The normal working voltage of a bulb is 4 V, and the resistance is 10 Ω. How large a resistor needs to be connected in series to connect it to a 12 V power supply To work properly

The normal working voltage of a bulb is 4 V, and the resistance is 10 Ω. How large a resistor needs to be connected in series to connect it to a 12 V power supply To work properly

20 ohm,
If the bulb works normally at 4 V and the resistance is 10 Ω, then the normal working current is 0.4A and the partial voltage of series resistance is 12 -- 4 = 8V

A lamp with 20 ohm resistance normally works at 10V, but only 12V. How to connect the lamp to the power supply

Connect it directly
Connect four resistors in series

There is a light bulb, its normal lighting filament resistance is 8.3 Ω, the normal lighting voltage is 2.5 V, if we have only 6 V power supply
In order to make the small bulb light normally, how much resistance should be connected?

Normal working current of bulb = 2.5/8.3a
The resistance requires a partial voltage of 6-2.5 = 3.5V
Resistance = 3.5 / (2.5 / 8.3) = 11.62 ohm

There is a normal working voltage is 24 V ground bulb, the resistance is 48 Ω. Connect it to 36 V power supply to light normally. Then what is the resistance
RT.

I amount = u amount / r = 24 △ 48 = 0.5A
R = (U-U) / I = (36-24) △ 0.5 = 24 Ω
A 24 Ω resistor should be connected in series