1. TEMPERATURE: affects resistance as when the temperature of a metal increases the resistance of the metal increases and the current decreases. The reason for this is because as the temperature increases the atoms of the metal tend to vibrate more vigoursly each time as of the increase in energy. This in turn makes it more difficult for the electrons to move across the wire as they collide with the atoms of the metal on the way to the positive end of the wire, therefore increasing the amount of collisions meaning there is/would be more resistance.
However, keeping the temperature constant throughout the experiment could prove fairly difficult as the temperature could easily increase or decrease, unless you have the correct apparatus to keep the temperature constant or complete the experiment on the same day at room temperature. It is essential to use a low voltage as it will mean a low current which will not heat up the wires. If a high voltage was used then the energy would be in the form of heat which will affect the resistances and therefore make the experiment unfair.
Out of the two types of wires provided (Nichrome and Constantan), nichrome would be unreliable as it is affected by temperature, which therefore will affect the resistance, where as constantan wouldn’t and instead would provide you with better results. 2. LENGTH: of wire affects resistance as when you increase the length of the wire the resistance also increases. The reason for this is because there would be an increase in atoms as well as the electrons having to make their way further up the wire to the positive end, which in return creates a greater chance of the electrons colliding with the atoms and therefore meaning more resistance.
3. THICKNESS: of a wire affects resistance as the greater the thickness, the more electrons that can travel through the wire at the same time, which therefore means a decrease in resistance. An example of this could be that say a school hall (wire) was full of hundreds of people (electrons) and they all left the hall through one door, they would have to form a line and leave (greater resistance), however if two or more doors were open they could leave at the same time (lower resistance). A Micrometer can be used to measure the width/ thickness of the wire.
4. MATERIALS: affect resistance as different materials have different resistances. An increase in the number of atoms in the material mean there will be an increase in the number of electrons, resulting in a lower resistance as of the gain in electrons. However if the particles in the material are cramped together it would result in the electrons having more collisions with the atoms and therefore more resistance. These factors/variables must be kept constant (except the length of the wire) throughout the experiment in order to produce reliable results.
INDEPENDENT VARIABLE: will be the length of the wire as this will be changing throughout the experiment. I have decided to start with a wire of length two meters long, and as I continue the experiment I will decrease the length by 10cm intervals each time, which should about give me enough results to plot an accurate graph and comment on it. DEPENDENT VARIABLE: will be the resistance as this really depends upon the length, material of wire, temperature and also thickness of the wire. Resistance involves collisions of the current-carrying charged particles with fixed particles that make up the structure of the conductors.
A resistor is a material that makes it hard for electrons to go through a circuit. Without resistance, the amount from even one volt would be infinite. Resistance occurs when electrons travelling along the wire collide with the atoms of the wire. APPARATUS / EQUIPMENT: APPARATUS AMOUNT REASON Voltmeter 1 To measure the voltage of the circuit in volts Ammeter 2 To measure the current of the circuit in amperes. There are two types, one reading from 0 – 1A and the other form O – 2A. Insulated Circuit Wires Approx. 6 To produce / make the circuit required for the experiment.
Crocodile Clips 2 To attach to the Constantan Wire when taking the reading at 10cm intervals and also provides safe contacts between the components and the wire. Meter Ruler(s) 1 or 2 To measure accurately the length of Constantan Wire required and to be able to take measurement at 10cm intervals. Constantan Wire 2 meter length It is the wire for which the resistance is going to be investigated for in the circuit and conduct electricity. Power Supply 1 To allow a current to flow to the circuit. Micrometer 1 To accurately measure the thickness of the wire being used.
METHOD: 1. Collect all the apparatus or equipment required in order for this experiment to go ahead. 2. Use the Micrometer to measure the thickness of the wire. 3. Using the meter ruler measure out 2m of Constantan wire (Black, 28swg). 4. Cello tape the wire across the 2m ruler. Taught the wire so it is a straight a possible but do not over do it as it possibly could make the wire become thinner. 5. Connect insulated circuit wires and crocodile clips to the power pack/supply. 6. Connect or attach circuit wires to the voltmeter and Ammeter. 7.
Place one crocodile clip on the 0cms and place the other at the point of measurement on the constantan wire. In this case every 10cm intervals. 8. Record your findings to a table of results. I will be using two different ammeters, one ranging from 0 – 1A, used for smaller readings of resistance and the other 0 – 2A, because it is better for larger readings. Overall the ammeter ranging from 0 – 1A is more accurate as it read in intervals of 0. 05A while the other reads in intervals of 0. 2A. RESULTS TABLE: Power (P) Length (cm) Current (I) Voltage (V)
Resistance (R) SAFETY: 1. Handle the power supply carefully. 2. Be careful when touching the wire as it may be/get hot during the experiment. 3. Start on the lowest current, so the wire will not melt or burn instantly. 4. Make sure the main to the power supply is switched off each time when measuring at the 10cm intervals. 5. All wire to cool between experiments as temperature effects resistance. 6. Ensure the power supply is switched off before making any alterations to the circuit.
PRELIMINARY WORK: Before carrying out the actual experiment, a preliminary test was carried out to find out how the length of a wire affects the resistance. This is so a prediction could be made and so the outcomes could be seen which may enable us to produce more accurate and reliable results on the actual experiment which follows. METHOD FOR PRELIMINARY TEST: 1. Collect all the apparatus or equipment required in order for this experiment to go ahead. 2. Using the meter ruler measure out 1m of Constantan wire (28swg). 3. Cello tape the wire across the 1m ruler.
Taught the wire so it is a straight a possible but do not over do it as it possibly could make the wire become thinner. 4. Connect insulated circuit wires and crocodile clips to the power pack/supply. 5. Connect or attach circuit wires to the voltmeter and Ammeter. 6. Place one crocodile clip on the 0cms and place the other at the point of measurement on the constantan wire. In this case every 10cm intervals. 7. Record your findings to a table of results. RESULTS: Power (P) Length (cm) Current (I) Voltage (V) Resistance (R).
7 My preliminary results have shown that ‘as the length of a wire increases the resistance also increases. I have used the ammeter ranging from 0 – 1A as it is more accurate (reads in interval of 0. 05A) but have lowered the voltage on the power pack/supply so all results range between 0 – 1A. Linked to this, I have also found that if the voltage is too high on the power pack/supply, the reading on the voltmeter will go off the scale and will be unreadable thus the reason why the voltage should be/was lowered.
However, an ammeter ranging from 0 – 2A could be used instead; this though is not as accurate as the 0 – 1A ammeter as its scale ranges in intervals of 0. 2A. Lowering the voltage on the power pack does/may not affect the resistance when worked out using the formula Resistance (R) = Voltage (V) / Current (I), as shown on the preliminary results produced. PREDICTION: I predict that as the length of a wire increases the resistance also increases in proportional to the length.
This is because there would be an increase in atoms, as well as electrons having to make their way further up the wire to the positive end which in return creates a greater chance of electrons colliding with the atoms and therefore meaning more resistance. To this point doubling the length would mean an increase in the number of atoms which would result in twice as many collisions, which would in turn slow down the flow of electrons and increase the resistance. Halving the length would mean the opposite, half the atoms, half the collisions and therefore a decrease in resistance.