Step-by-step NCERT solutions for Moving Charges and Magnetism (Chapter 4, CBSE Class 12 Physics) — every question and answer worked out in full, not just the final result. You can also read the Moving Charges and Magnetism textbook chapter.
All 13 questions in Moving Charges and Magnetism are solved in the PDF. Here's what's inside, exercise by exercise:
3 questions from Moving Charges and Magnetism, solved step by step.
Exercises
Given: N = 100 turns, R = 8.0 cm = 0.08 m, I = 0.40 A
Formula for magnetic field at the centre of a circular coil:
B = µ₀NI / (2R)
B = (4π × 10⁻⁷ × 100 × 0.40) / (2 × 0.08)
B = (4π × 10⁻⁷ × 40) / 0.16
B = (160π × 10⁻⁷) / 0.16
B = 1000π × 10⁻⁷ T
B = π × 10⁻⁴ T ≈ 3.14 × 10⁻⁴ T
Answer: B ≈ 3.14 × 10⁻⁴ T (= π × 10⁻⁴ T)
Exercises
Given: I = 35 A, r = 20 cm = 0.20 m
For a long straight wire, by Ampere's circuital law:
B = µ₀I / (2πr)
B = (4π × 10⁻⁷ × 35) / (2π × 0.20)
B = (4 × 10⁻⁷ × 35) / (2 × 0.20)
B = (140 × 10⁻⁷) / 0.40
B = 350 × 10⁻⁷ T
B = 3.5 × 10⁻⁵ T
Answer: B = 3.5 × 10⁻⁵ T
Exercises
Given: I = 50 A (flowing north to south = southward), r = 2.5 m (point to the east)
Magnitude:
B = µ₀I / (2πr) = (4π × 10⁻⁷ × 50) / (2π × 2.5)
B = (4 × 10⁻⁷ × 50) / (2 × 2.5) = 200 × 10⁻⁷ / 5
B = 4.0 × 10⁻⁶ T
Direction using right-hand rule:
Set up coordinates: x = east, y = north, z = upward.
Current direction: south (−y). Point is to the east (+x) of the wire.
B ∝ (current direction) × (radial direction from wire to point)
= (−ŷ) × (+x̂) = −(ŷ × x̂) = −(−ẑ) = +ẑ
B is directed vertically upward at the east point.
Physical check: wrap right hand around wire with thumb pointing south; at the east side, fingers point upward. Confirmed.
Answer: B = 4.0 × 10⁻⁶ T, directed vertically upward
All 13 questions in Moving Charges and Magnetism are solved step by step in the Solutions PDF above.
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