Answer the following question given this paragraph: 

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.


Q: In a smoke detector, a battery in the electric circuit creates what between the metal plates?

 Choices:

- magnetism

- hydrogen

- cooling

- voltage

A:
voltage
