What allows the bimetallic coil to turn on or off a heating or cooling system? The two metals contract the same amount. The thermostat is set at a particular temperature. The two metals expand differently. The coil comes in contact with air.

The two metals expand differently.

Explanation:

The bimetallic strip has two metal strips positioned like a bridge, these strips connect the electrical circuit to the heating system. When these strips are linear or "down" they allow the electricity to move through the circuit to the heating system to turn the heat on. When the strips are "up" the disconnect the electricity flow, thus turning the heating system off, thus the room becomes cool/cold.

beta is electron from nucleus

something from nucleus has changed, but charge must be same for cons of charge