Loading resistance, **voltage drop** on it, force of the current passing through it and the power allocated on it are the physical quantities connected among themselves. Knowing any two from them, it is possible to calculate two remained.

## Instruction

1. Regardless of which parameters are given in a statement of the problem, transfer them to the SI system.

2. If in a condition resistance of loading and the power allocated on it are given, be guided by the following reasons: R=U/I where R is resistance, Ohm, U is tension, In, I - current, A.P=UI where P - power, W, U - voltage drop, In, I - current, And. From this it follows that P=I^2*R, that is, I^2=P/R, or I=sqrt(P/R). Therefore, U=R(sqrt(P/R)) or, after simplification of expression, U=sqrt(P)*sqrt(R) where U is required voltage drop on loading, In, R is resistance, the Ohm, P is power, W.

3. Much simpler case arises if it is necessary to find falling tension, knowing the power and current. It will not be required to transform expression therefore at once use the following formula: U=P/I where U is required voltage drop, In, P is the power allocated on loading, W, I - force of the current passing through loading, And.

4. If resistance of loading and the current passing through it are known, on it also calculate voltage drop in one action: U=IR where U is required voltage drop, In, I - the current passing through loading, And, R - resistance of loading, Ohm.

5. Besides the most often found tasks given above, in textbooks also others in which it is necessary to learn voltage drop on a piece of the long uniform core made of the material having high resistance come across. For this purpose in the beginning calculate voltage drop on all length of a core (if it is not given in a statement of the problem initially). After that subtract the friend from the friend horizontal coordinates of points between which voltage drop needs to be defined.

6. Divide tension on all length of a core into its length then increase by the piece length calculated by you, and you receive voltage drop between points. Similar dividers meet in the equipment bestransformatorny food and are used as switches of mains voltage - in this case the efficiency and safety is sacrificed to simplicity of a design.

7. Having finished calculations, if necessary transfer result to units, convenient for its representation: volts, millivolts, kilovolts, etc.