Download Parallel Circuit

Bell Ringer:
• Define to the best of your ability the definition of:
• Current
• Voltage
• Resistance
• Explain the behavior of the current and the voltage in a Series Circuit.
• Explain the behavior of the current and the voltage in a Parallel Circuit.
Notes 8.4:
Parallel Circuits
This lesson promises to be
ELECTRIFYING!
Learning on Your Own:
• Active Physics – Chapter 5, Section 3, Page 617 – Series & Parallel
- Chapter 5, Section 6, Page 646 – V, I, R in Series & Parallel
• Physics (Red Book) – Chapter 23, Page 616 – Series & Parallel Circuits
• Instructional Videos:
https://www.youtube.com/watch?v=x2EuYqj_0Uk
Lesson Objective:
• Describe parallel circuits.
• Understand the wiring of a circuit connected in parallel.
• Define Kirchhoff’s Circuit Laws
• Calculate currents, voltage drops, and equivalent resistances in parallel
circuits.
Parallel Circuit:
• Which circuit is connected in series and which is connected in parallel?
• Try to draw a circuit diagram with each.
Parallel Circuit:
Parallel Circuit - Current:
• A parallel circuit is defined as one having more than one current path
connected to a common voltage source.
• Unlike in a series circuit, the current in a parallel current is subject to
change as it branches out.
• Kirchhoff’s Junction Rule (or Current Law):
The sum of the current entering any junction must be equal to the sum
of the current leaving that junction.
Parallel Circuit - Current:
• The algebraic sum of the currents entering and leaving any junction of
conductors is equal to zero.
𝐼𝑎 + 𝐼𝑏 + ⋯ + 𝐼𝑛 = 0
• NOTE: Currents entering the junction are assumed to be positive, and
currents leaving the junction are considered negative.
Parallel Circuit - Current:
𝐼𝑇 = 𝐼1 + 𝐼2 + ⋯ + 𝐼𝑛
Parallel Circuit – Voltage / Electric Potential Difference:
• In a parallel circuit, the same voltage is present across all the resistors
of a parallel group.
• NOTE: You can still use the Loop Rule.
Parallel Circuit – Resistance:
• Resistances connected in parallel can be replaced with an equivalent
resistance 𝑅𝑒𝑞 that has the same potential difference V and the same
total current I as the actual resistances.
1
1
1
1
=
+
+
𝑅𝑒𝑞 𝑅1 𝑅2 𝑅3
• NOTE: In parallel circuits the equivalent resistance will always be
smaller than the resistance of any branch.
Parallel Circuit – Resistance:
Parallel Circuit – Equivalent Resistance Example:
Given that 𝑅1 = 3 Ω, 𝑅2 = 6 Ω, and 𝐸𝑎 = 30 𝑉. Find the equivalent
resistance.
Check-Point I:
1. State the rule for current in a parallel circuit.
2. State the behavior of voltage in a parallel circuit.
3. State the behavior of a resistor in a parallel circuit.
(Continue on next Slide)
Circuit Terminology – Open Circuits (in Parallel):
• When comparing the effects of an open in series and parallel circuits,
the major difference to be noted is that an open in a parallel circuit
would not necessarily disable the entire circuit i.e. the current flow
would not be reduced to zero, unless the open condition existed at some
point electrically common to all other parts of the circuit.
Circuit Terminology – Short Circuits (in Parallel):
• A short circuit in a parallel network has an effect similar to a short in a
series circuit. In general, the short will cause an increase in current and
the possibility of component damage regardless of the type of circuit
involved.
NOTE: Opens and shorts, alike, if occurring in a branch circuit of a
parallel network, will result in an overall change in the equivalent
resistance.
Multiloop Circuits:
Multiloop Circuits:
Determine current 𝐼1 and 𝐼2 in the circuit below: