Conceptual Physics Notes on Chapter 35 Electric Circuits.

Conceptual PhysicsConceptual PhysicsNotes on Chapter 35Notes on Chapter 35

Electric Circuits

Electric CircuitsElectric Circuits Any path in which electrons flow Any path in which electrons flow

is a is a CircuitCircuit.. There can be There can be no no gapsgaps in the flow of electrons. in the flow of electrons.

Electric CircuitsElectric Circuits A gap in the A gap in the

circuit is known as circuit is known as an an Open CircuitOpen Circuit.. Electrons will not Electrons will not flow.flow.

A A Closed CircuitClosed Circuit is is when the flow of when the flow of electrons is electrons is possible.possible.

Electric CircuitsElectric Circuits Most circuits have more then one devise Most circuits have more then one devise

that receives electrical energy. These that receives electrical energy. These connections are in either:connections are in either:

SeriesSeries

ParallelParallel

Electric CircuitsElectric Circuits

SERIES CIRCUITSSERIES CIRCUITS:: Fig. 35.4 shows three lamps in series Fig. 35.4 shows three lamps in series

connected to a power supply --- a connected to a power supply --- a batterybattery..

1.1. Electric current has ONLY a single path Electric current has ONLY a single path through the circuit.through the circuit.

2.2. Resistance is the TOTAL resistance of each Resistance is the TOTAL resistance of each lamp or resistor along the pathwaylamp or resistor along the pathway..

3.3. The current is equal to the voltage source The current is equal to the voltage source divided by the total resistance (Ohm’s Law)divided by the total resistance (Ohm’s Law)

4.4. As the number of lamps is added, the As the number of lamps is added, the resistance is INCREASED.resistance is INCREASED.

The disadvantage of a series circuit is if one lamp fails (burns out) the whole circuit failsThe disadvantage of a series circuit is if one lamp fails (burns out) the whole circuit fails ..

Electric CircuitsElectric Circuits

PARALLEL CIRCUITSPARALLEL CIRCUITS:: Fig. 35.5 shows three lamps Fig. 35.5 shows three lamps

connected in parallel.connected in parallel.1.1. Each lamp connects the same two points. Each lamp connects the same two points.

Therefore, the voltage is the same across each Therefore, the voltage is the same across each device.device.

2.2. The amount of current in each lamp is the The amount of current in each lamp is the same.same.

3.3. Total current in the circuit equals the SUM of Total current in the circuit equals the SUM of the currents in each pathway.the currents in each pathway.

4.4. As the number of lamps is added, the As the number of lamps is added, the resistance is DECREASEDresistance is DECREASED..

Electric CircuitsElectric Circuits

SCHEMATIC SCHEMATIC DIAGRAMSDIAGRAMS::

• See Fig. 35.6 on page See Fig. 35.6 on page 554554..

Electric CircuitsElectric Circuits

BatteryBattery

SINGLE (Cell)SINGLE (Cell)

DOUBLEDOUBLE HIGHHIGH

(Battery) VOLTAGE(Battery) VOLTAGE

Electric CircuitsElectric Circuits

Connecting wire – Black lineConnecting wire – Black line

Electric CircuitsElectric Circuits

Open switchOpen switch

Electric CircuitsElectric Circuits

Closed switchClosed switch

Electric CircuitsElectric Circuits

Resistance Resistance

Electric CircuitsElectric Circuits

COMBINING RESISTORSCOMBINING RESISTORS::

Series and ParallelSeries and Parallel

See Fig. 35.8See Fig. 35.8

Electric CircuitsElectric Circuits When in series, the resistance When in series, the resistance

ADDSADDS up to a up to a larger resistancelarger resistance..

Very bright Bright DimmestVery bright Bright Dimmest

Electric CircuitsElectric Circuits When in Parallel, the resistance When in Parallel, the resistance

SUBTRACTS SUBTRACTS to a smaller to a smaller resistance.resistance.

Bright Same Bright Same BrightBright Same Bright Same Bright

Electric CircuitsElectric Circuits When lines carry too much current, When lines carry too much current,

the the heatheat may melt the wire and may melt the wire and start a fire.start a fire.

Fuses or Circuit breakersFuses or Circuit breakers are used to are used to prevent an overload in the wire.prevent an overload in the wire.