transfer of charge
DESCRIPTION
This is a basic introduction to charging processes. It has some nice electroscope animations that I spent a lot of time creating. Please comment if you would like to see more of my physics PowerPoints - especially if you have specific requests!TRANSCRIPT
Mechanisms for Transfer of Charge
Restless Electrons
How do objects gain “static” charge?
• Friction– Rubbing two electrically neutral objects together can
charge both objects – both gain OPPOSITE charge
• Conduction– Charged object TOUCHES another object – electrons
jump from one to the other in an attempt to EQUALIZE the charge on both objects
• Induction– Charged object comes near another object WITHOUT
TOUCHING – causes it to POLARIZE
Conductive Properties of Solids
Conductors
allow charge toflow through them
easily
high conductivity
Insulators
inhibit chargeflow
high resistivity
rubber
silicon
wood
pure water
metals
special
metal alloys
SUPER CONDUCTORS SEMI INSULATORS CONDUCTORS CONDUCTORS
sea water
Friction
This works best when two INSULATORS are rubbedagainst one another
ConductionNegative To Neutral
--
Excess electrons exert repulsive forceson one another, causing them tomove apart as much as possible
BOTH now have the same charge!
ConductionPositive To Neutral
+ +
Electrons in the neutral object experiencean attractive force. They neutralize some of the
positive charge, leaving both with a lack ofelectrons
BOTH now have the same charge!
InductionNegative To Neutral
Polarization
+ -
-
Excess electrons exert forceagainst nearby electrons in the
neutral object
InductionPositive To Neutral
Polarization
+ -
+
Electrons in the neutral object experiencean attractive force, which pulls them
closer to the charged object
GroundingSince the Earth is so large it
can equalizecharges from other objects very easily
The Earth can equalize charge by:
absorbing excess electrons from
negatively charged objects
giving freeelectrons to positively
charged objects
In either case, grounding a
chargedobject makes it
neutral
One symbol that is often used to show thatsomething is grounded is:
Electroscope
- -
- -
- - -
An electroscope is a device thatdetects CHARGE
When the scope is CHARGED, theLEAVES at the bottom will REPEL one another
The charged LEAVESexert force on oneanother, forcing
them apart
Electroscope – negative cond.
- -
- -
- - - Step 1
Negative rod touchesneutral scope
Step 2
Electrons spread outand charge plates
Step 3
Scope is now negativelycharged
Step 4
Scope is grounded allowing electrons to
escape
Step 5
Scope is once againneutral – excess electrons
are gone
Electroscope – positive cond.
++
+ +
- - -
- -
-
Step 1
Positive rod touchesneutral scope
Step 2
Electrons leave scopebecause they are attracted
to the positive rod
Step 3
Scope is now positively charged
Step 4
Scope is grounded –electrons from the ground
are attracted to the positivescope
Step 5
Scope is once again neutral – balanced charge
is restored
Electroscope – negative ind.
- + - -
Step 1
Negative rod brought neargrounded scope
Step 2
Scope polarizes as electronsat the top try to move away
from the charged rod.
Step 3
Rod is removed – electronsare attracted back to the top
and “re-neutralize” theelectroscope.
Electroscope – positive induction
+
- -
Step 1
Positive rod is brought nearneutral electroscope
Step 2
Electrons from the bottomof the electroscope are
attracted to thepositive rod – get pulled up.
The leaves get a positivecharge on them.
Step 3
Rod is removed. Electronsare attracted back into the
leaves by the protons,making the electroscope
neutral again.
+ +
Electroscope – ind. with ground
- + -
++ - -
Step 1
Negative rod brought neargrounded scope
Step 2
Excess electrons from therod force electrons from the
scope into the ground.
Step 3
Ground is removed while the rod is still nearby, keepingelectrons from re-entering
the scope
Step 4
Scope now has a charge thatis opposite to the charge on
the rod
Step 5
The rod is taken away and thepositive charge remains
on the scope
Electroscope – ind. with ground
+
- - -
Step 1
Positive rod is brought neargrounded scope
Step 2
Electrons from the groundare attracted to the
positive rod
Step 3
Ground is removed, while therod is still nearby, pulling onelectrons and keeping them
from escaping
Step 4
Scope is now negatively charged – the opposite
charge as that of therod
Step 5
Rod is taken away and the negative charge remains
on the scope