IB Physics 12

Mr. Jean

October 30th, 2014

The plan:

How to control electric potential:

• The wire serves as a sort of charge pipe through which charge can flow.

• Conventional View: Positive charges travel through the wire (pipe) to the negative plate.

• Electron Current Model: Negative charges travel through the wire (pipe) to the positive plate.

• Both the conventional & electron model have the same net change to the system.

Conventional vs. Electronic Current:

Conventional current flows from positive to negative.

Electronic current which is the flow of electrons flows from negative to positive. This is because on negative terminal, there are more electrons.

In the symbol for a battery, longer line shows positive terminal whereas shorter line represents the negative terminal.

The Flow of Current: We use for this class

• Electrons flow from the negative terminal to the positive terminal. – When electricity was first discovered they didn't really have

a way of telling which way it was flowing so they made a guess.

– As it turned out, the guess was wrong.

When an electron moves from one position to another it leaves a "hole" behind. Another electron flows in and fills this hole, leaving its own hole further down the line.

• So in practice although electricity can be considered as a stream of electrons flowing from negative to positive, it can be equally considered as a stream of "holes" flowing from positive to negative.

Create the following circuits:

• 1) Create a circuit that has a 9V battery with three resistors R1, R2, and R3.

• 2) Create a circuit with an AC power supply, a resistors, a lamp, another resistor, a heater, and a push button switch.

• 3) Create a circuit with a battery as the power supply, a resistor, On / Off switch, a capacitor, a diode, and another resistor.

• 1) Create a circuit that has a 9V battery with three resistors R1, R2, and R3.

• 2) Create a circuit with an AC power supply, a resistors, a lamp, another resistor, a heater, and a push button switch.

• 3) Create a circuit with a battery as the power supply, a resistor, On / Off switch, a capacitor, a diode, and another resistor.

Problems:

• 1) Draw a circuit diagram with three resistors, a battery as a power source and one push button switch.

• 2) Draw a circuit diagram with 4 resistors, 1 capacitor, an alternating (AC) power supply, with an led dipole controlling electric flow in the clock wise direction.

Electric Current:

• I = the current in Amperes (A)

• q = the amount of charge in Coulombs (C)

• ∆t = the change in time in seconds (s)

Note: One coulomb per second is equivalent to one ampere.

Example:• Our houses use 120 volt wiring. The

toaster uses 9.6A for a period of two and a half minutes to toast bread.

A) Find the amount of charge that passed through the toasters.

Example:• Our houses use 120 volt wiring. The

toaster uses 9.6A for a period of two and a half minutes to toast bread.

B) Find the amount of energy that the toaster converted into heat while toasting the bread.

Example:A) Find the amount of charge that passed

through the toasters.

A)

Example:B) Find the amount of energy that the

toaster converted into heat while toasting the bread.

B)

Finding the number of Electrons

Electric Circuits:

• To draw out each individual component would be quite time consuming; therefore the world of circuits essentially have their own language to indicate what these symbols are.

Electric Circuits:

• Like notation in physics, this is not one agreed upon universal set of symbols which are used for every drawing; however here is the system we’ll use to create circuits in IB.

Understanding Circuit Diagrams:

Important to Note:

• Remember that by definition “Current” is the flowing from positive to negative potential.

• Current uses the conventional flow which is a bit unfortunate because electron flow is from the negative terminal to positive terminal.

To do:

• Continue to work on Quest Assignment

• Continue to read through chapters 16-18