Traditional Culture Encyclopedia - Photography and portraiture - Existing: a small light bulb with a rated voltage of U0, a power supply (voltage greater than U0), two sliding rheostats with a maximum resistance of 20Ω (small

Existing: a small light bulb with a rated voltage of U0, a power supply (voltage greater than U0), two sliding rheostats with a maximum resistance of 20Ω (small

Connect the wiring according to the diagram below

First move the switch to the 1 position, adjust the rheostat above so that the voltmeter reads U0, keep the resistance above unchanged, and turn the switch to 2, adjust the rheostat below so that the voltmeter reads U0 again. Then use a scale to measure the resistance of the sliding rheostat. This resistance is the resistance of the light bulb.

NextP=U*U/R