Download pot. dividers

What we will do today
• Introduce potential divider circuits.
• Devise a formula comparing
resistances and voltages in potential
divider circuit.
Potential Dividers (Discussion)
•
A potential divider circuit is a series
circuit where the voltage (potential)
is split between two resistors.
•
What will our circuit diagram look
like?
Draw the circuit diagram in your
class jotter.
•
Potential Dividers
• A potential divider circuit is a series circuit
where the voltage (potential) is split
between two resistors.
• It is also known as a voltage divider.
• It is often shown on its side:
Potential Dividers
• From the equation for Vs in a series circuit
we know that Vs = V1 + V2
• Therefore there is a voltage drop across
each component in a series circuit.
• We can calculate these potential
differences using a voltmeter.
• However we can also calculate these values
when their resistance is known.
Experiment
• Connect two resistors in series to a
battery.
• Record the resistance of each resistor.
• Measure the voltage of the battery.
• Measure the voltage of each resistor.
• Fill in the table on the next slide.
Results
R1 ()
R2 () R1
R2
V1 (V)
V2 (V)
V1
V2
Conclusion
•
•
We can see that the ratio R1 / R2 is
the same as V1 / V2.
R1
V1
=
R2
V2
A potential divider circuit consists
of a supply voltage and two resistors
in series which divide the supply
voltage between them.
What we have learned
• For two resistors in series, we have
the ratio
R1
=
V1
R2
V2
• Using this ratio we can now work out
the p.d. across components when
knowing their resistances.
Example 1
•
•
•
•
R1
R2
V1
V2
=
=
=
=
?
200 Ω
1.5 V
3 V
• R1 =
R2
R1 =
200
R1 =
R1 =
V1
V2
1.5
3
1.5 x 200
3
100 Ω
What if you’re asked about R2 or V2?
• If asked about these values (the
denominators) then simply flip both sides
of the equation. So:
R1
=
V1
R2
V2
• Becomes:
R2
=
V2
R1
V1
• Then input values as in example 1
Example 2
•
•
•
•
R1
R2
V1
V2
=
=
=
=
100 Ω
200 Ω
2 V
?
• R1 =
V1
R2
V2
R2 =
V2
R1
V1
200
=
100
200 x 2 =
100
V2 = 4V
V2
2
V2
2009 Qu: 10
• E