Two resistors with resistances of 2 and 4 ohms are connected in series.

Two resistors with resistances of 2 and 4 ohms are connected in series. The voltage across the first resistor is 8 V. What is the voltage across the second resistor?

R1 = 2 ohms.
R2 = 4 ohms.
U1 = 8 V.
U2 -?
For a series connection of resistors, the following formulas are valid: R = R1 + R2, I = I1 = I2, U = U1 + U2.
Let’s write Ohm’s law for the first resistor: I1 = U1 / R1.
Let’s write Ohm’s law for the second resistor: I2 = U2 / R2.
Since I = I1 = I2, then U1 / R1 = U2 / R2.
U2 = U1 * R2 / R1.
U2 = 8 V * 4 ohms / 2 ohms = 16 V.
Answer: the voltage across the second resistor U2 = 16 V.