- I welcome your
questions and comments. -Charles Kim.
Email to me at firstname.lastname@example.org
The Laws of Circuit - you can learn and practice by just
copyright. Charles Kim 2006
- VOLTAGE DIVIDER RULE
- When a voltage is applied across the two
resistors connected in series, the voltages across each
resistor are dependent upon the values of the resistors.
You can say that the voltage is divided (or distributed)
into two resistors, and the sum of two voltages is the
same as the applied voltage. How much voltage is
developed across a resistor is what the voltage rule is
all about. What it says is the amount of the voltage (or
the portion of the applied voltage) developed across a
resistor is directly proportional to the value of the
resistor. After all according to the Ohm's Law, when
current is the same, voltage is proportional to
- If a resistor's value is 20% of the total
combined resistor, then the voltage across the resistor
is 20% of the applied voltage across the two resistors
connected in series. The other resistor's value is 80%
(100%-20%) and the voltage across the other resistor is
80% of the applied voltage.
- Consider a resistor of 20W and the
other resistor of 30W are serially connected and a voltage of 100V is
applied at the ends of the two serially connected
resistors. The voltage across 20W is then
[20/(20+30)]of the 100V, which is 40V. The voltage across
30W is [30/(20+30)] of 100V, which is 60V. So the
formula can be said: When a voltage is applied across the
two ends of the serially connected two resistors, the
voltage developed across a resistor is determined by the
portion of the applied voltage which is calculated by
dividing its resistance by the sum of its resistance and
the resistance of the other resistor.
- Warning: Apply this voltage divider rule
only when a voltage (whether a voltage source or
developed by other means) is applied to the ends of two
(or more) serially connected resistors.