Current Flow (10/07/14)

During this class period, we went over current flow, and more on electromagnetism

Lighting A Bulb

A successful light bulb lit

We first watched a video on students trying to light a bulb with nothing more than a battery, a piece of wire, and of course a light bulb, then were asked to attempt the experiments ourselves
After a few tries, we learned the best way to light a bulb was to have both sides of the wire in contact with the battery and the bulb touching one of these wires would allow the bulb to light up
(It is to note to be careful about the wiring, if placed incorrectly, the wire heats up quickly and burns, as I personally experienced.



Afterwards, we were asked to answer the following questions for modeling a simple electric circuit
1) What does a battery give to a bulb? That is, what role does the battery play in the circuit?
2) What is getting “used up” in the bulb?

3) Why do you need a wire to go back from the bulb to the battery?

Our answer to those three questions

Below are videos that were taking after the Lighting a Bulb experiment, using a device that is able to react to electric fields

 The Concept of Electric Potential Difference
In order to get a better understanding of potential difference in electricity, we were asked a Physics 4A question regarding waterfalls and generator, and asked how big a generator has to be in order produce electricity, which requires two things about the waterfall itself.

Our response to this problem

We found out that what we need to know about the waterfall is height and maximum flow rate. We can then state that the flow rate can be related to current, and the height is the "potential"







We then related the waterfall and the generator to how a battery works, and decided that the height, or the potential difference in the waterfall, in terms of electricity is called voltage, and the current is the flow rate of the charge.
Power comes as a result, as it is the amount of energy received by the bulb (or generator)
We can then take all three of these units, and state that P=VI, where P is power in watts, V is voltage in joules/coulomb, and current in coulombs/second

Developing A Model for Current Flow

We were then asked to understand which models of the ones that were provided for us could best describe current. 
We predicted (and were correct) that model D came to be, based on the understanding that current has to be conserved or else the system wouldn't function.









Activity: Measuring Current
We then had to use an ammeter, a device used to detect current, in order to see whether or not current can be positive or negative

Using the obtained ammeter, we set up a simple circuit the way it was directed, and found out that the current flows positively. We then tested again, by flipping the leads, and found the indicator needle going negatively. (It is to note that the number on the ammeter was the same, just different signs)
Due to this model, we can then state that we have effectively proven our model of current flow to be indeed correct



Drift Velocity and Current
The following next few picture is understanding the concept of drift velocity in a current. Back in the waterfall example, we learned that the flow rate is indeed the current and the P=VI; in this example, we are learning the expression of current in a wire using area, velocity, density, and charge and a question based on finding drift velocity.

Derivation of Drift Velocity in a current

An example finding drift velocity

Ohm's Law
Next we went over the idea of Ohm's Law and the understanding of resistance. Using the set up that the video is going, we started to set the power supply to 3 volts, recording the voltages and currents, and then kept continuing till we reached about 12 volts

Our graph result

We eventually find out that the graph of voltage vs current creates a straight line, showing that there is indeed a direct relationship involving the two. Additionally, when the voltage was doubled, the resistance and the power both doubled, showing again a direct relationship between voltage and both resistance and power









Resitivity:
We then disconnected the circuit we had, and connected two wires with clip leads to the meter, in order to test for resistance of two metals, copper and nickel-silver

Our setup

Data Results

We then see that the relationship between resistance and length are actually directly proportional to each other