In both circuits, the supply voltage is equal and remains unchanged. When the switch S is closed and the slider P of the sliding rheostat moves to the right, the brightness changes of the light bulbs L 1 and L2 are L 1, and the brightness of L2 is unchanged. Please design two circuit diagrams to meet the above requirements.

Analysis: In the first picture, two resistors are connected in series, and the sliding resistance of the connecting circuit (that is, the left part of point P) becomes larger, and the total resistance becomes larger, so the total current becomes smaller and L 1 becomes darker.

In the second picture, two resistors are connected in parallel, and the change of sliding resistance can be ignored. The voltage applied to both ends of the bulb is equal to the power supply voltage, and the voltage is unchanged, the branch current is unchanged, and the L2 brightness is unchanged.

As I am a first-class user, I have no right to upload pictures, so I can only draw with words.

-Lamp sliding rheostat-

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-power supply-switch-1 figure

-Light bulb-

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|-Sliding rheostat |

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-Power supply-switch-Figure 2

It's hard to draw little by little, hehe.