-11 m?

8
Force Fields

• Like gravitational fields
• Magnetic fields
• Positive to Negative
• We use a test charge to find the fields
• Model
• Action at a distance
• Field Model
• Field-Particle interaction
• Electric Potential
• P.D. W/q or 1 Volt 1 J/C

9
What is Current?

• A graphical example Water pump
• James Clerk Maxwell
• Electrical Circuits
• Voltage Source/Voltage Drop
• Current
• I q/t
• 1 Ampere 1 Coulomb/Second

10
Current (cont.)

• Related to current as in a river, it is called
  electric current
• Flows like a river
• Pushed at one end
• Flows at the speed of light
• Types
• Direct (flows one way)
• Alternating (flows both ways)

11
Current (cont.)

• Resistance
• A smaller stream off of the river (or smaller
  pipe). Less water flows.
• RPD/I RV/I VIR
• Ohms Law
• 1 Ohm 1 V/A
• Power
• W PD q
• P W/t PV q/t PVI

12
Resistance and Power of a Battery

• A voltmeter/ammeter measures the volts across a
  battery is 5 V and 4 mA. What is the resistance
  of the battery and power the battery produces?

13
What is the resistance and power across a
resistor?

• What is the resistance and the power across a
  resistor of which you read
• 7 V and 20 mA?

14
Magnetism

• Poles
• North
• South
• Magnetic Fields
• Source is a moving electron
• Permanent magnet
• Domain
• Earths Magnet field

15
Magnetism and Electric Currents

• Right Hand Rule
• Solenoid
• Electromagnets
• Galvanometers
• Thermostat
• Telephones
• Motors

16
Electromagnetic Inductors

• Generators
• Magnet and electric coils
• Creates motion of the particles
• Faraday effect
• Transformers
• From one current to another
• Primary coil to secondary coil
• Step-up versus Step-down

17
Electrical Generator

• Electric Motor

18
Transformers
19
Power Transformation

• How many loops do you need in the secondary coil
  to transform 12,000 V to 12 V (the volts needed
  for a hairdryer) if your primary coil has 10,000
  loops?

20
Power Transformation

• What is the number of loops in the secondary coil
  need to transform 12V to 24V (The power needed to
  run the same hairdryer in Europe) if the primary
  coil has 40 loops?

21
Homework 7

• Chapter Seven
• Questions for Thought
• 2, 6, 10
• Parallel Exercises B
• 2, 14