| 103 | | |
| 104 | | == Electromagnets == |
| 105 | | |
| 106 | | == DC Motors == |
| 107 | | |
| 108 | | * Exercise: use a multimeter to measure the current flowing through a DC motor |
| 109 | | * Materials needed: multimeter with leads, two jumper wires with alligator clips, SLA or 9v battery, DC motor |
| 110 | | * Activity: |
| 111 | | * Set up materials as in the exercise above |
| 112 | | * Unplug the bulb from the circuit |
| 113 | | * Connect the positive wire (alligator jumper wire connected to the positive battery terminal) to one of the motor wires or terminals |
| 114 | | * Connect the multimeter red wire to the other motor wire or terminal |
| 115 | | * The motor spins! |
| 116 | | * observe the amount of current flowing in Amperes on the multimeter display |
| 117 | | * What happened: Just as water turning a hydroelectric turbine in a dam converts some of the mechanical turning energy into electrical energy (flowing electrons), the DC motor converts some of the energy from electrons flowing through it into mechanical rotational energy. The DC motor contains coils of wire that allow electricity to flow from one terminal to the other (and cause the motor to spin in the process). The work the motor can do is proportional to the power (voltage * current) of the electrons flowing through the circuit. |
| 118 | | |
| 119 | | * Exercise: make the motor change directions by reversing the direction of current flow |
| 120 | | * Materials needed: multimeter with leads, two jumper wires with alligator clips, SLA or 9v battery, DC motor |
| 121 | | * Activity: |
| 122 | | * Set up materials as in the exercise above |
| 123 | | * Disconnect the positive wire from the motor terminal it is connected to, noting which terminal that is (we'll call it P) |
| 124 | | * Disconnect the multimeter red wire from the other motor terminal (we'll call it N) |
| 125 | | * Reverse the connections so the positive wire connects to terminal N and the multimeter red wire connects to terminal P |
| 126 | | * The motor spins the other direction! |
| 127 | | * What happened: The direction the DC motor spins is determined by the direction of the flow of electrons through it. |
| 166 | | * Bonus Exercise: measure the resistance of other things (e.g. your fingers). Try it with your fingers moist and dry and observe the difference. |
| | 139 | * Exercise: measure the resistance of other things (e.g. your fingers). Try it with your fingers moist and dry and observe the difference. |
| | 140 | |
| | 141 | * Bonus Exercise: make your own light bulb. |
| | 142 | * Materials needed: pencil leads, alligator jumper wires, battery, tape, cardboard tube (e.g. TP or paper towel) |
| | 143 | * Activity: |
| | 144 | * see the [https://www.youtube.com/watch?v=wucmSj7Z-dA Crazy Russian Hacker]. Note: if you wanted the filament to last longer, fill the glass with an inert gas like Argon and seal it. |
| | 145 | * What happened: the resistance of the pencil lead to the electricity flowing through it converts electrical energy to heat and light. |
| | 146 | |
| | 147 | == Electromagnets == |
| | 148 | [[Image(http://cdn.hitfix.com/photos/4366059/Magneto-floats-on.jpg,20%,right,nolink)]] |
| | 149 | When electricity moves through a conductor, it [https://www.khanacademy.org/test-prep/mcat/physical-processes/magnetism-mcat/a/using-the-right-hand-rule generates a magnetic field] around the conductor. If you shape the conductor into a coil (like a spring), the field is concentrated and becomes stronger. The more current, the stronger the magnetic field. Industrial electromagnets can lift 25-30,000lbs (think truck); electromagnets hold the door shut at the bank. 2537 has used electromagnets to hold and release heavy mechanisms. |
| | 150 | |
| | 151 | * Exercise: |
| | 152 | * Materials: battery, electromagnet, alligator jumper wires |
| | 153 | * Activity: |
| | 154 | * Connect the electromagnet to the battery terminals |
| | 155 | * Pick stuff up with the magnet |
| | 156 | |
| | 157 | |
| | 158 | == DC Motors == |
| | 159 | |
| | 160 | DC Motors are what make robots move. A DC motor converts electrical DC current to magnetic force using two or more electromagnets. The electromagnets are arranged so that their magnetic fields alternately attract and repel to turn the motor shaft, converting magnetic energy to rotational force. How a motor does this is explained in a short video [https://www.youtube.com/watch?v=LAtPHANEfQo here] that you should watch. |
| | 161 | |
| | 162 | * Exercise: make a motor spin |
| | 163 | * Materials needed: two jumper wires with alligator clips, SLA or 9v battery, small DC motor |
| | 164 | * Activity: |
| | 165 | * Use an alligator jumper wire to connect one terminal of the battery to one of the motor terminals or wires |
| | 166 | * Use another alligator jumper wire to connect the other battery terminal to the other motor terminal or wire |
| | 167 | * Watch the motor spin! |
| | 168 | * What happened: Just as water turning a hydroelectric turbine in a dam converts some of the mechanical turning energy into electrical energy (flowing electrons), the DC motor converts some of the energy from electrons flowing through it into mechanical rotational energy. The DC motor contains coils of wire that allow electricity to flow from one terminal to the other (and cause the motor to spin in the process). The work the motor can do is proportional to the power (voltage * current) of the electrons flowing through the circuit. |
| | 169 | |
| | 170 | * Exercise: make the motor change directions by reversing the direction of current flow |
| | 171 | * Materials needed: two jumper wires with alligator clips, SLA or 9v battery, small DC motor |
| | 172 | * Activity: |
| | 173 | * Set up materials as in the exercise above, note the direction the motor spins (clockwise or counterclockwise) |
| | 174 | * Disconnect the original wire from the positive battery terminal and connect it to the negative battery terminal |
| | 175 | * Disconnect the original wire from the negative battery terminal and connect it to the positive battery terminal |
| | 176 | * The motor spins...observe the direction! |
| | 177 | * What happened: The direction the DC motor spins is determined by the direction of the flow of electrons through it. |
| | 178 | |
| | 179 | * Exercise: use a multimeter to measure the current flowing through a DC motor |
| | 180 | * Materials needed: multimeter with leads, two jumper wires with alligator clips, SLA or 9v battery, small DC motor |
| | 181 | * Activity: |
| | 182 | * Connect the positive wire (alligator jumper wire connected to the positive battery terminal) to one of the motor wires or terminals |
| | 183 | * Connect the multimeter red wire to the other motor wire or terminal |
| | 184 | * The motor spins! |
| | 185 | * observe the amount of current flowing in Amperes on the multimeter display (idle current) |
| | 186 | * use your fingers to slow down the motor (but don't stop it) and observe the change in current (load current) |
| | 187 | * What happened: as the load on the DC motor increases, so does the amount of current it draws. Note that if you stall the motor completely, the energy from the battery will continuously be going through one electromagnet which will heat up and eventually fail (often with smoke and sometimes flame involved). When the motor is spinning, the energy (and heat) are divided among all of the electromagnets in the motor, giving each a chance to cool down. On heavy duty motors, the shaft often includes internal fan blades that push air across the hot electromagnet coils to keep them cool. |
| | 188 | |
| | 189 | |
