Measuring tiny volumes with precision and accuracy requires a micropipet. In the biology lab, micropipets are used for preparing and loading DNA samples, microscale experiments and the preparation of many types of samples. These applications rely on good technique to reduce error. This guide explains how to choose the proper micropipet for the application and techniques to help ensure that measurements are accurate and precise.
Hans Christian Oersted (1777–1851), a Danish physicist, was performing an experiment in 1820 when he noticed that whenever an electric current from a battery was switched on or off, a nearby compass needle was deflected. Through additional experiments, Oersted was able to demonstrate the link between electricity and magnetism. The following year, English scientist Michael Faraday (1791–1867) created a device that produced “electromagnetic rotation.” This device is known as a homopolar motor since the motor requires no commutator to reverse the current.
A motor converts electrical energy to mechanical energy. The simple motor in this activity changes the electrical energy output by the battery to mechanical energy as the copper wire is set into rotational motion. Any current-carrying wire produces an associated magnetic field. The electrons in the wire are subjected to a magnetic field and experience a force—referred to as the Lorentz force—that is perpendicular to both the magnetic field and the direction of movement. At some point along the length of the wire, the electrical current is not parallel to the magnetic field. The resulting Lorentz force is tangential and induces a torque on the copper wire. This torque causes the copper wire to spin.
When charge moves, we call it electric current, but the word current is usually reserved for things like water flows. Does electric current really work like that? Electrons are quantum particles, so we have to be careful.
What’s Going On?
When a magnet is moved by a coil of wires, you can induce an electric current. This is the principle behind how most of the electricity is produced in the world; it’s just a question of where you get the energy to move the magnets. Every time a magnet passes the coil, a small amount of electricity is created, which makes the LED lights briefly flash on. Continue reading
This is the third part of a series of blogs written to suggest teaching methodology for the topic “Electricity”. Brief descriptions of Parts One and Two have been included below.
Part One: Models: In the picture below, soup cans are used to represent students. Actual students formed in a circle will pass and receive playing cards (electrons). Students pass the cards on command, when the teacher says “PASS”. A potential boost occurs at the battery, a potential drop at the light bulb. Students are assigned roles at a switch, a load, or a battery. At a load, the student can be asked to twirl at each pass to simulate work being done.
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Thanks for sharing Dave!
Ever wonder how lightning works? Scientists are still figuring it out, but what we do know is fascinating. Learn about positive and negative lightning, red sprites, blue jets, and ball lightning in this episode of SciShow! Hosted by: Michael Aranda Continue reading
The traditional incandescent bulbs used for teaching series and parallel circuits are rated for 3 V or 6 V. The problem is that many power supplies can generate higher voltages. As a result, it is common to have many blown bulbs. With several sections teaching this unit, bulbs can quickly become in short supply. Bulb replacements can cost $1.00 each, and often are included in the general department order at the end of each semester.
LED as an alternative: LED lights are rated for low voltages (3 V). However, by adding a small resistor (390 ohms) to one of the legs, the LED can be used at excessive electric potentials. After adding the resistor, the LED was successfully used at 13.88 V, the maximum value for my power supply.
Construction: The resistor and LED wire were twisted together. To be consistent, the resistor wire was attached to the anode (+) leg of the LED. To identify this, the LED was held up to a light. The smallest metal in the LED bulb is the anode (+). Solder paste was added to the two twisted wires. Using a pencil style soldering gun, the smallest drop of solder was added on to the soldering iron tip. The tip touched the paste and they were instantly soldered. Start to finish the whole process took less than a minute.
The advantages: The LED’s now can function at higher voltages, the legs can easily fit into breadboards or can be alligator clipped into circuits, and they are cheap. A kit with 100 LEDS, and 390 ohm resistors costs less than $12.00 from Qkit Electronics, Kingston Ontario.
This was initially presented at OAPT 2018 at Western University, London Ontario.
STAO Safety Chair
This TED talk demonstrates a novel and fun way to investigate series and parallel circuits using plasticine as the conductive medium. The Playful Learning Lab website provides sample activities, videos and recipes for making plasticine.