You’ve likely heard the phrases EMF and terminal voltage thrown around before. However, do you truly know what they mean and the way they vary? Don’t worry, you are not alone. A lot of humans count on them being the same element while in fact, they discuss two wonderful electrical properties. Stay with us, and we will demystify those fundamental electric ideas for you.
Defining EMF and Terminal Voltage
To recognize the difference between electromotive force (EMF) and terminal voltage, we want to go back to the fundamentals of energy.
- EMF
EMF refers back to the voltage generated by using a supply of electrical electricity which includes a battery or generator. It’s the quantity of electrical pressure or “push” that moves electrons via an entire circuit. The EMF depends on the source of energy, not the components in the circuit. It remains constant as long as the source is operating.
- Terminal Voltage
Terminal voltage refers back to the voltage measured throughout the terminals of a source while it’s connected to a circuit. Unlike EMF, the terminal voltage depends on the components linked within the circuit, like resistors, as well as the internal resistance of the supply. As the current flows through the circuit, energy is lost due to this internal resistance, causing the terminal voltage to drop.
In short, EMF is the maximum possible voltage that can be supplied by an energy source, while terminal voltage is the actual voltage available for driving current around the circuit.
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To illustrate the difference, think of EMF as the voltage generated by a battery and terminal voltage as the voltage that actually reaches your device when you connect it. If you use thin, low-quality wires, for example, the terminal voltage will drop due to energy lost as heat. However, the EMF rating of the battery remains the same.
Understanding the difference between these two concepts allows you to properly assess voltage requirements for circuits and determine if a given source can actually power your devices as intended. While a battery may have a high EMF, if its terminal voltage drops too low under load, it won’t be useful!
Real-World Examples Comparing EMF and Terminal Voltage
- A Car Battery
The electricity stored in an automobile battery is measured by its electromotive force or EMF. That is the total quantity of ability energy in the battery. However, the voltage you measure on the battery terminals, the terminal voltage, is lower. That is because some of the EMF is misplaced as heat and light at some stage in the chemical reaction in the battery. The terminal voltage will also drop further when you turn on components like headlights or the radio that draw power from the battery.
- A Power Outlet
The power lines outside your house deliver electricity at a very high voltage to reduce power loss over lengthy distances. This high voltage corresponds to a high EMF. But the voltage is stepped down before entering your home for safety and practicality. The terminal voltage at your wall outlets is 120V in North America. This lower terminal voltage corresponds to a lower EMF that is more suitable for powering electronics and appliances in your home.
- Solar Cells
Solar cells convert mild power into electrical electricity via the photovoltaic effect. The EMF generated by a sun cell depends on the intensity and wavelength of the light hitting it. This EMF represents the total potential electrical energy that could be produced under ideal conditions. However, the terminal voltage at the output of the solar cell is lower due to unavoidable inefficiencies and loss mechanisms. The difference between EMF and terminal voltage is an important concept in engineering more efficient solar cells.
Comparing EMF and terminal voltage helps in understanding where energy is lost or used in a system. While EMF represents the total potential energy, terminal voltage accounts for the realities of imperfect efficiency and illustrates how much of that energy is actually available for useful work. Using real-world examples helps to clarify this key distinction.
EMF Vs Terminal Voltage
EMF
- EMF stands for electromotive force, which is the voltage generated by a source like a battery or generator.
- EMF exists even without any load connected, as it’s the potential generated by the source itself.
- EMF has a fixed value for a given source.
- EMF always has the same direction, from the positive terminal to the negative terminal of the source.
- EMF is measured using a potentiometer, with the source disconnected from any loads.
Terminal Voltage
- Terminal voltage refers to the voltage measured at the terminals of a load related to the supply.
- Terminal voltage seems only when a load like a light bulb or motor is hooked up to the source.
- The terminal voltage depends on the load in the circuit and will vary based on factors like the load resistance.
- The terminal voltage has the same direction as the current through the load.
- Terminal voltage is measured directly across the load using a voltmeter.
In summary, EMF and terminal voltage are related but different concepts. EMF powers the circuit, while terminal voltage powers the load. Understanding the distinction among those two voltages will help in studying and troubleshooting electronic circuits.
