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 VResistance of one coil,

R =24 Ω(i) Coils are used separately

According to Ohm’s law,

V = I

_{1}R_{1}Where,

I

_{1 }is the current flowing through the coil𝐼=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 = I

_{2}R_{2}Where,

I

_{2}is the current flowing through the series circuit𝐼=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, R

_{3}is given as1/𝑅=1/24+1/24=2/24=1/12 ⟹𝑅=12 Ω

According to Ohm’s law,

V = I

_{3}R_{3}Where,

I

_{3 }is the current flowing through the circuit𝐼=𝑉𝑅=22012=553=18.33 𝐴

Therefore, 18.33 A current will flow through the circuit when coils are connected in parallel.