Ohms law is used to calculate the voltage, current and resistance. Ohms lawThis 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. Preliminary Vin (v) Vin measured (v) R1 (? ) R2 (? ) Vout 12 0. 32 1. 2 10k 0. 28 12 0. 35 4. 7 10k 0. 24 12 0. 37 7. 5 10k 0. 21 12 0. 47 8.

2 10k 0. 2 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 Power pack This device supplies the circuit with electric power. It would be used at 12 volts. It is much more accurate to use than batteries or cells. And the end results would be in numbers that are easy to read and handle. Digital Multi meter An ammeter measures the current in a circuit, a voltmeter measures the voltage. A multimeter combines these functions into a single device. It will be used at 20 volts Wires (four plus the two connected to the multi meter)

The wires would be used to connect the resistors components and the power pack together. The plastic casing means that when the wires do get hot (due to high resistance) that I wouldn’t burn my hands if I touched them. Crocodile clips (four) The crocodile clips are simple mechanical devices used for creating a temporary electrical connection. They are a much more efficient and effective way of joining the circuit together rather than twisting the end wires together. Resistor 1 Resistor 1 resistance will range from 10k 12k 15k 18k 20k 22k 43k 56k 75k 100k Resistor 2

During the actual method resistor 2 were always be kept at 47k ohms 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. Results table Vin (v) Vin measured Risk assessment Hazards 1. 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. 2. Sharp flying metal particles can damage the eyes. 3. Long hair is likely to get caught in the wires of the circuit. 4. 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.

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.