A knob on a touch panel includes a rotary wheel, a common pad, at least one sensing pad, a plurality of connectors and a conductive ring. The rotary wheel is mounted on the touch panel. The common pad is deployed on the touch panel. The at least one sensing pad is deployed on the touch panel. Each of the plurality of connectors is coupled between the rotary wheel and one pad among the at least one sensing pad and the common pad, to control each of the at least one sensing pad to be coupled to the common pad or not through the rotary wheel according to an operation of the knob. The conductive ring is deployed on a surface of the rotary wheel, to detect a touch object.