You will be given a definition of a task first, then an example. Follow the example to solve a new instance of the task.
Given a scientific passage and an answer, generate a question for the given answer.

Passage: A frameshift mutation is a deletion or insertion of one or more nucleotides that changes the reading frame of the base sequence. Deletions remove nucleotides, and insertions add nucleotides. Consider the following sequence of bases in RNA:. Answer: nucleotides.
Solution: A frameshift mutation is a deletion or insertion of one or more of what that changes the reading frame of the base sequence?
Why? The science passage defines frame mutation and the main compoment here is nucleotides. Hence the generated question is apt.

New input: Passage: Most of us have at least one device in our homes that guards our safety and, at the same time, depends on radioactivity to operate properly. This device is a smoke detector. A typical smoke detector contains an electric circuit that includes two metal plates about 1 cm apart. A battery in the circuit creates a voltage between the plates. Next to the plates is a small disk containing a tiny amount (0.0002 g) of the radioactive element americium. The radioactivity of americium ionizes the air between the plates, causing a tiny current to. Answer: voltage
Solution:
In a smoke detector, a battery in the electric circuit creates what between the metal plates?