Van de Graaff Generator

Robert J. Van de Graaff

Q1) How does it work?Q2) How does a Leyden jar store charge?Q3) How does a dead rabbit come back to life?

Electrostatics -

Atomic Structure Conductors Insulators

If a hydrogen atom was the size of Metlife Stadium, how big would the nucleus be?

Detecting Charge:

Charge Detecting Devices

Describe Rutherford's findings in his famous Gold Foil Experiment.

RULES

3 Methods of Charging

Separation of Charge Charging by Conduction Friction (CONTACT)

Outcome Outcome Outcome

Induction by Grounding (NO CONTACT)

Q1) How does it work?Q2) How does a Leyden jar store charge?Q3) How does a dead rabbit come back to life?

A Leyden jar, is a device that "stores" static electricity between two electrodes. It was the original form of a capacitor (originally known as a "condenser"). It was invented by German cleric Ewald Georg von Kleist on 11 October 1745 and by Dutch scientist Pieter van Musschenbroek of Leiden (Leyden) in 1745–1746. The invention was named for the city.

The Leyden jar was used to conduct many early experiments in electricity, and its discovery was of fundamental importance in the study of electricity. A famous use of the Leyden jar was Benjamin Franklin's kite experiment, which gave rise to the phrase "capture lightning in a bottle".

Units of Charge:

Negative Charge Positive Charge

• Elementary Particles (e) => Coulombs (C)

What is the charge in Coulombs for...

a) -6e

b) +3e

• Coulombs (C) => Elementary Particles (e)

How many extra/fewer e- does object have with charge of...

a) -3.2 X10-19C

b) 2.0 X10-19C

ELECTRON CANNOT BE CUT INTO PIECES!!

Conservation of Charge & Charge Transfer:

2 metal spheres touch then separate…

Total Charge =

A B

Total Charge =

A B

BEFORE

AFTER

a) What is the charge on each sphere after contact?

b) What subatomic particle(s) were transferred? From where to where?

c) How much charge did A gain in elementary particles and Coulombs?

d) How much charge did B lose in elementary particles and Coulombs?

What if?

MicroCoulomb (μC) :

a) How many elementary particles? b) How many MicroCoulombs?

-5 μC 3 x 1012e

Analogy: 325cents. How many Quarters?

Analogy: 636eggs. How many dozen?

Multistep Charge Transfer

1.

2.

3.

Net Charge = q 0 0

Net Charge =

Net Charge =

Two spheres have charges of +3µC and +7µC respectively...

a) What is the charge on each sphere after contact?

b) How much charge was transferred in..

i) µC

ii) C

iii) e

Δq= Δq=

Coulombs Law:

Two 1kg charged objects with charges of +2C and -4C are .5m apart…

a) What is the electrostatic force (Fe) between the objects?

b) What would be force if charges were +2C and +4C?

c) What is the gravitational force (Fg) between the objects?

Inverse Square Law Relationships

a) 4r

b) 2q1

c) 2q1, 3q2

d) 3q1, 3q2, 3r

Fe

Fe

Fe

Fe

Electric Field - E-Field Intensity/Strength

Electric Field Lines

Direction:

Rules:

E-Field vs. G-Field

a) What is the electric field strength if a point charge of 2C feels an attractive force of 10N?

b) Given the field strength in part ‘a’, how much force would a proton feels in this field?

c) If the sphere and the point charge are .1m apart, what must be the charge on the sphere?