IB Physics 12

Mr. Jean

November 7th, 2014

The plan:

• Video clip of the day

• Power

• Series Circuits

• Resistance in Series

• Application of Ohm’s Law

Resistance:

• http://www.youtube.com/watch?v=HvmkeERl65c

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 (m2). Thickness of the wire.

Example:

• Calculate the resistance of a 15 m length of copper wire with diameter of 0.05cm.

• Known Implied Unknown

Calculations:

Electrical POWERWe have already learned that POWER is the rate at which work

(energy) is done. Circuits that are a prime example of this as batteries only last for a certain amount of time AND we get charged an energy bill each month based on the amount of energy we used over the course of a month…aka POWER.

POWERIt is interesting to see how certain electrical

variables can be used to get POWER. Let’s take Voltage and Current for example.

Other useful power formulas

These formulas can also be used! They are simply derivations of the POWER formula with different versions of Ohm's law substituted in.

Ways to Wire CircuitsThere are 2 basic ways to wire a circuit. Keep in

mind that a resistor could be ANYTHING ( bulb, toaster, ceramic material…etc)

Series – One after anotherParallel – between a set of junctions and parallel to each other

Simple Circuit

When you are drawing a circuit it may be a wise thing to start by drawing the battery first, then follow along the loop (closed) starting with positive and drawing what you see.

Series Parallel

Series Circuit In a series circuit, the

resistors are wired one after another. Since they are all part of the SAME LOOP they each experience the SAME AMOUNT of current. In figure, however, you see that they all exist BETWEEN the terminals of the battery, meaning they SHARE the potential (voltage).

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Totalseries

Totalseries

Resistors in Series

• http://www.youtube.com/watch?v=yKbCSE7GGBQ

Circuits in Series:

• When a circuit is in series it means that each component has the same current.

Resistance in Series:

• Simply sum all resistance together. The total amount of the resistance is equal to the sum of all the resistance in the system.

• Req = R1 + R2 + … + Rn

Example question:• There are 4 resistors in series. They have

the resistance of 3.0Ω , 5.0Ω, 7.0Ω and 9.0Ω. The power supply is a 9.0V battery.

• 1) Draw the circuit with all resistance.

• 2) Draw the simplified circuit.

• 3) What is the total current in the system?

• 4) What is the potential difference across each individual resistor?

Simplifying Resistance in Series:

Vs = IsReq

• Use Ohm’s Law:

Potential difference across each:

• V1 = IsR1

• V2 = IsR2

• V3 = IsR3

• V4 = IsR4

To do:

• Work on Quest assignment

• Read about Topic #5

• Review circuit notation