Docstoc

Factors affecting the resistance of a wire

Document Sample
Factors affecting the resistance of a wire Powered By Docstoc
					Physics piece of coursework. Aim is to complete one more piece of coursework before Xmas. Any improvements will be made before February 2005. You need to complete at least 2 FULL investigations (P O A E) Factors affecting the resistance of a wire Aim 1. To set up an electric circuit to measure the resistance of a wire 2. Take appropriate measurements to calculate the resistance of a wire 3. Know what factors affect the resistance of a wire. Starter What does resistance mean? What is current? Why do we use a voltmeter and ammeter in an electrical circuit?

Factors affecting the resistance of a wire Aim 1.To set up an electric circuit to measure the resistance of a wire 2.Take appropriate measurements to calculate the resistance of a wire 3.Know what factors affect the resistance of a wire. Starter What is everything made up of? What are atoms made of? What is the charge of each particle within an atom?

Resistance means to oppose the flow of electricity in a circuit. A current is a flow of electrons round a circuit. We measure the flow of using a ammeter. The unit of current is amperes (A). An ammeter is connected in series in an electrical circuit. The ‘push’ of current through a circuit is the voltage. We measure the voltage in a circuit using a voltmeter. The unit of voltage is volts (V). The voltmeter is connected in parallel in an electrical circuit. Activity 1: Draw a circuit with an ammeter and voltmeter connected correctly Activity 2: List 4 ways a wire can be different. Activity 3: How can what you said in activity 2 affect the flow of electrons in a wire? Resistance can be calculated using Ohms Law: Resistance = Voltage Current

Activity 4: what measurements will you need to record to calculate the resistance of a wire? Draw a table of the results you will record.

Resistance = Voltage Current
Length of wire (cm) 10 10 20 20 30 30 40 40 50 50 60 60 70 70 80 80 90 90 100 100 Voltage (V) Current (A) Resistance (Ώ) Average Resistance (Ώ)

Calculating resistance of a wire. Objectives 1. To calculate resistance using: Resistance = Voltage Current 2. Plot a graph of length and resistance. 3. Draw a labelled diagram of the equipment used and stat what measurements you will take.

Firstly Look at your results; use a calculator to work out the resistance. To calculate the average resistance add the 2 resistances for the same length together and divide by 2. Secondly Plot a graph of length of wire against average resistance. Draw a line of best fit and circle any points that are not in line with the rest. Thirdly Write a simple method. Draw a basic electricity symbol circuit. Say what you will change, keep the same and what measurements you will take.

PLANNING Draw a labeled diagram of the circuit you used. Use standard symbols not pictures. Now write a list of the equipment you used and how much of each you used Write down what measurements you will take? (What results will you write down?) Explain what you are going to change and what you will keep the same. Did you change the length, type of wire, thickness or temperature of the wire? SCIENTIFIC THEORY Explain what resistance means. How do we calculate resistance? Describe how electricity flows round a circuit. Explain what is current. How are the atoms in the wire made up of particles? What part of an atom carries the electricity? How does increasing the length of wire increase the resistance? How does changing the thickness affect resistance? If the wire gets hot will this affect the flow of electricity? How?

Correct version
Current is the flow of electrons round a circuit. Electrons are found moving around quickly on the outer part of atoms. They have a negative charge. Atoms are made up of protons, electrons and neutrons. In the nucleus of the atom we find the proton and the neutron. Protons have a positive charge and neutrons are neutral. Opposites are attracted together. A positive will be attracted to a negative and vice versa. The electron that moves along the wire carrying the current will be attracted to the positive nucleus of the atom. This creates a resistance. Resistance means to stop something. In this case it means to stop the flow of electricity around a circuit. Resistance is calculated using Ohms Law: Resistance = Voltage Current The longer a piece of wire is the more atoms there are in that wire. This means there are more electrons to carry the current. The negative electron will be attracted to the positive nucleus as it travels along the wire. The less wire the less attraction within the wire so the less resistance there will be.

False
Current is the flow of protons round a circuit. Electrons are found moving around quickly on the outer part of atoms. They have a neutral charge. Atoms are made up of protons, electrons and neutrons. In the nucleus of the atom we find the proton and the electrons. Protons have a positive charge and electrons are neutral. Opposites are attracted together. A positive will be attracted to a negative and vice versa. The proton that moves along the wire carrying the current will be attracted to the positive nucleus of the atom. This creates a resistance. Resistance means to stop something. In this case it means to stop the flow of electricity around a circuit. Resistance is calculated using Ohms Law: Resistance = current voltage The longer a piece of wire is the more electricity in that wire. This means there is more electricity to carry the current. The neutral electron will be attracted to the positive nucleus as it travels along the wire. The less wire the less attraction within the wire so the less resistance there will be.

Incorrect order
Protons have a positive charge and neutrons are neutral. Opposites are attracted together. A positive will be attracted to a negative and vice versa. The electron that moves along the wire carrying the current will be attracted to the positive nucleus of the atom. This creates a resistance. Current is the flow of electrons round a circuit. Electrons are found moving around quickly on the outer part of atoms. They have a negative charge. Resistance means to stop something. In this case it means to stop the flow of electricity around a circuit. The longer a piece of wire is the more atoms there are in that wire. Atoms are made up of protons, electrons and neutrons. In the nucleus of the atom we find the proton and the neutron. The negative electron will be attracted to the positive nucleus as it travels along the wire. Resistance is calculated using Ohms Law: Resistance = Voltage Current This means there are more electrons to carry the current. The less wire the less attraction within the wire so the less resistance there will be.

Analysis

Plot a graph of your results. Resistance v.s. length Draw a line of best fit (the best straight line) Give the graph a title. Look at the graph and your results and answer the following questions:  Is there an overall pattern to the results? Say what the pattern is.  Do the results seem to be in a line? If they are say so and what this means. If not say so and what this means. E.g. the resistance is proportional to the length of a wire  Explain why your results were as they were. (Hint – check your reason for the prediction) if it was correct say it again. If not give an alternative explanation.  If you have time repeat your experiment with a different material. This allows you to check your theory is true generally for metals. Evaluation  Pick out any results that do not seem to fit and try to explain why they happened e.g. circuit left on and heated up increasing the resistance, there was a kink in the wire etc  Can you suggest any improvements to the apparatus used or technique e.g. using an even lower voltage and current to limit heating effect? Or use a data logger for more continuous and instantaneous readings.  Did any errors influence your results? (Hint – high resistance = more heat generated will alter the results.) Therefore a longer length is more affected by heating then shorter ones.


				
DOCUMENT INFO