Final answer:
Expansion slots in modern computers allow additional cards to be connected to the motherboard that interface with peripheral devices.
Step-by-step explanation:
The purpose of expansion slots in modern computers is to allow additional cards to be connected to the motherboard that interface with peripheral devices. These expansion cards can include a variety of devices such as sound cards, graphics cards, network cards, and USB controllers. The expansion slots on the motherboard provide the necessary connections for these cards to communicate with the other components of the computer system.