# Chapter 35: Electric Circuits

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Chapter 35: Electric Circuits
Conceptual Physics Bloom High School

35.1 A Battery & a Bulb Circuit- a complete path that the electrons take Electrons flow from the battery (dry cell) from the negative end and travel to the positive end Electrons are provided by the battery, wires, components Water as analogy Battery=pump Wires=pipe or hose Bulb=device that operates

35.2 Electric Circuits Switch- allows for a gap in a circuit
Gaps cause the electrons to stop flowing Turns the flow on and off Water analogy differences Closing a circuit = turn the flow on Opening a faucet = turning the flow on Wires can’t “leak” like a pipe or hose Series- devices that are connected in a row Allows for a single path for the electrons Parallel- devices are connected by their own ‘branch’ Allows for several paths an electron can take

35.3 Series Circuits Rules of Series Circuits
1. Current flows equally through each device. 2. The total resistance of the circuit is equal to the sum of the individual resistances. 3. The current is equal to the voltage of the source divided by the total resistance. (Ohm’s Law) 4. Ohm’s Law also applies to each individual device based on its resistance. 5. The total voltage of the circuit is equal to the sum of the individual voltage drops across each device.

Current flows equally through each device.

The total resistance of the circuit is equal to the sum of the individual resistances.
The total resistance of this circuit is 18kW.

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

Ohm’s Law also applies to each individual device based on its resistance.

The total voltage of the circuit is equal to the sum of the individual voltage drops across each device.

If one device fails, the whole circuit fails Old Christmas lights You don’t need to use everything to use one thing Microwave + Toaster + TV

Parallel Circuits Rules of Parallel Circuits
1. Each device connects the same two points of a circuit. The voltage is equal in each ‘branch.’ 2. The total current is divided among the branches. a. Path of least resistance is always taken. Current inversely proportional to resistance Ohm’s Law applies separately to each branch

Parallel Circuits Rules, part 2
3. The total current is equal to the sum of the currents. 4. As the number of branches increases, the overall resistance decreases. Overall resistance is less than the resistance of any one branch.

Each device connects the same two points of a circuit.

The total current is divided among the branches.

The total current is equal to the sum of the currents.
Physics Physlet P.30.2

As the number of branches increases, the overall resistance decreases.

35.5 Schematic Diagrams Schematic diagrams- uses symbols to represent parts of a circuit

35.6 Combining Resistors in a Compound Circuit
Is series, the resistances are added up In parallel, the addition is more complicated 1/R=1/R1+1/R2+1/R3… Add parallel resistances first Make the circuit appear to be series Add series resistances

Homes are fed with parallel circuits from utility companies More appliances added allows for lower resistance for the current Greater current can occur in the wires Overloaded- higher amount of current in wires than is safe Fire may result Short Circuit- a new, shorter path is offered and often bypasses regular resistance Fuses- rated to self-destruct (melt) at a certain current level (amperage) Circuit breakers- designed to turn off at a certain amperage

Circuit Breakers Increasing current boosts an electromagnets force.
When the current jumps to unsafe levels, the electromagnet pulls down a metal lever. The linkage tilts the moving contact away from the stationary contact to break the circuit.

Fuses Internal wire designed to melt at a prescribed amperage
In older homes, look like a light bulb base Most car fuses look similar to this Other types of fuses