9/19 Lecture Chapter 21 Flashcards
Resistors in Series
When two or more resistors are connected end-to-end, they are said to
be in series
The current is the same in all resistors because any charge that flows
through one resistor flows through the other
The sum of the potential differences across the resistors is equal to the
total potential difference across the combination
Resistors in Series Equation for Potentials
ΔV = IR1 + IR2 = I (R1+R2)
Consequence of Conservation of Energy
Resistors in Series Equation
Req = R1 + R2 + R3 + …
Resistors in Parallel
The potential difference across each
resistor is the same because each is
connected directly across the battery
terminals
The current, I, that enters a point must
be equal to the total current leaving
that point
I = I1 + I2
The currents are generally not the same
Consequence of Conservation of Charge
Parallel vs Series Explain
Equivalent Resistance – Complex Circuit
Low resistance, thick wire
Quick quiz
Find the equivalent resistance
(b) 15 Ω
Combination of Light Bulbs
May have 2 filaments
Battery Pack Alignment
You normally group them together in a series to increase the voltage or in a parallel arrangement to increase the current.
Kirchhoff’s Rules
There are ways in which resistors can be connected so that the circuits formed cannot be reduced to a single equivalent resistor
Two rules, called Kirchhoff’s Rules can be used
instead
Junction Rule
The sum of the currents entering any junction must equal the sum of the currents leaving that junction
A statement of Conservation of Charge
Loop Rule
The sum of the potential differences across all the elements around any closed circuit loop must be zero
A statement of Conservation of Energy
Traveling around the loop from a to b (You have
to choose a direction for transversing the loop)
Junction Rule Equation
I1 = I2 + I3
Electrical Energy and Power
In a circuit, as a charge moves through
the battery, the electrical potential
energy of the system is increased by
ΔQΔV
The chemical potential energy of the
battery decreases by the same
amount
As the charge moves through a
resistor, it loses this potential energy
during collisions with atoms in the
resistor
The temperature of the resistor will
increase
Power = ?
Total Energy
