Equipotential 4/9/2014

Today we had our little fiesta... the question asks we to arrange two batteries and two light bulbs and make them 1) as bright as possible and 2) as dim as possible.  After the whole chaos of struggling to find the right setup, it turns out that the correct arrangement for brightest setup is to back to back the battery to double the voltage while keeping the light bulbs parallel.  As for dimmest setup, it is to keep the batteries parallel while  back to back the bulbs to double the resistance.

 Circuit with the series-batteries configuration (brighter = greater potential)

Circuit with the parallel-batteries configuration (dimmer = lasts longer)

After the fiesta, prof started the lab and used a much sophisticated immersion heater made out of resistive coils to heat a cup of water.  Similar to the beginning of the semester, we used a power meter to find power-supplied:

Experiment configuration hooked up to Logger Pro probe to plot data

By knowing the voltage and the mass of water, we first find the resistance of the boiling apparatus.  Given the mass of the water, the dimensions of the coil (cm long), and the applied voltage (4.5V), time (10 minutes) we can find the final temperature. Since our calculated resistance of the coil and the current flowing through  is different from other groups.  We then used then difference of resistivity different current to come up with an uncertainty for the current.  After determining the power, the energy put into the water, and the change in temperature with uncertainty, the actual change in temperature is as follows:

 (Click above images to see lab calculations on our whiteboards)

Next, we used the same process and changed the initial voltage from 4.5 volts to 9 volts. As calculated, it turns out that doubling the voltage did not double the change in temperature.  We then turned the spotlight to Eddie and put all the stress on him.  Eddie then finally says it would not have doubled because doubling the voltage also doubles the current, which increases the power by a factor of four.

Calculation of 4.5 V

Next, calculation of 9.0 V

Graph of the temperature change from logger pro. The blue data set was the 9.0 V experiment and the red data set was the initial 4.5 V experiment. According to logger pro, for the 4.5 V, T_initial was about 23°C and T_final at about 25°C for DeltaT of 2°C. The 9.0 V experiment initialed at 24.6°C and ended at 32.1°C for a DeltaT of 7.5°C.  it actually almost quadrupled. The reason for this can be shown mathematically.

When R remains the same, the new current is substituted into the power equation and the voltage increases 4x

Then we began lecture of an introduction of potential differences over a region.

Prof Mason demonstrates the perspective from a charge particle as it interacts with a positive potential (left) or a negative potential (right)

We wrapped up the day with a burnt hot dog party.  By putting a 110 volt (that is non lethal) through two different brand of hot dogs, we wanted to see other than the burnt stinky smell, if we were able to cook them with such electric potential.

 Ready to cook some dogs!!

LEDs instantly burned out due to massive overwhelming potential

EEEWWWWWWW~ STINKY DOGS SENSATION OF 1974!

We then stick little LED emitters into the hot dogs to see if they light up differently depending on the opening of their legs.  It turns out that the wider their legs are open, the brighter they glow before completely burning out.  This is due to the potential difference of power between the legs- greater difference = brighter.