Check sibling questions

(a) Write Joule’s law of heating.

(b) Two lamps one rated 100 W 220 V, and the other 60 W 220 V, are connected in parallel to electric mains supply. Find the currents drawn by two bulbs from the line, if the supply voltage is 220 V.

 

Answer:

(a)

Joule’s law of heating states that the heat produced in a conductor is directly proportional to 

(i) the square of  the current I through it, 

(ii) its resistance R and 

(iii) the time t , for which current is passed.

Therefore, the mathematical expression of Joule’s law of heating is: 

     H = I 2 Rt  

Where, 

  • H = Produced Heat  
  • I = Current flowing through the device  
  • t = Time of current flow  
  • R = Resistance of the appliance 

(b)

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Transcript

Question 7 (b) Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V?Given Potential difference = V = 220 V Power of lamp 1 = P1 = 100 W Power of lamp 2 = P2 = 60 W We need to find current through the circuit We know that In parallel combination current gets divided among the resistors But, Net current = Sum of current through individual resistors I = I1 + I2 Finding current We know that, Power = Voltage × Current P = V I ∴ I = 𝑃/𝑉 Lamp 1 I1 = 𝑃_1/𝑉 I1 = 100/220 I1 = 10/22 I1 = 5/11 A Lamp 2 I2 = 𝑃_2/𝑉 I2 = 60/220 I2 = 6/22 I2 = 3/11 ANet current I = I1 + I2 I = 5/11 + 3/11 I = 8/11 I = 0.73 A Net current through circuit is 0.73 A

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CA Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 12 years and a teacher from the past 16 years. He teaches Science, Economics, Accounting and English at Teachoo