EMF is Greater Than Terminal Voltage: Understanding the Relationship Between the Two

Last Updated on 12 months by Francis

In electrical systems, the term EMF (electromotive force) refers to the voltage that is generated by a source such as a battery or generator. While this voltage is often used as a reference point for measuring the energy in a circuit, it’s important to note that in certain situations, the actual voltage across the terminals of a device may be lower than the EMF value. This occurs when there is resistance within the circuit that causes a voltage drop, resulting in the EMF being greater than the terminal voltage. Understanding this concept is crucial in determining the efficiency and performance of electrical systems.

What is EMF?

EMF stands for electromagnetic force, which is the force that causes electric charges to move through a conductor. EMF is measured in volts and is usually represented by the symbol “E.” EMF can be generated by a variety of sources, including batteries, generators, and power supplies.

Understanding Terminal Voltage

Terminal voltage, on the other hand, is the voltage measured across the terminals of a device or circuit. It is the voltage that is available to be used by the device or circuit, and it is usually represented by the symbol “V.” Terminal voltage is affected by factors such as the resistance of the circuit and the amount of current flowing through it.

The Relationship Between EMF and Terminal Voltage

While EMF and terminal voltage are both measured in volts, they are not always the same. In fact, in many cases, the EMF is greater than the terminal voltage.

This is because the terminal voltage is affected by the resistance of the circuit. As current flows through the circuit, it encounters resistance, which causes the voltage to drop. The amount of voltage drop is determined by Ohm’s law, which states that the voltage drop is equal to the current multiplied by the resistance.

Because of this, the terminal voltage is always less than or equal to the EMF. The larger the resistance of the circuit, the greater the voltage drop, and the smaller the terminal voltage will be.

Examples of EMF and Terminal Voltage

To better understand the relationship between EMF and terminal voltage, let’s look at some examples.

Example 1: A Battery

A battery is a common source of EMF. Let’s say we have a battery with an EMF of 12 volts and an internal resistance of 1 ohm. If we connect a circuit with a resistance of 5 ohms to the battery, we can use Ohm’s law to calculate the terminal voltage:

V = E – IR
V = 12 – (5 x 1)
V = 7 volts

In this case, the terminal voltage is less than the EMF because of the resistance of the circuit.

Example 2: A Generator

A generator is another source of EMF. Let’s say we have a generator with an EMF of 120 volts and an internal resistance of 2 ohms. If we connect a circuit with a resistance of 10 ohms to the generator, we can use Ohm’s law to calculate the terminal voltage:

V = 120 – (10 x 2)
V = 100 volts

Again, the terminal voltage is less than the EMF because of the resistance of the circuit.

Misconceptions About EMF and Terminal Voltage

There are several misconceptions about EMF and terminal voltage that are worth addressing.

Misconception 1: EMF and Terminal Voltage are the Same Thing

As we’ve seen, EMF and terminal voltage are not the same thing. EMF is the force that causes electric charges to move through a conductor, while terminal voltage is the voltage that is available to be used by a device or circuit.

Misconception 2: EMF is Always Greater Than Terminal Voltage

While it is true that EMF is often greater than terminal voltage, it is not always the case. If the resistance of the circuit is very small, the terminal voltage may be very close to the EMF.

Misconception 3: Terminal Voltage is the Only Voltage That Matters

While terminal voltage is the voltage that is available to be used by a device or circuit, it is not the only voltage that matters. There may be other voltages present in the circuit, such as voltage drops across resistors or other components.

FAQs – emf is greater than terminal voltage

What does it mean when the emf is greater than the terminal voltage?

When the emf (electromotive force) of a circuit is greater than the terminal voltage, it means that there is some form of resistance in the circuit that is causing a drop in voltage. In other words, the voltage that is being measured at the terminals is lower than the voltage that is being produced by the source (the emf). This can occur due to factors such as the resistance of the wires or the presence of other components in the circuit.

How does this affect the performance of the circuit?

When the emf is greater than the terminal voltage, it can affect the performance of the circuit in a few different ways. Firstly, it can result in a decrease in the current flowing through the circuit, as the higher voltage may not be able to overcome the resistance in the circuit. Secondly, it can cause the components of the circuit to heat up, as the excess energy from the emf is dissipated as heat. Finally, it can cause the circuit to be less efficient, as some of the energy produced by the emf is wasted in overcoming the resistance in the circuit.

Can anything be done to fix this issue?

If the emf is greater than the terminal voltage, there are a few things that can be done to try and fix the issue. Firstly, you can try reducing the resistance in the circuit by using thicker wires or removing any unnecessary components. Secondly, you can try using a voltage regulator or other component to regulate the voltage to the desired level. Finally, you can try using a different source with a lower emf, or adjusting the settings of the existing source to produce a lower emf.