Building an Electric Motor

Today in physics class we built a simple electric motor with groups of two. To build the motor, we used:

1. a piece of wood
2. four 4-inch nails
3. two strips of aluminum from a pop can
4. 2 smaller nails
5. a couple pieces of Lego
6. two thumbtacks
7. a kebab skewer
8. a long piece of wire
9. a cork
10. two magnets
11. some tape

The motor took me and my partner most of the period to construct. There were some minor hitches when we were unable to push the kebab skewer through the cork, but we fixed the problem by first hammering a nail through the cork to make it easier to insert the skewer.

Our motor worked based on the motor principle, which is based on the fact that when two magnetic fields interact with each other, a force is produced. In this case, the magnets produce one magnetic field, and the current running through the wires coiled around the cork produces the other magnetic field. In order for the motor to spin continuously, the current must be reversed after every half-turn. This will allow the cork to spin in one direction continuously. Our motor's spin was a bit wobbly and unstable, but it still managed to make quite a few revolutions before the power was turned off. This activity was very fun and allowed us to not only learn about the motor principle, but to apply it in a real life situation.

If we did this activity again, I would fix the motor so that spins more smoothly. I think the reason why our motor was so twitchy was because our aluminum strips were too thick, thereby slowing our motor down. If I did this activity again in the future, I would make the aluminum strips thinner.

Here is a video of our motor spinning:



Here are some pictures of our motor:

Our motor during the early stages of its construction.

Just need to add the aluminum strips...

The finished product.

Right-Hand Rules

Here are some pictures explaining the two right hand rules that I've learned so far:

The first right-hand rule (RHR#1) for conventional current flow.

The second right-hand rule (RHR#2) for conventional current flow.

Magnetism and Electromagnetism Notes (Text p. 582-589)

• The magnetic force is a force that acts at a distance. A magnetic field is the distribution of a magnetic force in the region of a magnet.
• There are 2 different magnetic characteristics, north and south, responsible for magnetic forces. Similar poles repel one another, dissimilar poles attract one another.
• To map a magnetic field, we use a test compass or spread iron filings near a magnet.
• Ferromagnetic metals are metals such as iron, nickel, cobalt, or mixtures of these three that attract magnets. All magnets are made up of these metals.
• Domain Theory of Magnets - All large magnets are made up of many smaller and rotatable magnets, called dipoles, which can interact with other dipoles close by. If dipoles line up, then a small magnetic domain is produced.
• Oersted's Principle - Charge moving through a conductor produces a circular magnetic field around the conductor.
• Right-hand rules used to map the magnetic field and predict the direction of the electromagnetic force created by the current running through conductor.
• Right-hand rule #1 (RHR#1) for conventional current flow (for conductors) - Grasp the conductor with the thumb of the right hand pointing in the direction of the conventional, or positive (+), current flow. The curved fingers point in the direction of the magnetic field around the conductor.
• In order to make the conductor magnet stronger and straighten our its field, the conductor is coiled into a solenoid. The magnetic field around a solenoid is like that of a bar magnet. When wire is coiled, individual field lines fall on top of each other, strengthening the overall field. Linear cylinder shape also straightens out the field.
• Right-hand rule #2 (RHR#2) for conventional current flow (for coils) - Grasp the coiled conductor with the right hand such that curved fingers point in the direction of conventional, or positive (+), current flow. The thumb points in the direction of the magnetic field within the coil. Outside the coil, the thumb represents the north (N) end of the electromagnet produced by the coil.
• Electromagnet - a coil of wire around a soft iron core, which uses electric current to produce a magnetic field.
• Strength of magnetic field represented by B.
• Factors that determine strength of electromagnet: current in the coil, number of turns in coil, type of material in the coil's centre, size of coil.
• Some of the uses of electromagnetism: lifting, relay, electric bell.
  

Resistance Notes (Text pg. 553-563)

• The amount of current flow in a circuit depends on two things: the potential difference of the power supply, and the nature of the pathway through the loads that are using the electric potential energy.
• Electrical resistance is the measure of the opposition to current flow.
• The voltage/current (V/I) ratio is constant, and therefore must be the resistance of a load because it remained unchanged through the course of the experiment.
• As a result the equation for resistance is: R=V/I, where R is resistance in Ω (ohm), V is the potential difference in volts (V), and I is the resulting current in amperes (A).
• Ohm's Law states that the V/I ratio was constant for a particular resistor.
• Many factors that affect resistance: length, cross-sectional area, type of material, temperature. (pg. 557)
• Kirchhoff's current law: The total amount of current into a junction point of a circuit equals the total current that flows out of that same junction.
• Kirchhoff's voltage law: The total of all electrical potential decreases in any complete circuit loop is equal to any potential increases in that circuit loop.
• Resistances in Series - the general equation for more than 3 resistors: R[total] = R[1] + R[2] + R[3]... + R[N], where N is the total number of series resistors in the circuit. If the resistors are all the same: R[T] = NR
• Resistances in Parallel - the general equation for more than 3 resistors: 1/R[T] = 1/R[1] + 1/R[2] + 1/R[3]... + 1/R[N], where N is the total number of parallel resistors in the circuit. If the resistors are the same: R[T] = R/N

Electricity Prelab Chart

Name, Symbol, Unit, Definition

Voltage,  V,  v (volt),  The electric potential energy for each coulomb of charge in a circuit.

Current,  I,  A (ampere),  The rate at which charge moves past a point in a conductor.

Resistance,  R,  Ω (ohm),  A measure of the opposition to current flow.

Power,  P,  W (watt),  The rate at which electrical energy is passed on to various circuit loads.

Energy Ball Activity Questions

1) Can you make the ball work? What do you think makes the ball flash and hum?
Yes, I can make the ball work by touching both metal contacts. The ball flashes and hums because my body completes the circuit.

2) Why do you have to touch both metal contacts to make the ball work?
You must touch both metal contacts in order to complete the circuit.

3) Will the ball light up if you connect the contacts with any material?
It will light up if you connect the contacts to anything that is conductive, e.g. anything metal. However it will not work if you connect it to an insulator, e.g. rubber.

4) Which materials will make the energy ball work? Test your hypothesis.
Anything that is a conductor will make the ball work, for example anything metal.

5) This ball doesn't work on certain individuals. What could cause this to happen?
I think it could be because of a deficiency in electrolytes, or severe dehydration, or even dry hands acting as insulators.

6) Can you make the energy ball work with all 5-6 individuals in your group? Will it work with the entire class?
Yes the energy ball works with everyone in the group and with the entire class. It's just that now the conductor is a bit longer.

7) What kind of circuit can you form with one energy ball?
A simple circuit with a battery, load, and a conductor going between the two.

8) Given 2 balls: Can you create a circuit where both balls light up? 1 of 3.
Yes you can create a series circuit with two balls.

9) What do you think will happen if one person lets go of the other person's hand? Why? 2 of 3.
Both of the balls will stop working because the circuit has been broken.

10) Does it matter who lets go? Try it.
No it doesn't matter who lets go because the circuit still gets broken regardless of who lets go.

11) Can you create a circuit where only one ball lights (both must be included in the circuit)? 1 of 2.
Yes, we can create a parallel circuit where the balls run parallel to each other. This type of circuit allows one ball to be switched off while the other is still working.

12) What is the minimum number of people required to complete this? 2 of 2.
It only takes one person to make a compound circuit with two balls, but the person would have to hold the balls in weird way with both of their hands.

Series Circuits vs Parallel Circuits

Here's the difference between series circuits and parallel circuits:

Series Circuits
As you can see in the diagram above, a series circuit is a circuit in which the loads are connected one after another in a single path. As a result, there is only one path for the current to flow when traveling through the circuit.

Parallel Circuits
However, in parallel circuits the loads are connected parallel to each other, side by side. As a result,  there are multiple paths that the current may take. As you can see in the diagram, when the current reaches the junction between the two light bulbs, it splits because there are two paths that the current may take. Half of the current flows through one light bulb, the other half flows through the other light bulb.

Newspaper Structure Challenge

The physics of tall structures 

• There are many forces acting upon tall structures: gravity, wind, etc.
• Many factors influence the stability of tall structures....

What makes a tall structure stable?

• The materials. The tall structure will be more stable if the materials it is made out of are strong.
• The shape. The structure will tend to be more stable if the base is wider than the top of the structure. The stability can also be improved by incorporating strong shapes like triangles into the design of the structure.
• The weight distribution. The structure will be more stable if the bottom of the structure is heavier than the top. If the top is too heavy, the structure could tip over.
• The structure's center of gravity. The structure's center of gravity should be as low as possible, right above center of its base in order to achieve maximum stability.

What is the center of gravity?

• It is the "imaginary point in a body of matter where, for convenience in certain calculations, the total weight of the body may be thought to be concentrated." (Source: http://www.britannica.com/EBchecked/topic/242556/centre-of-gravity)
• Could also be thought of as the "balancing point" of the structure.

Our group's finished newspaper structure.

Electric Currents (Text P. 544-552)

Notes

• In an electric circuit, an energy source provides electrons with energy. Electrons are transported via a conductor to where their energy is transferred. Then they are transported back to the energy source to be re-energized.
• Current is the flow of charge: the total amount of charge moving past a point in a conductor divided by the time taken.
• The formula for current is I=Q/t, where I is current in amperes (A), Q is the charge in coulombs (C), and t is time in seconds.
• 1 ampere = 1 coulomb of charge moving through a point every second.
• Current actually flows from - to +, but in conventional current (model of positive charge flow) current flows from + to -.
• Ammeter is a device that measures current.
• DC or direct current is type of current that flows in a single direction from the power supply to the load.
• Electric Potential Difference (Voltage) is the electrical potential energy for each coulomb of charge.
• Formula for voltage is: V=E/Q, where E is the energy required to increase the electric potential of a charge, Q.
• The formula for the energy transferred by charge flow is E=VIt, where E is energy in joules, V is the potential difference in volts, I is the current in amperes, and t is time in seconds.
• A voltmeter is used to measure electric potential difference (voltage).  

Pictures and Videos

Some of the various symbols used in electric circuit diagrams.

A diagram demonstrating a conventional current.

Some other useful websites:
http://en.wikipedia.org/wiki/Electric_current
http://www.physicsclassroom.com/class/circuits/u9l2c.cfm