A simple circuit, using a battery, switch, wires and bulb can be altered by adding more or less components.

Add more batteries - the bulb gets brighter

The higher the voltage is of a battery, the more powerful it is.

Using a higher voltage battery will also make a buzzer louder.

Be careful - using a higher voltage will destroy the bulb.

This is the same for buzzers as they get louder.

Be careful though - too many batteries will destroy the bulb.

Use higher voltage batteries - the bulb gets brighter

Add more bulbs - the bulbs get dimmer

Several buzzers would each buzz more quietly than just one.

Several motors would each turn more slowly than just one.