Electric Power

Watt represents the unit of electric power. Power in mechanics is defined as the rate of work or energy transfer, while electric power is the rate of electric energy transfer. In other words, electric power is the electric energy used up per unit of time. 

Mathematically, electric power is formulated as follows.

 P=W/t 

In which: 

P = Electric power (watt; W) 

W = Electric energy (joule; J) 

t = Time interval (second; s) 

One watt (1 W) is energy of 1 joule released in time interval of 1 second. 

Another unit that is often used to represent electric energy is kW (kilowatt) or MW (mega watt) 

1 kW = 1000 W

1 MW= 1000000 W 

Example: 

In your house a circuit breaker or often called fuse is set in an electric circuit the voltage of which is 220 V. If the electric current that flows is 3 A, what is the power of the fuse? 

Solution 

Given that 

V = 220 V 

I = 3 A 

Asked: P….? 

Answer: P = VI = 220 V x 3 A = 660 W 

Thus, the power of the fuse is 660 W. 

Reference:

Irawan, Etsa Indra dan Sunardi. 2008. Pelajaran IPA-Fisika Bilingual untuk SMP/MTs. Kelas IX. Bandung: CV.Yrama Widya.