Answer:
By combining the voltage drop across the rheostat with the voltage drop across the internal resistance, the emf of the battery can be calculated. The voltage drop across the rheostat in this scenario is 50 volts when the rheostat is set to 10 ohms and the ammeter reads 5 amperes. Ohm's law is used to compute the voltage drop across the internal resistance (0.2 ohms * 5 amperes = 1 volt). We can calculate the battery's emf by adding these two volts, which give us the answer 51 volts.