Science
(a) An electric iron consumes energy at a rate of 880 W when heating is at the maximum rate and 330 W when the heating is at the minimum. If the source voltage is 220 V, calculate the current and resistance in each case.
(b) What is heating effect of electric current ?
(c) Find an expression for the amount of heat produced when a current passes through a resistor for some time.
Household Circuits
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Answer
(a) Given,
Power (P) = 880 W [when heating is at the maximum rate ]
Power (P) = 330 W [when heating is at the minimum rate ]
Voltage (V) = 220 V
Case I : When heating is at the maximum rate
We know,
P = VI
Substituting we get,
880 = 220 x I
I = = 4 A
From V = IR
Substituting we get,
220 = 4 x R
R = = 55 Ω
Hence, when heating is at the maximum rate, I = 4 A and R = 55 Ω
Case II : When heating is at the minimum rate
Substituting we get current (I)
330 = 220 x I
I = = = 1.5 A
Substituting we get resistance (R),
220 = 1.5 x R
R = = 1.46 Ω
Hence, when heating is at the minimum rate, I = 1.5 A and R = 1.46 Ω
(b) When the electric circuit is purely resistive, that is, a configuration of resistors only connected to a battery; the source energy continually gets dissipated entirely in the form of heat. This is called heating effect of electric current.
(c) H = I2Rt where
This is known as Joule's law of heating.
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