ELECTROSTATIC FIELDS & COULOMB’s LAW by Lizelle Swanepoel

ELECTROSTATICS

lizellexs — 2020-12-27 11:36:22 UTC

An object becomes electronically charged when the number of protons and electrons do not balance.
Static electricity results when this charge is isolated on an object by insulating material.
Excess electrons – object will be charged negatively.
Deficit of electrons – objects will be positively charged.
When one object is rubbed by another electrons are often transferred.
If one or both objects are insulators or insulated then static electricity results.

LAW OF CONSERVATION OF CHARGE

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Charge cannot be created nor destroyed but only transferred from one object to another.

ELECTRIC CHARGE

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INTRO PROBLEM

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CHARGE

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TRIBOELECTRIC SERIES

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DEVICES USED TO STUDY CHARGE

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Van de Graaff generator

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HOW THE VAN DE GRAAFF GENERATOR WORKS

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ROBERT VAN DE GRAAFF (1901 – 1967)

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He was a Dutch-American physicist, noted for his design and construction of high-voltage Van de Graaff generators.

Wimshurst machine

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PRINCIPLE OF CONSERVATION OF CHARGE

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The principle of conservation of charge states:
The net charge of an isolated system remains constant during any physical process (e.g. two charged objects making contact and separating).

CHARGE ON INSULATORS VS CONDUCTORS

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Metals are good conductors, so charge is free to move around in and on it.
Insulators (e.g. plastic and rubber) don't allow electric charges to move through them.

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REGULAR VS IRREGULAR SHAPED CONDUCTORS

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EVEN VS UNEVEN SPREAD OF CHARGE:

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THE CHARGE ON AN ELECTRON

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The elementary charge, usually denoted by e or sometimes q_e, is the electric charge carried by a single electron.

Elementary charge = charge on a single electron = -1,6 x 10^-19C.
Robert A. Millikan's oil drop experiment first measured the size of the elementary charge in 1909.

QUANTISATION OF CHARGE

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SHARING OF CHARGE

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PROBLEM: CHARGE ON CONDUCTING SPHERES AFTER TOUCHING AND SEPARATION

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CHARGING AN ELECTROSCOPE

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The grounding process involves:

A transfer of electrons between the charged electroscope and the conducting object to which it is touched.
When a negatively charged electroscope is touched, electrons exit the electroscope to the ground.
When a positively charged electroscope is touched, electrons enter the electroscope from the ground.

POLARIZATION OF CHARGE = process that induces electron movement or electron rearrangement

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POLARIZED WATER STREAM INTERACTS WITH CHARGED OBJECTS

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ELECTROSTATIC FORCE FALLS OFF WITH DISTANCE

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COULOMB'S LAW

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COULOMB'S LAW

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COULOMB'S EXPERIMENT

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NET FORCE BETWEEN THREE POINT CHARGES (co-linear)

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EXAMPLE 1:
The following three charges with distances apart are given:

Calculate the net force on q1

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Solution:

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3 POINT CHARGES AT A RIGHT ANGLE

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Calculate the net force on the red charge.

ANSWERS TO NOTES

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FIELDS QUESTION

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FIELDS MEMO

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ELECTROSTATIC VS GRAVITATIONAL FIELDS IN ACTION - BUILD YOUR OWN PARTICLE ACCELERATOR!

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EXERCISE 1 ANSWERS

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EXERCISE 1

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LET'S MARK EXERCISE 1

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Benjamin Franklin’s Leyden Jars

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ELECTRIC FIELD

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The electric field always runs perpendicular to the surface of any conductor.

ELECTRIC FIELD AROUND A CHARGE

lizellexs — 2022-09-21 12:19:01 UTC

DEF - Electric field:
A region of space in which an electric charge experiences a force. The direction of the electric field at a point is the direction that a positive test charge would move if
placed at that point.

Field direction:

AWAY FROM POSITIVE
TOWARDS NEGATIVE

FIELD BETWEEN CHARGES

lizellexs — 2022-09-21 12:27:21 UTC

Properties of electric field lines:

1. They start on positive charges and end on negative
charges.

2. They never cross.

3. They are 3-dimensional.

4. The denser the field lines the stronger the field.

5. They enter and leave charged object at right angles.

6. They are continuous (although drawn as separate lines).

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lizellexs — 2024-10-09 11:41:02 UTC

Dragging your feet on a carpet

lizellexs — 2025-09-18 12:11:36 UTC