P = U ² / r

**if U = u**

P = p: The surface charge density (W / cm ²) is preserved

P = U ² / U ² re = / 2r

**if U = u**

P = p / 2: The surface charge density (W / cm ²) is divided by 4

P = U ² / re = 2.U ² / r

re = r / 2

**s****i** **U = u**

P = 2p: The surface charge density (W / cm ²) is preserved

P = 3.U ² / r

**if U = u**

P = 3p: The surface charge density (W/cm2) is preserved

**if U = \ / ¯ 3u**

P = 9p: The surface charge density (W/cm2) is multiplied by 3 (it may destroy the resistance)

**if U = u / \ / ¯ 3**

P = p: The surface charge density (W/cm2) is divided by 3

P = 3.U ² / r = U ² / r

**if U = u \ / ¯ 3 **

P = 3p: The surface charge density (W/cm2) is preserved

**if U = u**

P = p: The surface charge density (W/cm2) is divided by 3

**if U = u / \ / ¯ 3**

P = p / 3: The surface charge density (W/cm2) is divided by 9

P = 3.U ² / re = U ² / re

P = 3.U ² / Re

Resistors r1, r2, ... rn in series

Resistors r1, r2, ... rn parallel

Re = r1 + r2 + ... + Rn

If r1 = r2 = ... = Rn = r **Re = n.r**

1 / Re = 1 / r1 + 1/r2 + ... 1 / rn

If r1 = r2 = ... Rn = r = 1 / Re = n.1 / r** Re = r / n**

**NOTE: ***If p is the power of the heater at the rated voltage u and U the voltage, the total power P and the drying surface (W / cm ²) are equal to:*