Connect a dry battery, a small electric bead with a working voltage of 2.5V and a pencil lead with a length of 7cm to form a circuit as shown in the figure. Adjust the length of the pencil lead in the circuit just so that the small electric bead does not light up. Now you can strike a match and heat the pencil lead, and the small electric bead will light up later. Once the match goes out, the small electric bead will go out slowly. Here, the flame Like a switch, why can the flame play such a role?

Connect a dry battery, a small electric bead with a working voltage of 2.5V and a pencil lead with a length of 7cm to form a circuit as shown in the figure. Adjust the length of the pencil lead in the circuit just so that the small electric bead does not light up. Now you can strike a match and heat the pencil lead, and the small electric bead will light up later. Once the match goes out, the small electric bead will go out slowly. Here, the flame Like a switch, why can the flame play such a role?

A: when the pencil lead is heated, the temperature increases and the resistance decreases, but the power supply voltage remains unchanged, so the current in the circuit increases and the light turns on. When the pencil lead is stopped, the temperature decreases and the resistance increases, so the current in the circuit decreases and the light turns off

There are two dry batteries, one switch, two small bulbs, one ammeter and one voltmeter, and several wires. Please design a circuit
Requirements: two bulbs in series, ammeter and voltmeter respectively measure the current and voltage of bulb L1

Battery ammeter
Basic voltmeter
┃ ┃ ┃ ┃
━┻ bulb L1 ┻━ bulb L2 ━
In series circuit, the current is equal, so no matter where the ammeter is placed, the current is measured
A voltmeter connected in parallel with L1 measures L1 voltage
It's purely self created,:)