NCERT Solution for Class 10 Science Chapter 12
Electricity
NCERT Books for Session 2020-2021
CBSE Board and UP Board
Exercises Questions
Page No-221
Questions No-13
A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 ohm resistance, which may be used separately, in series, or in parallel. What are the currents in the three cases?
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Given that: Potential difference V = 220 V and resistance of each coil R = 24 Ω
When the coil is used separately, the current in the coil is given by
𝐼=𝑉𝑅=220/24=55/6=9.16 𝐴
When the two coils are connected in series, the net resistance is given by
𝑅=𝑅1+𝑅2=24 Ω+24 Ω=48 Ω
Now, the current in the coil is given by
𝐼=𝑉𝑅=220/48=55/12=4.58 𝐴
When the two coils are connected in parallel, the net resistance is given by 1/𝑅=1/24+1/24=2/24=1/12 ⟹𝑅=12 Ω
Now, the current in the coil is given by
𝐼=𝑉𝑅=22012=553=18.33 𝐴
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Supply voltage, V = 220 V
Resistance of one coil, R = 24 Ω
(i) Coils are used separately
According to Ohm’s law,
V = I1R1
Where,
I1 is the current flowing through the coil
𝐼=𝑉𝑅=220/24=55/6=9.16 𝐴
Therefore, 9.16 A current will flow through the coil when used separately.
(ii) Coils are connected in series
Total resistance, R2 = 24 Ω + 24 Ω = 48 Ω
According to Ohm’s law,
V = I2R2
Where,
I2 is the current flowing through the series circuit
𝐼=𝑉𝑅=220/48=55/12=4.58 𝐴
Therefore, 4.58 A current will flow through the circuit when the coils are connected in series.
(iii) Coils are connected in parallel
Total resistance, R3 is given as
1/𝑅=1/24+1/24=2/24=1/12 ⟹𝑅=12 Ω
According to Ohm’s law,
V = I3R3
Where,
I3 is the current flowing through the circuit
𝐼=𝑉𝑅=22012=553=18.33 𝐴
Therefore, 18.33 A current will flow through the circuit when coils are connected in parallel.