AQA Physics Electricity notes

ELECTRICITY
current and
charge
Electric current rate of flow of
is the
charge in a wire or
component

due to of metals ( collide with other and the fixed the metal )
charge conduction each
↳ carriers e- + ve ions in
passage
a :
.




salt solution : ions (
charged atoms or molecules )


Convention for direction of current to
negative
:

positive
current ( I ) force between two current
; ampere
(A) :

magnetic parallel wires when
they carry the same




(Q ); ( C)
charge coulomb :

charge flow in one second when the current is one
ampere .




C current A
charge , ,




Current of due to flow of second
IA
charge 1C
Q
is

It
a
•




per .




=


of 1.6 -19C current of IA due to
charge
↳ 1 e- 10 is
;
: ×



time ,
s

's
each
6. 25×10 e-
passing along a wire second 1 A =
1000mA




Insulator Semiconductor
number of temperature
each e- is attached to atom and cannot charge carriers increases with an increase in
•
.
an move




from the atom resistance of semiconductor decreases as
temperature increases
away
.




insulator A
through the
semiconducting material called intrinsic semiconductor
-




no e- can move no is an
pure
•
.
. .




from the atoms
current
passes through when
voltage is
applied .
↳ conduction is due to e- that break free .




Metallic conductor

most attached to but de localised these
. e- are atoms some are are the
charge carriers




conduction attracted towards terminal
• when
voltage is
applied ,
electrons are
positive


Potential difference and
power
Potential difference done ( or transfer )
is work
energy per
unit
charge voltage across the
component
volt V 1 coulomb work done J
=

joule per u
,



p.d.
,




W
,




V =


Q
charge ,
C




Electromotive force ( emf ) of of
electricity electrical unit
charge passing through the source
a source
energy per
:




Heating effect :
when electric current
passes through component with resistance


↳ also has
magnetic effect ( in electric motors and
loudspeakers )


power ,
W current A ,
work done ,
J voltage ,
V

time
P
S

VI W VIT
,

= =




V current A
voltage ,
.

, Resistance
resistance A V
,
voltage ,

of
a measure of
difficulty making current
pass through the
component ✓
•


.




R =


Resistance is
the
pd across the component T
current A
-



the current
through it ,




caused
↳
by the
repeated collisions between the
charge carriers in the material with each other and with the fixed


of the
positive ions material .




Ohm 's Law states that the
pd across a metallic conductor is
proportional to the current
through it
,




conditions do not
provided the
physical change .




voltage ,
V




treat
Unless
specifically stated in the
question
:

,




Ammeters 0 resistance
as
having
-




Voltmeters infinite resistance
as
having
-




0
current ,
I




Resistivity
'

, p resistance ( r )




①
resistance ,
A

resistance R
resistivity rm
RA
,
, '
cross-sectional area
,
m




P
=


L cross-sectional area A

length ,
m




"
1 " d
R ✗ L R ✗ A =
0
4
A length 1m )




Superconductor is a wire or device made of material that has 0
resistivity at and below a critical temperature

that
depends on the material




This
property is called
superconductivity .




↳ when a current
passes through it
,
there is no
p.d. across it because its resistance is 0 .




( accelerators )
Applications : used to make
high-power electromagnets to
generate very strong magnetic fields .
MRI scanners
, particle

:
reduction of
energy
loss in transmission of electric
power ( lightweight electric motors
, power
cables )




Measuring the variation of current with
p.d. for a
component :




divider ) variable resistor
i )
potential ii




current to




|
through and the
-




the
•
current the
component .
varies a minimum




pd across it can be reduced to 0 .
A ( cannot be reduced to 0 )


✗
A


I.
V


V