RT= R1 + R2
Ohm’s law is the mathematical relationship between the voltage, current and resistance in an electric circuit. This law states:
Voltage (V) = amps (I) x Ohms (R)
V=IR
The relationship between heat and resistance is demonstrated by the fixed resistor and filament light bulb experiments. When a filament light bulb is used more heat is created than when a fixed resistor was used. Therefore the filament light bulb graph has a curve, while the fixed resistor graph produces a straight line. In these graphs resistance is the gradient or voltage (v)/ current (I).
In a series circuit all the components are connected in a line between the positive and negative terminals. The voltmeter is the only exception as it is always connected in parallel. If one part of the circuit is removed or disconnected the circuit is broken and nothing in the circuit will function until the circuit is complete again.
Prediction:
I predict that as the length of the wire increases the resistance of the wire will also increase. There will be more particles to collide with the mobile electrons so therefore there will be a slowing down of the movement of electrons. When resistors are connected in series the resistance of each resistor adds up to the total resistance. I predict that the length should rise proportionally with the resistance.
How To Make A Fair Test:
I will keep the other factors that effect resistance that I mentioned above the same to ensure I have a fair test. I will be using the same wire for the experiment and the experiment will be conducted at room temperature.
Resistor:
I will put a variable resistor into the circuit to get more accurate voltages. Voltages on lab packs aren’t exact so the resistor will also help prevent damage to the multimeter. I am going to keep the current in the experiment below 150mA using a variable resistor. A reading in milliamps would also give much more accurate results.
Safety:
As electricity is being used care must be taken to positive terminals, negative terminals or bare wires must not be touched when the power supply is on. The resistance wire may heat up as electricity is passed through it so this piece of wire must not be touched will the power supply is on.
Apparatus:
- Power pack
Connecting wires
Variable resistor
Crocodile clips
Metal wire
Voltmeter
Amp meter
Meter stick
Diagram:
Method:
- Set up the apparatus as shown
- Measure the required length of wire
- Place crocodile clips onto either side of the wire
- Turn on the power supply
- Set power pack to lowest setting
- Take readings from ammeter and voltmeter and record in a table
- Repeat steps 2 – 6 for the other lengths of wire
- Repeat each experiment 3 times and record results
-
When all results are collected find the resistance by dividing V/I
- After finding the resistance for the 3 sets of results find the average resistance and record in a table.
- Plot a graph with length in metres on the x-axis and average resistance on the y-axis.
Results Plan:
I plan to record my results in a table as shown below:
From the results recorded I will draw a graph with l/m on the x-axis and average resistance on the y-axis.
Table of Results:
Graph:
Evaluation:
I can see from the results of the experiment that as the length of the wire is increased the resistance increases. The graph that I produced is a straight line graph, so the resistance increases proportionally to the length of wire. The graph is in proportion because each time the length of the wire was increased it was like putting another resistor into the circuit. The circuit is a series circuit and in a series circuit the resistance adds up to give a total resistance. As the length increased there were more particles for the electrons to collide with and therefore it is harder for the electrons to pass through the wire.
Patterns:
The average resistance for a piece of wire, 0.5 m in length is 1.87. I can see that if I double this number I get 3.74, which is very similar to the average resistance for a piece of wire, 1m in length.
Reliability of Evidence:
Digital voltmeters and amp meters were used throughout the experiment. This digital equipment gave a much more accurate set of results. The straight line graph I produced was not an exact straight line, this was due to some of the digits on the amp meters and voltmeters fluctuating so I was forced to estimate the values. Within the circuit the connecting wires offered some resistance, which added to the resistance of the wire. This may have caused slight changes in the results. Crocodile clips are 4/5 mm in size. Therefore the lengths of resistance wire may be inaccurate.
Prediction:
As I predicted the length of wire increases proportionally to the resistance. There are more particles present in a longer piece of wire and therefore a slowing down of the electrons. This causes a higher resistance as the length is increased.
