Current, Voltage, resistivity

Lab day 12: 4/9/15: Current, Voltage, Resistivity

Purpose: We look at the different relationships between current, voltage, and resistivity using light bulbs, batteries, and multimeters that allow us to find physical and qualitative meanings to each. The idea of lighting a bulb and connectivity will be analyzed.

Lighting a Light Bulb

We started off class by lighting a light bulb using a battery and a wire. This was done by closing the circuit connecting a wire from the positive terminal to the negative terminal. We were able to look at the basic usage of light bulbs, wires, and batteries. A light bulb consists of a filament that is attached to the end of a bulb which is then attached to the other side of the battery.

We went on to analyze different rearrangements of light bulbs which allows it to light up. When the light bulb filament is not directly on the bulb of the battery, the light bulb will not light up. The light bulb will also not light up when it is not in a closed circuit. This is due to the fact that the electric flow doesn't pass through the filament which is what makes the bulb lit. Therefore the way it lights up is when the bottom end of the battery is connected to the top bulb which has a filament connected to the top end of the battery creating a closed circuit. 

Making it Brighter

We found that when two batteries are put together, the light bulb becomes twice as bright. The light bulb is seen to shine brighter due to more work being done which supplies energy to the bulbs.  

Electroscope

When we supplied a positive charge to the electroscope, we observed that nothing happened. In fact the reason is because in a battery, we can see that a current is being supplied which causes electrons to flow which means work is being done on the bulb to make it lit. 

In fact an important point to be made is that a wire is needed to go back from the bulb to the battery because it allows electrons to flow in and out of the battery resulting in an equilibrium charge in which work is being done to supply the energy.

We can find  the power of this setup using P=IV and we see that a 1.5 volt battery will supply a power of 0.18 J/s .

Old Ammeter Experiment

In this experiment we are able to measure the current that flows into the battery and the current that flows out of the battery using an ammeter. We predicted that it would be the same current in and out as what goes in should be the same going out through the wires. 

The current did end up being the same as the current going out of the wire which proves that the work being done to light the bulb does not affect the current running through the wires even if energy is being used. Therefore we can restate that current does not change with the energy.

The drift velocity was calculated where it is the velocity of the flow current of electrons. The drift velocity depends on the electron charge, area, the number density, and the current.  It is found that current flows through the wire where there is a cross sectional area of the wire which can be used with the current and constant to find the drift velocity. The value we calculated has a magnitude that is small where electrons move very slow.

When we look at current and voltage relationship, we predict that it is proportional and increases linearly. The charge is also constant and proportional in a similar fashion.  The experimental results show that this is true and that there is a dependence on resistance which is the type of material used. Including resistance we get Ohm's law V=IR which explains the relationship between voltage, current, and resistance.

In this part we compare two different wires of different lengths. We found that the 200 cm longer coil has more resistance due to more material. The 160 cm long resistor is shorter which will decrease the resistance. As we measure different lengths of wires we find that the resistance is proportional to the length. As we increase the length, the resistance increases.

Conclusion: We analyzed the relationship between current, voltage, and resistivity by looking at each one separately. We also find that using batteries, wires, and light bulbs we can analyze its relationship through the work-energy supplied to light a light bulb. The current however is not affected by this and remains constant through the wire. The proportionality of current and voltage was found to be related to resistors found using Ohm's law which is not always the best way to calculate resistance. Therefore the equation based on physical properties is a better way to find the resistance of a resistor.