These devices are only concerned of transmitting and receiving bits i.e., signals corresponding to 1s and 0s. Repeaters and Hubs are examples of physical layer devices.
Repeaters are used to increase cabling lengths. LAN cable segments have physical maximum lengths beyond which the signals on them fades. Repeaters amplify these signals so that different cable segments can be interconnected to extend the physical size of the LAN.
These are multiport devices which split and forward the signals into all outgoing ports. Passive hubs only split and forward the signal while active hubs amplify the signal before forwarding it to outgoing ports.
Wired networks require cabling. Different cabling types in existence today are coaxial, twisted pair and fibre optic.
Coaxial cables were used in older Ethernet variants but they are no longer used in LANs.
Twisted pair is the most popular cable type today. Category 5 twisted pair cable is used for fast Ethernet (100Mbps) and Gigabit Ethernet (1Gbps).
Fibre optic cables have high data rates and these are used in gigabit Ethernet and 10gig Ethernet but they are expensive compared to twisted pair.