The terminal voltage of the battery is observed to fall when the battery supplies a current to an external resistor. Which of these are required to calculate the change in voltage
1. Electromotive force and internal resistance of the battery
2. Electromotive force and current
3. Current and internal resistance of the battery
4. Current and external resistance
Explain your answer.

Question

The terminal voltage of the battery is observed to fall when the battery supplies a current to an external resistor. Which of these are required to calculate the change in voltage
1. Electromotive force and internal resistance of the battery
2. Electromotive force and current
3. Current and internal resistance of the battery
4. Current and external resistance
Explain your answer.

anonymous · Answer

In my opinion, the correct answer would be nº4.
You're viewing a closed circuit that is composed of a battery and an resistor. The voltage drop is due to the energy lost in the resistor, so if you apply the Ohm's law you'll see a different value for the electromotive force (or voltage), comparing the open and closed circuit..
$$U=RI$$

radar · Answer

Knowing the internal resistance of the battery and the current would allow you to calculate the amount of voltage sag (change in voltage).  The viewer would know the terminal voltage as he observes the sag.

naveenbabbar · Answer

Use V= E-Ir or E-V=Ir
Here E is emf, V is the potential drop and r is the internal resistance. So from this formula it is clear that you need to know I and r. So (3) option is right.