Lab 6: Electrical Motors Members in the group : 1. Nattanit Trakullapphan (Nam) 1101 2. Thaksaporn Sirichanyaphong (May) 1101 3. Paradee Unchaleevilawan (Pop) 1101 4. Punyawee Lertworawut (Earl) 1101 5. Inchanok Prasittiphontavee (Inn) 1101 Objectives: To understand how an electric motor works. To calculate the magnetic field. Materials: Copper wire Two needles One foam support Universal stand and clamps Vernier Magnetic Field sensor LabQuest Laptop with Logger Pro Small permanent magnet Sand paper Procedure 1. Making the solenoid: a. Roll the copper wire around the permanent magnet (use the magnet as a template to assemble the solenoid). Make five turns. Take the permanent magnet out. b. Use the extra wire on both extremes to make two or three turns to hold the turns of the solenoid together (see figure below).
c. Cut the wires at the extremes so they are no more than 2 cm in length on both sides. 2. Assembling: a. Stick the needles on the foam support separated by no more than 4 cm. b. Rub each end of the solenoid with the sandpaper to make sure they have good electrical contact. c. Stick each end of the solenoid to the holes of each needle so the solenoid is suspended between the two needles. 3. Measuring the magnetic field and current a. Connect the power supply to the LabQuest interface and the interface to your computer. Open the power amplifier control window and set it up to DC. b. Connect the power amplifier, the current probe and the needles as shown on the diagram on the board. c. Turn on the power amplifier. Zero the current probe when the voltage in the power amplifier is set to 0 V. d. Apply a voltage of no more than 3 V. Check if you have current in the circuit (should be no more than 0.6 A). e. Record the current in the table. f. Calculate the magnetic field in the solenoid with the formula given in the background section. Record this value in the table. The Length of the coil can be estimated with: L = # of turns X thickness of the wire (assume the thickness of the wire is 200 µm) g. Connect the magnetic field sensor to your LabQuest. CAUTION: Do not bring the field sensor to a close distance with the permanent magnet. Make sure they are at least separated by 30 cm. h. Hold the sensor using the clamp and the universal stand. Zero the sensor when it is away from the coil. i. Bring the sensor close (a few millimeters) to the solenoid and record in the table the value of the magnetic field. Make sure that the circular area of the sensor is parallel to the circular area of the solenoid
4. Running the motor a. Disconnect the current probe and connect the power amplifier to the two needles. b. Apply a voltage between 4 8 V. c. Bring the permanent magnet close to the solenoid and observe what happens. d. Find an optimum position for the permanent magnet in order to make the solenoid rotate for the longest time. If you find a position in which the solenoid turns without stopping, it is even better. e. Record a video of the motor running Result: Data Table Voltage (V) Current (A) Mag. Field (Calculated) Mag. Field (Measured) 1.5 V 0.057 A 3.58 10 8 tesla 0.066 tesla Analysis : 1. Is the magnetic field measured in agreement with the calculated magnetic field? => No, the calculated magnetic is 3.58 10 8 tesla while the magnetic field measured is around 0.066 tesla. 2. Explain step by step why the solenoid keeps turning. Use diagrams. In your explanation, include the forces and concepts that are involved. => According to the experiment, we made the solenoid by rolling the copper wire around the permanent magnet to make the loop shape of wire and use the extra wire on both extremes to make two or three turns to hold the turns of the solenoid together, as shown in the picture below.
Then we sticked each end of the solenoid to the holes of each needle, which one side was connected to the positive charge and the other was connected to the negative charge. This indicated the direction of current flow as shown in the picture below from the positive to negative charge so the electricity was sent through the wire to make the electromagnetic field. Also, according to the right hand rule, the thumb will indicate the direction of the current while other four fingers will indicate the direction of the magnetic field so in our solenoid the direction of the magnetic field will point like this: However, this was the electromagnetic field that was created due to the moving of electron of the current but it didn t make our solenoid to turn. The magnetic field from the permanent magnet instead made the solenoid to keep turning.
According to the picture above, the permanent magnet created the magnetic field whose direction was pointing into the loop of the solenoid while the direction of current was still going through the wire from the positive charge to the negative charge. Therefore, base on the right rule, the force would point to the upper side making the solenoid to keep turning in that direction. 3. Investigate and explain another type of electrical motor. Use diagrams and mention the forces and concepts involved. => Linear motors are electric induction motors that produce motion in a straight line. The stator is unwrapped and laid out flat and the rotor moves past it in a straight line as seen in the picture below. [3]
If the pairs of magnets are pulsed on, from right to left, so the region of magnetic field moves from right to left. [2] A permanent or electromagnet will tend to follow the field. Linear motors often use superconducting magnets, which are cooled to low temperatures to reduce power consumption. One example of linear motor application is a high speed maglev train. 4. The magnetic field sensor works due to the Hall Effect? Investigate and explain what the Hall Effect is. => The Hall Effect is the phenomenon of the presence of the transverse voltage that is produced between the two sides of a conductor by balancing the magnetic influence during the buildup of charge at the sides of the conductor. [1] A side of the conductor is where the moving charge carriers are pushed to when the magnetic field, where an electric current flows through a conductor, exerts a transverse force on. Thus, we can say the Hall Effect can be used to measured the magnetic field with a Hall sensor. A Hall sensor is based on the physical principle of the Hall Effect. It detects the voltage generated transversely to the current flow direction in an electric conductor if a magnetic field is applied perpendicularly to the conductor. [1]
Conclusion: Based on what we ve learned from the classes, we were now making our own electrical motor to observe how it did work. By making our solenoid from the rolled copper wire and sending the electric current through the wire, we then used the permanent magnet to create the magnetic field and observed that the solenoid kept turning due to the force occurred based on the right hand rule. The force on the wire carrying current made the solenoid to turn in its direction, and as we kept holding the permanent magnet, the solenoid would keep turning. However, this was one example of the electrical motors that were used in the electric appliances in our daily life. In addition, another type of electrical motors is a linear motor which can be run by both direct current and alternative current. This motor type is in a straight path rather than a rotating motor, which is applied to a high speed train, such as Shinkansen. The train is moved by the induction of the magnetic field fixed in the rail. The error we had in this experiment was the problem with the power amplifier. At first, the LabQuest interface couldn t measure the electric current in the circuit because the current was still zero although we increased the current to 3V. This problem was due to the inefficient wire connecting between the power amplifier and the LabQuest interface so it caused the connection lost and we couldn t measure the electric current in the circuit. However, when tried to plug in the wire again many times, it then worked so we could continue doing our experiment. Even though, the problem due to the equipment in the lab wasn t something we could predict, but we could minimize these problems in the future by checking the equipment before and after doing the lab and told the instructor that there was a problem with the equipment so he could know and fix the equipment before other labs next time. Other experiment our group can do further based on the results from this experiment is to find out what factors that cause the value of magnetic field measured isn t in agreement with the calculated magnetic field.
References [1] Hyperphysic. (n.d.). Hall Effects [Online]. Available: http://hyperphysics.phy astr.gsu.edu/hbase/magnetic/hall.html [Wednesday. 1 April 2015 21.29] [2] UNSW. (n.d.). Electric motors and generators [Online]. Availbale: http://www.animations.physics.unsw.edu.au/jw/electricmotors.html#inductionmotors [Wednesday. 1 April 2015 20.47] [3] Woodford, C. (2014). Linear motors [Online]. Available: http://www.explainthatstuff.com/linearmotor.html [Wednesday. 1 April 2015 20.35]