Chapter 3: Electricity

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Q
Electricity

Question:

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?

Answer:

(i) When the two coils A and B are used separately.

According to Ohm’s law,

V = IR

I = frac{V}{R}

Given: R = 24 Omega , V = 220 V

I = frac{220}{24}

I = 9.166 A

 

(ii) When the two coils are connected in series.

Total resistance, R = 24 + 24 = 48 Omega

V = 220 V {Given}

According to Ohm’s law,

V = IR

I = frac{V}{R}

I = frac{220}{48}

I = 4.58 A

 

(iii) When the two coils are connected in parallel.

Total resistance, frac{1}{R} = frac{1}{24} + frac{1}{24}

frac{1}{R} = frac{1 + 1}{24}

frac{1}{R} = frac{2}{24}

frac{1}{R} = frac{1}{12}

R = 12 Omega

V = 220 V {Given}

According to Ohm’s law,

V = IR

I = frac{V}{R}

I = frac{220}{12}

I = 18.33 A


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