The basic structure and regulation of the 9th grade physical sliders are often applied to the knowledge point sliders
Sliding transformers regulate resistance by changing the length of the wire in the circuit, the core structure of which consists of fixed lines at both ends of the wire (e. G., a, c in the video) and actionable links to slides (e. G. B in the video). Key reconciling conditions: the two poles must be selected to access the circuit “one at a time”, and if the two poles are connected (e. G. A, c), the entire circuit is fixed and the slides are unregulated; if the two poles are taken, the connection is zero, which cannot be reconciled。
Typical error analysis
Title: when the slider connects to the light bulb, the slide adjusts the lightness of the light bulb
Option a: slide transformers are linked to light bulbs
Reason for error: the circuits are working independently and do not affect each other, and the slide transformer cannot change the current of the feeder in which the light bulb is located, and therefore the lightness of the light bulb cannot be regulated。
Option b: darken the slider bulb by connecting a, c to the circuit
Reason for error: a,c are fixed lines at both ends of the electrical barrier, the entire electrical barrier is fully connected to the circuit at the time of accessa,c and the resistance is fixed. No matter how the slider rotates, the total circuit resistance remains the same, the current is the same, and the light bulb is the same, so this option is wrong。
Option c: lighten a, b access circuits, clockwise rotation slides
Reason for error: when a,b accesses the circuit, the electrical resistance to the circuit is part of a to slideb. Clockwise rotates sliders, slides move down, a to b wire length becomes longer and resistance increases; according to om's law (i=frac{u}r}, electrical current becomes smaller in circuits, the real power of light bulbs (p=i^2r) decreases, and the brightness becomes dark, so this option is wrong。
Option d: access to circuits b, c, more fine (lower cross-section), rotate slides at the same speed as clockwise, and light bulbs change more significantly
Correct reason:
Impact factors of resistance: the size of resistance is related to material, length, area of cross-section (the smaller the area of cross-section when the material and length are the same, the greater the resistance). When wires are fined, the unit length is increased. (c) resistance change analysis: the total resistance change is greater when the same rotational distance (i. E., the length change is the same) is increased in units of length. The effect of brightness changes: the greater the resistance changes, the greater the current changes in the circuit (based on (i=frac{u}r})) and the greater the change in the real power of the light bulb (p=i^2r). (b) the effect factor (materials, length, cross-section area) on resistance can have a direct effect on the sensitivity of resistance changes, the smaller the cross-section area, the greater the unit length resistance, the more significant the change in electrical resistance in the same operation and the greater the change in the state of the element in the circuit (e. G. Light bulb)。
