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. What are the currents in the three cases?

NCERT Question 13 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. What are the currents in the three cases?
Potential difference = 220 V
Resistance of each wire = 24 Ω
By Ohm’s law,
V = I R
∴ I = 𝑉/𝑅
Case I - When either (only 1) is used
R = 24 Ω
Now,
I = 𝑉/𝑅
I = 220/24
I = 55/6
I = 9.2 A
Case II - When two wires are connected in series
We know that
In series combination
equivalent resistance is given by
RS = R1 + R2
RS = 24 + 2 4
RS = 48 Ω
Now,
I = 𝑉/𝑅_𝑆
I = 220/48
I = 110/24
I = 55/12
I = 4.6 A
Case III - When two wires are connected in parallel
We know that
In parallel combination
equivalent resistance is given by
1/𝑅_𝑝 = 1/𝑅_1 + 1/𝑅_2
1/𝑅_𝑝 = 1/24 + 1/24
1/𝑅_𝑝 = 2/24
1/𝑅_𝑝 = 1/12
Rp = 12 Ω
Now,
I = 𝑉/𝑅_𝑝
I = 220/12
I = 110/6
I = 55/3
I = 18.3 A

CA Maninder Singh is a Chartered Accountant for the past 13 years and a teacher from the past 17 years. He teaches Science, Economics, Accounting and English at Teachoo

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