What size resistor should be connected across the terminals of a battery to produce a current of ?

Suppose that a circuit with a single resistor is connected to a battery. If of power is generated across this resistor, what is its resistance?

A battery is connected to a small heater with constant resistance . How much current flows through the heater?

The picture below shows the electron energy levels of a hydrogen atom.

If an electron is excited to the 5th energy level, how many different transitions can it make to return to ground state?

Use this circuit diagram for the next question.

What is the current traveling through the R2 resistor?