an electric iron power rating is 1.2 kw how much does it cost if it is used for 2 hours and the changes for 1 unit electricity is rupees 7
Answers
Power of the electric iron P=2 kW
Time for which the iron is operated daily t=2 h
Daily energy consumption E
daily
=Pt=2 kW×2 h=4 kWh
Total energy consumed in one week E
week
=7×E
daily
=7×4=28 kWh
Total cost =Rs.4.25×E
week
=Rs.4.25×28=Rs.119
Answer:
Electric energy depends on both the voltage involved and the charge moved. This is expressed most simply as PE = qV, where q is the charge moved and V is the voltage (or more precisely, the potential difference the charge moves through). Power is the rate at which energy is moved, and so electric power is
P
=
P
E
t
=
q
V
t
.
Recognizing that current is I = q/t (note that Δt = t here), the expression for power becomes
P = IV
Electric power (P) is simply the product of current times voltage. Power has familiar units of watts. Since the SI unit for potential energy (PE) is the joule, power has units of joules per second, or watts. Thus, 1 A ⋅V= 1 W. For example, cars often have one or more auxiliary power outlets with which you can charge a cell phone or other electronic devices. These outlets may be rated at 20 A, so that the circuit can deliver a maximum power P = IV = (20 A)(12 V) = 240 W. In some applications, electric power may be expressed as volt-amperes or even kilovolt-amperes (1 kA ⋅V = 1 kW). To see the relationship of power to resistance, we combine Ohm’s law with P = IV. Substituting I = V/R gives P = (V/R)V=V2/R. Similarly, substituting V = IR gives P = I(IR) = I2R. Three expressions for electric power are listed together here for convenience:
P
=
IV
P
=
V
2
R
P
=
I
2
R