Summary OCR A level Physics A 4.3 Electrical Circuits
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Course
Module 4: Electrons, waves and photons
Institution
OCR
Summary notes for topic 4.3 Electrical circuits including Kirchhoff’s Second Law, series and parallel circuits, internal resistance, potential divider circuits, combining resistors, and sensing circuits. Notes include definitions, highlighted key terms, diagrams, explanations and break downs of e...
In
any circuit , the sum
of the electromotive forces is equal
to the sum
of the
potential differences around a closed
loop .
Series Circuits
•
Only have one path for the current .
Current is the same in
every position
• .
•
e.
m.f.io shared between components .
components with equal resistances equally share e. m.fi
•
•
components with
larger resistances take
up a
greater proportion
of e. m -
f .
When there than
is more one source of e. m
f. check
•
-
,
POLARITY E. = 9. or Ei " "
e. { e. m f. 3 OV
o
g.
=
-
.
- -
- -
- -
NOT 15 OV
-
.
Parallel circuits .
•
More than one possible path for charges .
•
Amount of charge on each path depends on resistance .
Greater the resistance of lower the current
branch
passing
•
,
through .
Each parallel branch can be
thought of as a separate
•
circuit .
Branches are independent .
, The sum of the p d s
of the components on
any branch
• -
-
to the total e.m.fi
is
equal
Combining resistors
In series :
total resistance is proportional to the number
of resistors therefore total resistance ,
is the sum of the individual resistances
RER ,
+
Rzt .
.
.
In
parallel : as more resistors are added in parallel , resistance
drops .
Additional resistor provides another
path
current cross-sectional
for ,
increasing area
,
and so
lowering resistance .
¥ ¥ ¥
=
+ . . _
Internal Resistance
This
Work is done in the
that some
cell whenever a current
lost
passes
not all
'
' through it .
as heat and
means
energy is ,
energy
transferred
to the
charge is available
for the circuit .
As result the terminals the power
a ,
p.cl .
measured
of at
source (terminal p
-
d.) is lower than the actual em f- This .
difference is called lost volts .
lowers the terminal p d.
Increasing the current .
,
as it means
by the charges
more work is done in the cell
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