Assessment
Aim
The aim of this assessment is to investigate the factors that will affect the resistance of a length of resistance wire.
Factors
- Length of wire
- Thickness of wire
- Temperature-We can’t do this factor because it is very hard to control and measure, also the resistance doesn’t change until the wire gets red hot.
- Type of wire-The school only has two types of wires, Constanton and Nickrome, we haven’t got a good selection of wires to choose from so we can’t do this factor.
Method for Length
To calculate the resistance,
We are using the equation;
A
R=V
A
To start of with, you set up the equipment as shown in the diagram.
- Check that the circuit is in working order by putting a resistor in that you know the resistance of, and use the equation to calculate the resistance.
- The resistance wire is to be cut at 50cm.
- Take the readings off the Volt and Amp metres.
- Record results in an appropriate results table.
- Repeat once more with a fresh piece of wire, so you can take an average.
- Do a minimum of seven different lengths, using the same wire withn the same thickness.
Method for Thickness
A
V
- To start of with, you set up the equipment as shown in the diagram.
- Check that the circuit is in working order by putting a resistor in that you know the resistance of, and use the equation to calculate the resistance.
- The resistance wire is to be cut at 40cm.
- Take the readings off the Volt and Amp metres.
- Record results in an appropriate results table.
- Repeat once more with a fresh piece of wire, so you can take an average.
- Do a minimum of seven different thicknesses, using the same type of wire.
Theory of Electricity
An Atom is composed of positively charged particles and much smaller negatively charged particles called electrons. The protons form the center of the atom, while the electrons whirl in an orbit around the proton center, much likes the moon orbits around the earth. If there were multiple earths very close together, and they each had a moon, they could play a game of catch, passing the moons from one earth’s orbit into the next earth’s orbit. But the laws of our game require that each earth has one moon in orbit around it. If an earth didn’t have a moon in orbit, having just passed it, it would have a positive charge on it, and desires to have a moon. If an earth had an extra moon, having just caught one, it would have a negative charge to it, desiring to repel the extra moon. The passing of moons would continue until all earth’s again had one moon in orbit.
CurrentThe flow of electricity in a wire is like this passing of moons. A wire is made out of a material called a conductor. A conductor is a material that likes to play this game of musical chairs. Wires are covered with materials called insulators, because insulators don’t like to play this game. That keeps passing electrons inside the wire.
When electrons are passed form an atom; they leave a “hole.” Holes are potential receptors from other atoms and give the atom a positive charge that attracts negatively charged electrons form other atoms. This flow of electrons form one atom to the next is what we call “electricity.”
The flow of electricity is more properly called “current flow,” or simply “current.” Current is the workhorse of electrical theory. The flow of electrons is what actually produces the power that we consume from the wall socket. “Voltage” is the pressure on the electrons to move form atom to atom. Voltage sits in the wall socket waiting to move electrons, but is only the “potential” for work. If you don’t plug anything into the wall socket, voltage can’t do anything for you. But when you do plug something in, voltage determines how fast those electrons will come streaming out, and consequently how much current will flow; and how much power can be consumed.
Resistance We are about to put the final piece of the puzzle together – resistance. Resistance “impedes” the flow of electrons. Resistance and impedance are related, but for now we are only concerned with resistance.
Resistance is measured in ohms. A light bulb has resistance. The filament resists the flow of electricity, and glows white hot in doing so. The resistance causes the bulb to only allow a portion of the current available in the wall socket, to flow out. A 100-watt light bulb uses more electricity from the wall than a 60-watt light bulb because the filament in a 100-watt bulb has less resistance to it. This lower resistance allows more current to flow through the bulb, consuming more power, producing more work and making more light. This work, by the way, is called “Wattage.” If you multiply the voltage times the current answer is in watts.
