Given a 10 ohm resistance, connected in series with a small bulb, the supply voltage is 6 V, calculate the resistance of the small bulb

A voltmeter is also needed to know the on resistance of the bulb
After the circuit is connected and powered on, the bulb lights up. At this time, use a voltmeter to measure the voltage at both ends of the 10 ohm resistor, and then use the voltage division method to calculate the bulb resistance
If the voltage at both ends of the resistor is 2V, the voltage at both ends of the bulb is 6v-2v = 4V
And the series circuit current is equal. So the bulb resistance is: X
4V / x = 2V / 10 Ω
Then x = 20 Ω
The same applies to other values

What is the working current of a 12V DC horn with 4 ohm resistance and 10W power?

Very simple, 12 / 4 = 3A! If you want to calculate the peak current, it is related to the amplitude of the audio signal

There is a bulb with a resistance of 12 ohm and a maximum voltage of 6 v. if you want to connect it to an 8 V power supply, what should you do?

Connect three diodes. Because the resistance of the bulb is different when it is on or off, the 12 ohm resistance here is not sure whether it is on or off, but two lamps in series will never burn, but the brightness is a problem. The voltage drop of the diode is about 0.7, The other is that this bulb is connected in series with (three parallel connected bulbs of the same model) to ensure that this one is on, but the other three are basically off

R1 = 5 ohm, R2 = 20 ohm. When the switch is closed, the current indication is 0.4A. Calculate the equivalent resistance of two resistors in series in the circuit
R1 = 5 ohm, R2 = 20 ohm. When the switch is closed, the current indication is 0.4A. Calculate the equivalent resistance of two resistors in series in the circuit and the voltage indication

25 Ohm 10 V

Given a 10 ohm resistance, connected in series with a small bulb, the supply voltage is 6 V, calculate the resistance of the small bulb