Physics 12 Mr. Jean November 18 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

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.

Example: What is the resistance if a battery with 9.0V of potential difference causes a current of 0.45A to pass through a resistor?

Circuits in Series: When a circuit is in series it means that each component has the same current. For this example the battery voltage is divided between the two lamps. Each lamp will have half the battery voltage if the lamps are identical.

Christmas Lights: When several lamps are connected in series they will all be switched on and off together by a switch connected anywhere in the circuit. If one lamp blows all the lamps will go out because the circuit is broken. –If there are 20 lamps and the voltage is 240V, each lamp must be suitable for a 12V supply because the 240V is divided equally between the 20 lamps: 240V ÷ 20 = 12V.

Circuits in Parallel A circuit in parallel means that each component has the same voltage. In this example both lamps have the full battery voltage across them; however the current is divided between the two lamps.