In 1918, Edith Clarke broke through a male-dominated field to become the first female electrical engineer in America. Clarke specialised in power system analysis and wrote influential books on electricity. Through the story of Edith Clarke, we’ll explore the physics involved in electricity – how it’s generated and how it changed the world.
Edith Clarke was born in 1883, in Maryland USA. After being orphaned at age 12, she was raised by her older sister. She used her inheritance to study mathematics and astronomy at Vassar College, where she graduated in 1908. After college, Clarke taught mathematics and physics at a private school in San Francisco and at Marshall College. She then spent some time studying civil engineering at the University of Wisconsin–Madison, but left to become a “computer” at AT&T in 1912. While at AT&T, she studied electrical engineering at Columbia University by night. In 1918, Clarke enrolled at the Massachusetts Institute of Technology, and the following year she became the first woman to earn an M.S. in electrical engineering from MIT.
Her background in mathematics helped her achieve fame in her field. On February 8, 1926, as the first woman to deliver a paper at the American Institute of Electrical Engineers’ annual meeting, she showed how to calculate the maximum power that a line could carry without instability. Two of her later papers on electricity won awards from the AIEE: the Best Regional Paper Prize in 1932 and the Best National Paper Prize in 1941. In 1947, she joined the faculty of the Electrical Engineering Department at the University of Texas at Austin, making her the first female professor of Electrical Engineering in the country. She taught for ten years and retired in 1957.
Electricity is essential to our everyday lives. Without it we wouldn’t have our phones, computers, kettles, televisions or any modern appliance. Electricity has been known for all of human history, we can see it in the form of lightning in the sky. But it wasn’t until the year 1800 that we could harness electricity and create it in the lab. Since then, technology has been transformed by electricity. Have you ever tried to make your hair stand up by rubbing a balloon on your head? This is an example of static electricity, which we are not going to get into. Instead we’re going to focus on current electricity.
Current electricity works on the principle of the flow of negative charges (electrons) between atoms. The flow of charge is called a current and in physics we use the symbol I. The unit of current is the ampere (A). Electricity can only flow in certain types of materials. Objects that allow current to pass through them are known as conductors (metals), while objects that do not allow current to easily pass through them are called insulators (wood, glass, plastic). If we join a number of conductors to a power source we can form a circuit.
Electric circuits are the basis of how we power electrical appliances. A battery is used to generate the current in the circuit. The current flows from the positive side of the battery to the negative side, making a complete circuit. As you add an objects into the circuit (e.g. a light bulb), the current flows through them and back to the battery. Different materials react differently to current, and this is due to their resistance. Resistance is the ability of a material to resist the flow of electric current and is measured in Ohms (Ω).
There are two different types of electric circuit; series and parallel. In a series circuit, the current flows through each component one after the after. If one component in the circuit fails, current stops flowing. In a parallel circuit, the current does not have to flow through every component, they are all connected independently of the others. This means that if one component fails, the rest of the circuit continues to work. An example of this would be your Christmas lights. Think of the rows of hundreds and hundreds of light bulbs. Have you ever noticed that one of the bulbs has blown, but the rest of them stay lit? This is because the bulbs are connected in a parallel circuit. You can learn a lot from observing different circuits either in series or parallel with different numbers of components.
Have a go making your own electric circuits using the batteries, wires and light-bulbs in this simulation below.
Resistance, Current and Voltage
We’ve seen a few ‘triangle relationships’ in the junior cert physics course so far and they are very useful relationships in physics. We’ve seen ones like Distance = Speed / Time and Density = Mass / Volume and there is another relationship that deals with electricity. The physicist Georg Ohm studied the relationship between current, voltage and resistance and made it in to a handy formula that says resistance is equal to voltage divided by current (Resistance = Voltage / Current). This relationship helps us figure out how much voltage we need to put through an object if we know its resistance and what current we want to achieve (Voltage = Current x Resistance).