Q17 of 19 Page 12

A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 Ω resistance, which may be used separately, in series, or in parallel. ( CBSE 2015, 2007)

Case (i): When each coil is used separately

Here, Potential difference, V = 220 V


Resistance of a coil, R = 24


Using Ohm’s Law, the current passing through one coil is given as,



Case (ii) Calculation of current when the two coils are connected in series


When the two coils of 24 each are connected in series, then their combined resistance will be R= 24 + 24 = 48


Potential difference, V = 220 V


And, Resistance, R = 48 Q


Again, Current passing through both coils connected in series, is given as:



Case (iii) Calculation of current when the two coils are connected in parallel


When the two coils of 24 each are connected in parallel, then their combined resistance will be given as:



Here, Potential difference, V = 220 V


Resistance of two coils in parallel connection, R = 12 (Two coils in parallel)


Now, Current, I =

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