More practice questions

4. Q4. Assertion: for a given power delivered, the power wasted in transmission cables falls as the transmission voltage rises. Reason: the current needed falls as 1/V, and the loss is I^²R_c. Are both true, and does the reason explain the assertion?

   Show answerHide answer

   Both are true, and the reason explains the assertion: P_c = I^²R_c = P^²R_c/V^² (NCERT Eqs. (3.34)–(3.35), page 93).

5. Q5. Two bulbs rated 100 W and 60 W at 220 V are compared. Which has the larger resistance?

   Show answerHide answer

   R = V^²/P, so at the same rated voltage the 60 W bulb has the larger resistance: 220^²/60 ≈ 807 Ω against 220^²/100 = 484 Ω (NCERT Eq. (3.33), page 93).

6. Q6. A resistor of 20 Ω carries 0.50 A for 10 minutes. How much heat is produced?

   Show answerHide answer

   W = I^²Rt = 0.50^² × 20 × 600 = 3000 J (NCERT Eqs. (3.31) and (3.33), pages 92–93).