IB Physics 12 Mr. Jean November 20 th , 2013
IB Physics 12
Mr. JeanNovember 20th, 2013
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=Hvmke
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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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Resistors in Series• http://www.youtube.com/watch?v=yKbCS
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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