Electric Circuits

4/27/15

Key Terms

Charge (q): The fundamental property of attraction / repulsion of electrons and protons. Unit is coulomb (C)

Current (I): The flow of electrical charge. Unit is amperes (A)

Key Terms

Voltage (V): The electric potential energy of a circuit. Unit is volts (V)

Conservation of Charge: The net electric charge is neither created or destroyed but can be transferred

Key Terms

Resistance (R): The difficulty of a charges to flow through a circuit element. Unit is Ohms (Ω)

Resistivity (ρ): A property of a material that allows or impedes the flow of charge. Unit is Ohm meter (Ω•m)

Key Terms

Conductors: A material (like metal) through which electric charge can flow

Insulators: A material where electric cannot flow freely

Key Terms

Series Circuit: Resistors connected in a single path

Parallel Circuit: Resistors are connected to the same two points of a circuit, so that any single resistor completes the circuit independently

Conditions for a Circuit

There must be a closed conducting path that extends from the positive terminal to the negative terminal.

There must be an electric potential difference across the two ends of the circuit.

Voltage Sources

Do work on each charge it encountersWhich transfers into electric potential

energy

The Battery

A negative charge will gain potential energy and voltage as it moves from positive terminal to negative terminal in the battery

The Circuit

A negative charge will lose potential energy and voltage as it moves from negative terminal to positive terminal in the circuit

Battery and Circuits

A negative charge has the least amount potential energy at positive terminal

A negative charge has the greatest amount potential energy at negative terminal

Voltage = Potential Difference

High PE

Low PE

Ohm’s Law

Ohm's law: states that the current through a conductor between two points is directly proportional to the potential difference across the two points (linear relationship)

Ohm’s Law

Current as a Water Slide

Voltage source = The water pumpVoltage (voltage difference) = Height of

the slidePositive terminal = Bottom of the slideNegative terminal = Top of the slide

Current as a Water Slide

Current = Rate at which water is flowingCharge = The waterResistors (electric device) = The poolOn/Off Button = Power switch

Waterslide vs. Circuit

Kirchoff Junction Rule

At any node (junction) in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node

i2 + i3 = i1 + i4

Kirchoff Loop Rule

The directed sum of the electrical potential differences (voltage) around any closed network is zero

The energy of circuit has to obey the conservation of energy

Kirchoff Loop Rule

v1 + v2 + v3 - v4 = 0

Voltage Source Examples

Voltage Sources Examples

Ex 1) Low voltage and low currentD-Cell battery: 1.5 V and 0.1 ALow waterfall with only trickle of water

flowing

Voltage Sources Examples

Ex 2) High voltage and high currentPower lines: 50,000 volts

and 65 AHigh waterfall with a river

of water flowing over it

Voltage Sources Examples

Ex 3) High voltage and low current:Electric fence: 6000 V and 0.1 A High waterfall with only trickle of water

flowing

Voltage Sources Examples

Ex 4) Low voltage and high current:Car battery: 12 V and 30 ALow waterfall with a gushing river of

water flowing

True or False Revisited

1. When a battery no longer works, it is out of charge.

2. A battery can be a source of charge in a circuit. The charge which flows through the circuit originates in the battery.

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.

True or False Revisited

4. Charge flows through circuits at very high speeds. This explains why the light bulb turns on immediately after the wall switch is flipped.

5. The local electrical utility company supplies millions and millions of electrons to our homes everyday.

6. High voltage circuit means there is a large current.

Quiz Tomorrow

Electrostatic WS Circuit WS (#1-3)

Ohm’s Law

Ohm's law: states that the current through a conductor between two points is directly proportional to the potential difference across the two points (linear relationship)

Ohm’s Law

Circuit Equations

I = Δq / Δt (Electric Current)R = ρ l / A (Electric Resistance)I = ΔV / R (Ohm’s Law)P = I ΔV (Electric Power)

Kirchoff Junction Rule

At any node (junction) in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node

i2 + i3 = i1 + i4

Kirchoff Loop Rule

The directed sum of the electrical potential differences (voltage) around any closed network is zero

The energy of circuit has to obey the conservation of energy

v1 + v2 + v3 - v4 = 0

Schematic Symbols

• Wires:• Resistor (elec. device):• Switch:• Battery:• Fuse: • Connected wires:• Unconnected wires

Schematic Symbols

• Wires:• Resistor (elec. device):• Switch:• Battery (Outlet):• Fuse: • Connected wires:• Unconnected wires