Motor

Simple Motor

Today, in the physics class, our group learned how to build a simple motor with materials such as cork, wires, wood, thumbtack nails, and aluminum pieces. The motor are basically divided to different components - the commutator, split-ring, conductor, and power supply. The commutator involves two pins that are metal that are fixed in the cork so they can attach to the brushes located at the both sides of the commutator while spinning (aluminum pieces), and the electricity will pass through the metal conductor to the wires wrapped around the cork. While electricity passing through the wires been wrapped around the cork, magnetic field is created which makes a up force at one side and a down force at the other side due to the direction of current flow, so overall the commutator could spin a complete circle. In the process of building a simple motor, there are few details that needs to be further noticed otherwise, the motor will not work at the first time. The brushes made of aluminum pieces from cans are needed to be rubbed by sandpaper until the silver-shiny surface appear, otherwise electricity will not passes through them. The wires are also required to be rubbed at the end and the beginning part which then will wrap around the pin. For building the commutator, wires should be wrapped neatly, and parallel to each other.

Magnetic Force

Right Hand Rule #1

Right Hand Rule #2

• Magnetic Field is the distribution of a magnetic force in the region of a magnet There are two different magnetic characteristics, labelled North and South.
• Similar magnetic poles, north and north or south and south, repel one another. Dissimilar poles, north and south, attract one another with a force at a distance.
• Metals such as iron, nickel, and cobalt, or mixtures of there metals, are called the ferromagnetic metals, which means they could be attracted by magnets.
• Magnets are made of ferromagnetic metals
• Domain Theory states that 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.
• Domains that line up could make the metal be magnetized.
• Oersted's Principle: Charge moving through a conductor produces a circular magnetic field around the conductor.
• Right-hand rules are three rule about magnets fields that involves your right hand. The abbreviation for them are RHR#1, RHR#2, and RHR#3.
• Right-hand rule#1: For conventional current flow, grasp the conductor with the thumb of the right hand pointing in the direction of conventional, or positive (+) current flow. The curved fingers point in the direction of the magnetic field around the conductor. There is a Left-hand rule#1, which is just opposite to RHR#1
• Scientists curve the conductor to strengthen the magnetic field.
• RHR#2: For conventional current flow, 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 tin the direction of the magnetic field within the coil. Outside the coil, the thumb represents the north end of the electromagnet produced by the coil.
• Left-hand rule#2: Opposite to RHR#2, the left-hand thumb grasp the coiled conductor, pointing the direction of the electron (-) current flow through the conductor.
• Electromagnet is a coil of wire around a soft iron core, which uses electric current to produce a magnetic field.
• Important formulas in the chapter are B2 = B1(I2/I1), and B2 = B1(n2/n1) - both of them are for calculating the strength of an electromagnet (B).

Resistance - Ohm's Law and Kirchhoff's Laws

• The amount of energy transferred to a load depends on two things: 1. the potential difference of the power supply and 2. the resistance of the pathway through the loads that are using the lectir potential energy.
• Resistance directly affect the amount of current passes through the load. Low resistance makes current to pass through the load much more easily.
• The measure of the opposition to flow is called electrical resistane.
• R = V/I is the formula for calculating resistance. R is the resistance in volts/ampere and unit is Ω. V is the potential difference in volts and I is the current in amperes.
• The Ohm's law states that the V/I ratio is constant for a particular resistor.
• The amount of current flowing through a resistor varies directly as the amount of poetential difference applied across the resistor. The higher the potential difference, the more the current flows through the resistor.
• The resistance on a conductor depends on many properties such as Length, corss-sectional area, the material it is made of, and its temperture.
• The formula for calculating the resistance of  conductors in difference length  R1/R2 = L1/L2.  
• Cross-sectional area that affects the resistance, the larger the area or thicker the conductor, the less resistant it has to current flow. It is represented as R1/R2 = A2/A1
• Some materials are better conductors than other materials. The measure of the resistance of a substance is called resistivity. It has units Ω m. It is represented as R1/R2 = p1/p2
• Temperature also works as one factor that changes resistance of a substance. Unsually the higher the temperature the higher the resistance, however, not for all substances.

Prelab: Using Voltmeter and Ammepter

Name	Symbol	Unit	Definition
Voltage	V	V	Potential difference for each coulomb of charge in a circuit.
Current	A	A	The flow of charge
Resistance	R	Ω	The opposition to current flow
Power	P	W	The rate at which work is performed or energy is converted

Qustion 1 - 12

1. Touch two metal contacts to make the ball flash.
2. To create a complete electric circuit
3. The ball will not flash. It needs a conductor, and it will flash only when the two materials that works as the conductor connects forming a complete circuit. 
4. The materials we tested are metal, and human body. Both of them could work as conductor.
5. When the body is not attached to the metal contacts which means covered by something such as clothing.
6. We can make the energy ball work with all people as long as a complete circuit is established.
7. A series circuit
8. We could make both ball light up in either a series circuit or a parallel circuit.
9. If two balls are in one circuit when on person disconnects with the other, the balls will not light up. If there are two circuits when on person disconnects in a circuit, the other circuit still operates.
10. In a series circuit, no.
12. 4 people.

Series Circuit and Parallel Circruit

Series Circuit

Nice Website that explains Everything!

Series circuit is a electric circuit in which the loads are connected one after another. In a series circuit there is only one path from the source through all of the loads and back to the source. This means that all of the current in the circuit must flow through all of the loads. Opening or breaking the circuit at any point will cause the loads, for example, light bulbs in the circuit all start operating or stop operating. This is the main disadvantage of a series circuit. If any one of the light bulbs or loads burns out or is removed, the entire circuit stops operating.

Parallel circuit is a circuit in which there are at least two independent paths in the circuit to get back to the source.The loads in a parallel circuit connect side by side. In the circuit, the current will flow through the closed paths and not through the open paths. Consider an example, in the example a switch and a 60 watt light bulb is acquired. If the switch is closed, the light operates. When a second 60 watt bulb is added to the circuit in parallel with the first bulb, it is connected so that there is a path to flow through to the first bulb or a path to flow through to the second bulb. In such circuit both bulbs glow at their intended brightness, since each of them receives the full circuit voltage.
Every load connected in a separate path receives the full circuit voltage. If a third 60-watt bulb is added to the circuit, it also glows at its intended brightness since it also receives its full volts from the source.

The concern in parallel circuits is that it is very easy to overload a circuit by adding loads in which more current is flowing in the circuit than it could safely handle. 

An obvious advantage of parallel circuits is that the burnout or removal of one bulb does not affect the other bulbs in parallel circuits. They continue to operate because there is still a independent closed path from the source to each of the other loads.

Challenge

Oriental Pearl Tower

Yesterday we did a fun activity which is to use newspapers to build a tower as high as possible in a group. We were allowed to use whatever method except for taping the newspapers directly on the table in which a fixed base would be created. At the beginning, we first thought about the shape of base and came up with two ideas: triangular or rectangular. Soon we decided to use a rectangular base instead of using a triangular one. The reason is that the newspapers were limited in the amount. So a lighter and thinner base could save more paper for later use. The method we used to build up the tower is that we make each level smaller and lighter than the previous one, so that the top does not gravitate to other sides. However, as the tower reaches a certain height, the top automatically leans to one side. So we decided to put small pieces of paper at the opposite side of the leaning side in order to balance the weight. The typical problem that we faced is that the upper part falls from the middle. So what we did is to avoid that from happening. The final product is not ideal although it stands alright. At the end what we learned is that for tall buildings, a triangular base or the main building that gains support from triangular structure would be much more stable than other bases in different shape. A sample  could clearly explain the idea would be the Oriental Pearl Tower in Shanghai, China. One more thing that needs to be mentioned is that the centre of gravity which is the average location of the weight of an object. The key factor for building up a building is to establish the centre of gravity at the middle.

Current Electricity and Electric Circuits

Rate of Charge Flow

Electric Potential Difference

Basic Symbols

• Electrons repel on another makes electric current.
• In the formula of calculating the rate of charge flow, I represents the current in amperes which is the base unit for current, Q represents the charge in coulombs - a electric unit represented by C, and t represents the time in seconds.
• The time must be converted to seconds in any of the calculation.
• The electric current-measuring device is called ammeter.
• DC, an abbreviation for direct current, in which the current flows in a single direction from the power supply through conductor to a load.
• AC is the abbreviation for alternating current, in which the flowing direction of the current periodically reverses with the help of electric and magnetic forces.
• Charge does not flow on its own, but a complete circuit allows the excess charge to be able to "see" a region of charge deficit.
• Power supply sets up an electric field. Electric charge in the electric field has a certain amount of electrical potential energy.
• The power supply increases the electrical potential energy of each coulomb of charge from a low to high value. The electrical potential energy of charge decreases as it flows though load.
• In the formula of electric potential difference, V stands for the electric potential difference, E stands for the energy required to increase the electric potential of a charge (Q).
• One volt (V) is the electric potential difference between two points if one Joule of work is required to move on coulomb of charge between the points.
• Formula E = VIt is used to calculate the amount of energy in joule; V represents the potential difference in volts, I is the current in amperes, and t is the time in seconds.
• Potential difference between any two points can be measured by using a voltmeter and the voltmeter must be placed parallel with the load.