Charging by friction

1
Teachers Notes This sequence of slides is
designed to introduce, and explain electrostatic
charging by friction, as explained on page 242
in New Physics for You, 2006 2011
editions(page 248 in Physics for You, 2001
edition). Note When you start this PowerPoint
if you see a message about Read-only embedded
fonts then you are recommended to select Open
Read-Only as this (i) gives a clearer font for
those at the back of the room and (ii) ensures
that the text-highlighting of key words is
correct. On each slide the key points are
revealed step by step, at the click of your
mouse (or the press of a key such as the
space-bar). Before making the next mouse-click
you can ask questions of the class or make
statements about what is about to be
revealed. This should help students to become
clearer about the ideas involved. Naturally it
pays to have quick practice-run first. To start
the slide-show, press function-key F5 (or
right-click-gtFull Screen)(to return to normal
view press the ltEscgt key). For more (free)
PowerPoint presentations, visit
www.physics4u.co.uk
2
Charging by friction
New Physics for You, page 242
3
Learning Objectives You should learn

• How insulated objects can be charged by friction,
• That this is because some charges can move.

4
Charging by friction
In this diagram
The wool and polythene are each uncharged. What
does this mean?
5
Charging by friction
- - -
The wool is uncharged,because it has equal
amounts of positive and negative charge. Equal
numbers of and - On the wool
- - - - - - -
On the polythene
6
Charging by friction
Equal numbers of and - on the wool
(Count them!) 7 7 -
Equal numbers of and - on the polythene
(Count them!) 3 3 -
7
Charging by friction
If you rub the wool on the polythene, some
electrons (-) move from the wool to the polythene.
There are now more than - on the wool
(Count them!)
So now the wool is charged positively, with a
surplus of 3
8
Charging by friction
What has happened to the polythene?
There are now more - than on the polythene
(Count them!)
So now the polythene is charged negatively, with
a surplus of 3 -
9
Charging by friction
This is summed up in the diagram on page 242
Both objects are now equally charged, with
opposite charges because electrons - (only) have
moved.
10
Learning Outcomes You should now

• Understand what it means when an object is
  charged or uncharged,
• Understand how an insulated object becomes
  charged by rubbing,
• Understand why the objects have equal but
  opposite charges,
• Know that only electrons (-) can move.

11

• For more details, see
• New Physics for You, page 242
• For more free PowerPoints, visit
• the web-site at www.physics4u.co.uk

12
If you are connected to the web at the moment,
click below to see whats available
http//www.physics4u.co.uk/
13
(No Transcript)
14
(No Transcript)