Difference Between emf and Voltage Important Questions

EMF is the potential difference generated by one or multiple cells or a changing magnetic field in a solar cell. Voltage is the potential difference measured at any two points in the magnetic field. The SI unit and voltage of EMF are the same (volt).

Difference Between Voltage and EMF

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Very Short Answer Questions [1 Mark Questions]

Ques. The terminal potential difference of a cell is greater than its e.m.f when it is being charged. Explain.

Ans. It is known that In charging V>E. where V is potential difference and E is emf of the cell.

Ques. State the relationship between line voltage & phase voltage and line current & phase current of a 3phase delta connected system.

Ans. V_ph = V_L ; I_ph = I_L / \(\sqrt{3}\)

Ques. Define voltage regulation of transformer.

Ans. The voltage regulation of the transformer is the percentage change in the output voltage from no-load to full-load.

Ques. The emf of a cell is always greater than its terminal voltage Why? Give reason.

Ans. The emf of a cell is greater than its terminal voltage because there is some potential drop across the cell due to its small internal resistance.

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Short Answer Questions [2 Marks Questions]

Ques. A battery of electromotive force 12V and internal resistance 2Ω is connected to a resistor. If the current of 0.5A is flowing through the circuit then calculate the resistance of a resistor. If the circuit is closed then what will be the terminal voltage of the cell?

Ans. Using KVL,

ε=Ir+IR

12=0.5(2+R)

R=22 Ω

Terminal voltage is: V=ε−Ir=12−0.5×2=11 V

Ques. An alternating voltage is given by V=230sin314t. Calculate i)frequency, ii)maximum value, iii)average value, iv)RMS value. 

Ans. Frequency F = 1 /T =43.5 Hz

Maximum value Vm =Vrms/2 = 230 /2 =115 V

Average value:35.6V

RMS value = Avg value / form factor =35.6 / 1.11 = 32.07 V

Ques. Assume we have a circuit with a 3.2 V potential differential and a current of 0.6 A. At 0.5 ohms, the battery’s internal resistance. Make use of the EMF formula.

Ans. Given:

• V = 3.2 V
• I = 0.6 A
• r = 0.5 ohms

Using Formula:

E = V +Ir

   = 3.2+ 0.6×0.5

   = 3.5V

So, the EMF of the circuit is 3.5V.

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Long Answer Questions [3 Marks Questions]

Ques. What is EMF?

Ans. EMF or Electromotive Force is the energy supply to the charge by a battery cell. In other words, EMF produces and maintains voltage inside an active cell and supplies energy in joules to each unit of coulomb charge. It is represented by “ε” and the measuring unit is the same as voltage i.e. Volt.

EMF is the maximum potential difference between two points of the battery when no current is flowing from the source in the case of an open circuit. In short, EMF is the cause, and Voltage or potential difference is the effect.

E or ε = W/Q … in Volts

Where:

• E or ε = Electromotive force energy in Volts
• W = Work done in Joules
• Q = Charge in Columbus

Ques. If the battery’s terminals are connected, calculate the current that will flow inside the battery at a voltage of 20 volts and an internal resistance of 5 ohms. Determine the battery’s terminal voltage.

Ans. Given:

• V = 20 V
• R = 5 ohms

V = IR

Substituting the values in the equation

I = V/R

   = 20/5

   = 4

So, the current is 4 A

Using the EMF formula for terminal voltage

E = V+Ir

Substituting the values the equation

V = E – Ir

    = 20 – 4×5

     = 20 – 20

     = 0

So, the terminal voltage is 0 V

Ques. Differentiate between emf and voltage.

Ans. Differences between EMF and voltage are specified below:

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