What voltage was required for an incandescent lamp with a resistance of 20 ohms to generate a current of 0.1.

According to Ohm’s law, the current in an incandescent lamp will be directly proportional to the voltage across the lamp and inversely proportional to the resistance of the lamp.
I = U / R, where I is the current in the lamp (I = 0.1 A), U is the voltage across the lamp (V), R is the resistance of the lamp (R = 20 ohms).
Let’s express and calculate the voltage across the lamp:
U = I * R = 0.1 * 20 = 2 V.
Answer: The lamp needed a voltage of 2 V.