When the above circuit is closed, the current flowing through it is 0.5 A. Under these conditions, the voltage across the battery terminals (which has an emf of 10 V) is 8 V.

a) What is the internal resistance of the battery?

Answer: The decrease in voltage at the battery terminals is emf - V = 10 - 8 = 2 volts. Using Ohm's Law, knowing that the current is 0.5 amperes, we get r = 2/0.5 = 4 Ω.

b) What would happen to the reading on the voltmeter if the resistance R decreased?

Answer: The voltmeter reading is inversely proportional to the current flowing through the battery. Decreasing the value of R will cause a greater current to flow, and so the reading on V will decrease.