A circuit is simply a closed loop through which charges can continuously move.
The word circuit is from
the same base as the
word circle, which
describes how the electrons move
Requirements of a Circuit
There must be an energy supply capable doing work on charge to move it from a low potential energy to a high potential energy location. This establishes a potential difference (voltage) across the two ends of the external circuit.
There must be a closed
conducting loop in the circuit
which stretches from the
high potential, positive terminal
to the low potential, negative terminal.
An analogy to help you…
A circuit is like a rollercoaster
It is a complete loop
There is a place where energy is put in to increase potential energy (a battery in a circuit and the chain pulling up the hill in the rollercoaster)
The rollercoaster naturally flows downhill just like charge in a circuit naturally flows from high potential to low potential
The diagram at the right shows a light bulb connected to a 12-V car battery. The + and - terminals are shown.
As a + charge moves through the battery
from D to A, it ________ (gains, loses) electric potential.
As a + charge moves through the external
circuit from A to D, ________ (gains, loses)
Use >, <, and = signs to compare the electric potential (V) at the four points of the circuit.
VA ___ VB ____ VC ____ VD
Decide if each statement is true or false:
When an electrochemical cell no longer works, it is out of charge and must be recharged before it can be used again.
2. An electrochemical cell can be a source of charge in a circuit. The charge which flows through the circuit originates in the cell.
3. Charge becomes used up as it flows through a circuit. The amount of charge which exits a light bulb is less than the amount which enters the light bulb.
4. The local electrical utility company supplies millions and millions of electrons to our homes everyday.
All statements were FALSE!!
When a battery is “dead” it is out of energy required to push a charge from one terminal to another
This energy can be restored in some batteries with a reversible chemical reaction…so it is more like reenergizing than recharging your batteries
Batteries are the source of energy in a circuit, charges carry the energy
Charge is not used up in a circuit, energy is
Electrons are already in your home, the power company supplies the energy to these electrons
A circuit is a set of electrical components connected so they provide one or more complete paths for the movement of charges
A load is any component or group of components that dissipates energy
A simple circuit consists of a source of potential difference (electrical energy) and a load
Drawing Circuits with Schematic Diagrams
of an electric circuit
A light bulb contains
a complete conducting path
(regular and decorative lights)
A light bulb is considered
a load because it dissipates
electrical energy (by
converting it to light energy)
The energy per unit charge supplied by a source of electric current
Any device that increases the potential difference and energy of charges circulating in a circuit
Current flow shows
the direction of +
EMF shows the flow
Types of Circuits
Path from one terminal to the other is complete. A potential difference exists and electrons move from one terminal to the other.
No complete path. No charge flow and no current
Without a load the circuit contains little resistance to the movement of charges.
This causes high current which can damage circuit components.
Types of Circuits
A circuit or portion of a circuit
that provides a single conducting
path without junctions
A circuit or portion of a circuit in which two or more components are connected across a common point or junction, providing multiple conducting paths for the current
Resistors in Series
Resistors in series all have the same current
The total (or equivalent) resistance can by found by finding the sum of all resistors
R EQ = R 1 + R 2 + ….
A 9.0 V battery is connected in series to four resistors with values of 2.0 , 4.0 , 5.0 , and 7.0 . Find the equivalents resistance for the circuit and the current in the circuit.
Hint: Draw a diagram!
Answer: R= 18 and I=0.50A
Resistors in Parallel
Resistors in parallel have the same potential difference (voltage) across them.
The sum of the currents in parallel resistors equals the total current
Equivalent resistance is the sum of the reciprocals
1/R EQ = 1/R 1 + 1/R 2 + ….
A 9.0 V battery is connected to four resistors in parallel with values of 2.0 , 4.0 , 5.0 , and 7.0 . Find the equivalents resistance for the circuit and the current in the circuit.