Q4. An ideal transformer draws 2.0 A in its primary and delivers 0.40 A from its secondary. Find Ns/Np and say whether it steps the voltage up or down.
Is/Ip = Np/Ns, so Ns/Np = Ip/Is = 2.0/0.40 = 5. The secondary has 5 times the turns, so it steps the voltage up 5 times while the current falls 5 times (NCERT Eqs. (7.35)–(7.36), page 195).
Q5. An ideal step-up transformer raises 230 V to 4600 V. If the primary carries 20 A, what is the secondary current, and what is the turns ratio Ns/Np?
Ns/Np = 4600/230 = 20, so Is = Ip × Np/Ns = 20 × 1/20 = 1.0 A (NCERT Eq. (7.36), page 195).
Q6. Which nonideal transformer effect is reduced by (a) thick wire, (b) a laminated core, (c) winding one coil over the other?
(a) The resistance (I2R) loss in the windings. (b) Eddy-current loss. (c) Flux leakage (NCERT pages 195–196).
Q7. A transformer with an efficiency of 90% supplies 360 W at 12 V from a 240 V rms mains with unity input power factor. Find the primary current.
The input power is 360/0.90 = 400 W, so Ip = 400/240 ≈ 1.7 A (reasoned from NCERT page 195).