# What is the relation between Electrical and Thermal Units?

### Relation between Electrical and Thermal Units:

In this short post let us discuss about the relation between Electrical and Thermal Units.

#### Joule's Law of Electric Heating:

The amount of work done or energy required to maintain a current of 1 amperes passing through a resistance of R ohms for 1 second is

Workdone = (I^{2}R).t joules

= VI.t joules [We know that V = IR as per Ohms law]

= V^{2}t/R joules [ As I = V/R ]

= W.t joules [As V^{2}/R = W ]

The work done is converted into heat H = Work done/ Mechanical equivalent of heat

H = W.D / J

where J = 4200 joules/K cal.

H = (I^{2}R.t / 4200 ) K cal.

= (VI.t / 4200 ) K cal.

= (V^{2}t / R x 4200 ) K cal.

= (W.t / 4200 ) K cal.

Also 1KWH = 860K cal.

#### Relation between Electrical and mechanical units:

1 horse power ( metric) = 75 m-kg/sec.

ie,

1 horse power ( metric) = 75 x 9.81

ie,

1 horse power ( metric) = 735.5 J/sec.

Therefore

**1 HP = 735.5 watts.**

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I'm a first year apprentice Electrician, and everything we have been given to study and base our calculations on says that 1 HP = 746 W. You say it's 735.5 and now I'm confused again