Physics 12 Mr. Jean November 17 th, 2011

The plan: Video clip of the day Van de Graff Generator Notes on field lines which were missed Electric Circuits –Symbols The good, the bad and the ugly of circuits

Van de Graff Generator:

Unbalanced Charges and Fields: Let’s say that we have two positive charges with one being stronger than the other.

Unbalanced Charges and Fields: Let’s say that we have two negative charges with one being stronger than the other.

Unbalanced Charges and Fields: Let’s say that we have two charges. A weak positive charge and a stronger negative charge.

Unbalanced Charges and Fields: Let’s say that we have two charges a strong positive charge and a weaker negative charge.

Key points to field diagrams: Electric field lines always extend from a positively charged object to a negatively charged object, from a positively charged object to infinity, or from infinity to a negatively charged object. Electric field lines never cross each other. Electric field lines are most dense around objects with the greatest amount of charge. At locations where electric field lines meet the surface of an object, the lines are perpendicular to the surface.

Key points to circuit diagram: Circuit diagrams show the connections as clearly as possible with all wires drawn neatly as straight lines. The actual layout of the components is usually quite different from the circuit diagram and this can be confusing. The secret is to concentrate on the connections, not the actual positions of components.

Purpose: A circuit diagram is useful when testing a circuit and for understanding how it works. This is similar to a force diagram for understanding dynamics.

Additional Useful Keys for Success: Make sure you use the correct symbol for each component. Draw connecting wires as straight lines. Put a 'blob' ( ) at each junction between wires. Label components such as resistors and capacitors with their values listed along side or below the circuit. The positive (+) supply should be at the top and the negative (-) supply at the bottom.

How to control electric potential: The wire serves as a sort of charge pipe through which charge can flow. Positive charges travel through the wire (pipe) to the negative plate.

To be a true circuit: To be considered a true circuit, charges must continually flow through a complete loop, returning to their original position and cycling through again. If there was a means of moving positive charge from the negative plate back up onto the positive plate, then the movement of positive charge downward through the charge pipe would occur continuously.

This is an example of a light and how it works in a circuit.

How to draw circuits: 1)Start at the source of potential energy. 2)Draw the circuit from positive (+) terminal to negative (-). 3)Electric Current (I) travels from positive to negative terminal. 4)Label component in the order in which they appear dictated by the electric current (I)

How to draw circuits:

Create the following circuits: 1) Create a circuit that has a 9V battery with three resistors R 1, R 2, and R 3. 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.

Exchange Diagrams Have your neighbour examine your diagram. –Questions to consider. Does the diagram includes all of the necessary pieces? Does the diagram clearly indicate what is going on? Could you use this diagram to create the circuit above given the components in a lab?

Return diagram to neighbour: To do: –Respond to the questions to consider 1) Give your neighbour constructive feedback and indication of how they are doing with their diagrams. 2) Think of ways their diagrams can be improved 3) Think of things which you will take from their diagram to improve your future drawings.

Diagram #1

Diagram #2

Diagram #3

Resistance of a Conductor: (Through a wire) R = resistance in Ohms (Ω) p = factor of resistivity in Ohms metre (Ω*m) L = length of the conductor in metres (m) A = cross sectional area of the wire metres squared (m 2 ). Thickness of the wire.

Example: Calculate the resistance of a 15 m length of copper wire with diameter of 0.05cm. KnownImpliedUnknown

Calculations:

Ohm’s Law: V = IR V = Potential difference in volts (v) I = Electric current in amperes (I) R = Resistance in ohms (Ω) 1A * 1Ω = 1V

Unit of resistance: One ohm is defined as the amount of electric resistance that will allow one ampere of current to move through the resistor when a potential difference of one volt is applied across the resistor.

Remaining time: 1) Work on projects –Rube Goldberg project –Book review –Presentation