Notes: Electric Circuits Current, Voltage, Resistance, Ohm’s Law, and Power Physics 614

CURRENT ELECTRICITY CURRENT ELECTRICITY is the controlled movement or flow of electric charges along a conductor. An ELECTRIC CIRCUIT is a controlled path for the flow of electric current. There are 4 main components to most circuits: energy source, load, conducting wires, switch.

Electric Circuits

What Is Current? continuous flow of ________ through a material to produce current, charges must flow continuously in a __________, __________ path Symbol: ________ Unit: _________ (A or Amps) 1 A = 1 C/s electrons complete unbroken I Ampere Ammeter

Current Remember, the path that current flows through must be complete and unbroken. If there’s a break, the current will NOT flow! Bueno! No bueno.

What is voltage? Energy V Volts _____________ available to move charges through a circuit think of it as a force that pushes _________ through a circuit voltage is also called the “potential difference” because there is a difference between the potential energy of the electrons in the voltage source and the electrons in the current Symbol: ______ Unit: ___________ (V) charges V Volts

Voltage

Voltage voltage is created by a voltage source, such as a _______, generator, solar panel, or ____________ battery wall outlet

What is Resistance? describes how ________ it is for the electrons to flow through a material Conductors: ____ resistance, current flows ______ Insulators: _____ resistance, do not allow current to flow easily Symbol: ______ Units: ________(Ω) difficult low easily high R Ohms

Resistance All sorts of items have resistance: light bulbs, doorbells… basically, whatever is “using” the energy in the circuit!

Resistance There are four factors that affect the resistance of a wire: Length: the longer a wire is, the ________ resistance it has Diameter: the thicker a wire is, the _____ resistance it has Material: Wires made of poor conductors have _____ resistance than wires made of good conductors Temperature: As a wire gets hotter, its resistance _________. more less more increases

Resistors A resistor is a device that reduces/controls the flow of electric current.

Current, Voltage, and Resistance

Current, Voltage, and Resistance

Bigger Voltage = Bigger Current Voltage & Current Bigger Voltage = Bigger Current

Resistance Larger resistances need more voltage to have the same current

V = IR Ohm’s Law V = ________ (Volts) I = ________ (Amps) Voltage Current Resistance

Current Depends On Voltage and Resistance What happens to the amount of current if we increase the voltage? The current _________. increases

Current Depends On Voltage and Resistance What happens to the amount of current if we increase the resistance? The current __________. decreases

Ohms’s Law Practice A light bulb with a resistance of 5 ohms is connected to a battery. The current is 4 Amps. What is the voltage of the battery?

A 12 volt battery is connected to a circuit with a resistance of 4 ohms. What is the current?

A toaster is plugged into a wall outlet, such that V = 110 volts and I = 10 Amps. What is the toaster’s resistance?

Electric Power Review: Unit for power: ______ (W) Basically, a power rating tells you something about the rate at which electrical energy is being converted into some other form (thermal, light, mechanical, etc.) A 100 Watt light bulb is converting electrical energy into heat and light energy at a greater rate than a 40 Watt light bulb Watts

Electric Power: The Variables Use your MCAS FORMULA SHEET to determine what each symbol stands for *notice that it is a capital “P” and a capital “V” Symbol Term Units P Watts (W) I Amps (A) V Volts (V) Power Current Voltage

Electric Power: The Formula Find the formula that uses these three variables (P, I, V) P = IV Alternate: P = I V = I (IR) = I2R Twinkle, twinkle, little star, power equals I-squared-R

Electric Power Practice A motor connected to 120 V draws a current of 10 A. What power is being consumed?

A blow-dryer that uses 1800 Watts is connected to a 120 volt outlet A blow-dryer that uses 1800 Watts is connected to a 120 volt outlet. What current is passing through the blow dryer’s cord?

Series Circuits 13.1 - + In a series circuit, electrons flow through __________ _______. Loads are connected in a chain, one after another in one continuous loop. When one load does not work, the whole chain of loads ____________ because electrons ______ flow. only one path stops working cannot

Series Circuits 13.1

Series Circuits 13.1 The amount of current is the ________________ in a series circuit. same at all points

Parallel Circuits 13.1 In a parallel circuit, electrons can flow through _______________ path. Loads are connected in different branches that are connected to the energy source. When a load does not work in one branch, the loads in the other branches _________________ because electrons ________________ another path. more than one continue to function can flow through

Parallel Circuits 13.1

Parallel Circuits 13.1 Because there are multiple branches, the current is ___________________ in a parallel circuit. not the same at all points

Circuits and Safety: Short Circuits Short circuit: unintended direct contact between two points in an electrical circuit electricity always chooses the “path of ______ resistance” LOW resistance path = _____ current least high

Circuits and Safety: Short Circuits Short circuits could cause some problems Short circuits are dangerous because they can draw _____ amounts of current. Battery gets drained _______ Wire will ________, possibly melting the insulation, which could start a fire huge faster heat up

Circuits and Safety: Fuses Fuses prevent dangerous levels of ________ Short circuits and _________________________ can both cause high currents When the current is too high, the wire in the fuse melts the circuit is ________ the current can no longer flow the fuse must be _________ current plugging in too many items broken replaced

Circuits and Safety: Circuit Breakers Replacing fuses isn’t always the best solution Many homes/power strips have circuit breakers When the current is too high, the circuit breaker switch opens the circuit