When electricity is introduced however the negatively charged electrons will instantly begin to move through the wire in the same direction (towards the positively charged end) this is an electric current, a current is the flow of charge in a wire or the movement of the negatively charged electrons through the wire.
The electrons move like this because of the voltage (energy/ power) which “pushes” the current around the circuit. The energy is transferred from the power pack to the electrons that will equally share and give out the energy to each component in the circuit. By the time the electron has reached the end of the circuit it will have lost all the energy it will have in gained at the start (energy will be lost through components and resistance.)
Resistance is the opposition that the electrons will experience while flowing through the wire. An electron travelling through the wires encounters resistance. An electron does not travel in a direct route; instead it adopts a zigzag path due to the countless collisions with the atoms in the conducting material.
When electrons move against the resistance, "friction" is generated. The friction produced by electrons flowing against the resistance will cause the wire to heat. (The hotter the wire, the higher the resistance.) Resistance depends on the material, cross section and length. Resistance limits the amount of current flowing through the circuit for a given voltage of the power supply.
For a circuit to work there must be no breaks, if there is a break then everything stops. An electric charge must also go all the way round the circuit. When a wire heats up they will act differently and a blockage will be made. This is a sign of Resistance. I have chosen to keep the voltage at 12 volts as this is the highest number of volts possible on the power pack. Using a higher voltage In, means that I will get higher results for Vout. I will also be able to record them in numbers that are easy to handle and work with, and a more significant range.
Even though I have chosen my voltage to stay at stay 12 volts due to the power packs being not completely accurate, the voltage In will, change because I will be purposefully changing the resistance of the circuit. Everything in a circuit is not mutually exclusive; when one factor is changed every other factor will also change, as they are all interlinked and dependent on each other. As I know that the Voltage In will change, I will make sure that every time I test the resistance of the circuit I will also check the voltage of the circuit and record the result for that down too.
Ohms law is used to calculate the voltage, current and resistance.
Ohms law: Voltage = Current * Resistance
(Volts)/(V) = (Amps)/ (I) * (Ohms Ω)/ (R) V = I R
- Voltage Input (Vin) =12 volts
Voltage In (Vin) measured = 0.32
R1 = 1.2 Ω
R2 = 10k Ω
Vin = current * resistance (Vin = I * (R1+R2))
Current = voltage / resistance (I = V/R)
Vout= I *R2
Vout = Vin * R2
(R1 +R2)
Vout = 0.32 (v) * 10000 (R)
(1.2+10000) (R)
Vout = 3200/ 10001.2
Vout = 0.31996
Vout = 0.32 (2.s.f)
- Voltage In (Vin) measured = 0.2
R1 = 8.2 Ω
R2 = 10k Ω
Vout = I *R2
Vout = Vin * R2
(R1 +R2)
Vout = 0.2 (v) * 10000 (R)
(8.2+10000) (R)
Vout = 2000/ 10008.2
Vout = 0.199836
Vout = 0.2 (2.s.f)
This shows that when the resistance is increased by 7 (ohms) the voltage out decreases by 0.12 volts. I.e. at 1.2 ohms the Vout calculated to 0.32 (volts) And at 8.2 (ohms) the Vout calculated to 0.2 (volts) This shows a difference of 0.12. (volts) So this means that by every 1 (ohm) the voltage goes up by 0.017 (0.02 2.s.f)
Preliminary
In my Preliminary work I used the time to decide what equipment and method would be best to use. I decided to change the following factor (Resistor 1.) I could have changed my Vin or even R2 and I would have received just as satisfactory data for those variables, but I decided to change R1 as it seemed the most promising variable at the time.
I set up my experiment in a science lab as it is the most appropriate venue for an experiment. If an accident had occurred then I would have be able to take the necessary actions needed quickly with the necessary equipment. I set the experiment out in the middle of the bench, following the usual lab safety rules of, bags coats of out of harms reach, spillages cleaned at once, goggles worn used to stop small pieces of metal from accidently piercing someone’s eyes ect.
First I made sure that resistor 1 and resistor 2 were attacked to the three wires, using the four crocodile clips that were also attached to the ends of the wires. Then making sure that the multi meter was set to 20 (volts) I turned the power pack on to 12 volts. I then measured the voltage by using the two wires from the multi meter and connected them to the power pack to measure the voltage in. (I did this to be accurate as the voltage in changes, look above for further information.) Then I measured the resistance of resistor 2 as this would give me the voltage out. Once I had done this, I would immediately turn the power pack off, for health and safety reasons, but also so that the resistance/ ohms of the resistor doesn’t change either. I will then repeat this method for each of the following units for resistor 1.
In my preliminary I decided that the apparatus used were good enough to use in the actual experiment. But the method used wasn’t very reliable as I didn’t do any repeats. This was unreliable for two reasons because one there was no way for me to distinguish whether my data was false or not (outliers) and two I could not create an average. An average result of your data gives you a much more accurate answer to the “actual” value/ answer. The more repeats you do, the closer your average is to the actual answer. Repeats increase the validity of your average. I have chosen to repeat each separate part of the method three times.
Apparatus list
Method
Again I set up the experiment in a science lab as it is the most appropriate venue for an experiment. I set the experiment out in the middle of the bench, following the usual lab safety rules. I then set up the apparatus following the same method I used in the preliminary work.
I made sure that resistor 1 (10k ohms) and resistor 2 (47k ohms) were attacked to the three wires, using the four crocodile clips that were attached to the ends of the wires. Then making sure that the multi meter was set to 20 (volts) I turned the power pack on to 12 volts. Once the power pack is turned on I must measure the Vin by connecting the two wires from the multimeter to the power pack. (If numbers come in negatives then the wires must be switched round.) I did this again for accuracy reasons, as the voltage is bound to change as I am purposefully changing the resistance of the circuit. The power pack itself isn’t a hundred percent accurate either. Then I would measure the resistance of resistor 2 as this would give me the voltage out. I did this by connecting the wires from the multimeter to either ends of resistor 2.
Once I had done this, I would immediately turn the power pack off, for health and safety reasons, but also so that the resistance/ ohms of the resistor doesn’t change either. Then I would keep resistor 2 the same but would change resistor 1 to 12k this time. I would repeat the method above until I have done all of the different values needed for resistor 1, to the highest value chosen 100k ohms. Then I would for repeat this whole process for every resistor 1 value, another two times, to give me an average reading for Vout. The importance of averages has been explained above.
Again if the control variables are not controlled then can affect the experiment and give me false data. They must be controlled to make sure that I am measuring the affects of the input variable, Resistor 1.
The result 0.29 is an outlier and so I decided to repeat that result and I got 0.24 and the average of 0.23+0.24+0.24= (ans)/ 3= 0.236 = 0.24
Risk assessment
Hazards
- Burns are likely, if there is a high resistance, the friction caused by the atom and electron collisions will cause the wire to heat up.
- Sharp flying metal particles can damage the eyes.
- Long hair is likely to get caught in the wires of the circuit.
- If too much current flowing through the wires, the circuit is likely to blow up.
Precautions
The usual lab rules plus the following factors must be followed.
Safety goggles must be worn to prevent the damaging of the eyes. The experiment must be done standing up. Gloves should be considered if you are working with a high resistance; the circuit must be handled with care. Hair must be tied and clipped back. Make sure you are working in a clear work space. If for any reason spillages/ breakages occur they must be cleared at once. And avoiding crowding of other people as this can cause accidents. Switch off the circuit (once you have finished recording the measurements) at once.
A fixed amount of positively charged ions (purple) surrounded by negatively charged electrons (blue) in an electrically conducting wire.
The more resistance (i.e. the more atoms) there is in a wire, the harder it is for the electrons (the current) to get around the circuit. And so these collisions between the atoms and electons cause friction, which creates the heating effect on the wire. The resistance effectively slows down the current.
Draw two wires one with lots of atoms and little resistance and one with a few atoms and low resistance.
R= V / I
R1 + R2 = Vin / I
Current = Vin / R1 + R2
Vout = I * R2
The part of the equation in red is another way of calculating the current without actually needing to know the actual value for it.
This is how the apparatus was set out.
In my preliminary work we set up the experiment like this. I used a Digital multi meter (it was used because it can measure in both volts and amps.) I used five wires including the two attached to the multi meter, and 4 crocodile clips. Two resistors, resistor 1 and resistor 2. I kept the ohms of resistor 2 the same (at 10k ohms) and resistor 1 was changed each time. (1.2, 4.7, 7.5 and 8.2.) For the power source I used a power pack whose highest voltage was 12 volts.
