The most common misunderstanding among students is the difference between EMF and voltage. As both have the same units so people consider both of them as one term. But actually, both are different. To understand the distinction between EMF and voltage, we must first define the terms EMF and voltage.
What is EMF?
EMF stands for electromotive force. In the absence of an electric current, EMF is the voltage at the source’s terminals. The definition of EMF is given as the amount of work required to separate the charge carriers in the source current such that the force acting on the charges at the source’s terminals is not a direct result of the field. Internal resistance causes the development of emf. Thus, electromotive force is the amount of work done in the energy transformation as well as the amount of electricity that passes through the electrical source or generator. EMF is measured in Volts and denoted by the symbol ε. The EMF is the energy supply from the source to each coulomb of charge. In other words, it is the energy supplied to the unit coulomb charge by an active source such as a battery. The above-mentioned circuit’s electromotive force is represented by the formula
ε = I (R + r)
Here r denotes the circuit’s internal resistance. R is the circuit’s external resistance. ε stands for electromotive force and I presents current.
What is Voltage?
The amount of energy required to move a unit charge from one end to the other is defined as the voltage. Voltage is denoted by the symbol V and the unit of voltage is volts. The voltage is generated primarily between the two poles of the electric circuit, i.e. between the anode and cathode of the battery. The positive terminal of the battery is referred to as the cathode, while the negative terminal is referred to as the anode. The potential at the source’s cathode will be greater than the potential at the anode. The voltage drop occurs when a potential difference or voltage is developed across the passive elements. (Passive elements-electrical elements that do not generate power, such as resistors and capacitors, and are used to dissipate and store charges). The voltage produced is the result of an electric field.
The definition of voltage is given as the amount of energy required to move a unit charge from one location to another. The electric and magnetic fields cause the voltage. Kirchhoff’s law states that the sum of voltage drops in a circuit equals the EMF, which actually tells us the relation between voltage and emf.
What is back emf?
Motors and generators have been found to be very similar. Motors convert electrical energy into mechanical energy, whereas generators convert mechanical energy into electrical energy. Furthermore, motors and generators are built in the same way. When a motor’s coil is turned, magnetic flux changes and an emf is induced. When the motor’s coil rotates, it acts as a generator. This will occur whether the shaft is turned by an external input, such as a belt drive, or by the motor’s own action. That is, an emf is generated when a motor is working and its shaft is turning. According to Lenz’s law, the emf opposes any change, so the input emf that powers the motor will be opposed by the motor’s self-generated emf, which is referred to as the back emf of the motor.
What is the difference between EMF and voltage?
The voltage discovered is very small in comparison to emf, and it is the result of the internal resistance of the source itself, which is causing the voltage drop. EMF is made up of electrically charged particles that form as a result of the separation of electrons from atoms through the use of some type of energy, such as chemical, mechanical, or light energy.
EMF = W / Q
Here W is the amount of work done and Q is charge. Whereas, voltage is defined as the difference between the electrical states of the poles. Electrons move from the negative to the positive half of a closed electrical circuit. The work performed by the electric force in moving the charge from one point of the field to another is referred to as electrical voltage.
Difference between emf and voltage
- The EMF is a measure of the amount of energy supplied to each coulomb of charge, whereas the voltage is the amount of energy required for one coulomb of charge to move from one point to another.
- The EMF is represented by ε, whereas the voltage is represented by the symbol V.
- The EMF is measured between the source’s end points when no current flows through it, whereas the voltage is measured between any two points in a closed circuit.
- The electrochemical cell, dynamo, photodiodes, and so on generate the EMF, whereas the voltage is caused by the electric and magnetic fields.
- Current flows between two points due to a potential difference or voltage difference. The potential difference between two electrodes is maintained by EMF.
- The formula of voltage is simply given by Ohm’s law: V = I R, whereas the formula of emf is different: ε = W / Q or ε = I (R +r).
- Voltage is dependent on the circuit’s resistance while emf doesn’t.
- Voltage is the effect of EMF and EMF is the cause of voltage.
- The value of emf is always greater than voltage.
- The intensity of emf is always constant while the voltage intensity varies by the voltage drop across the external resistance.