**Q.1. A circular coil of wire consisting of 100 turns, each of radius 8.0 cm**

**carries a current of 0.40 A. What is the magnitude of the magnetic**

**field B at the centre of the coil ?**

**Sol. Given , N = 100 , r= 0.08m , I= 0.4A**

**B = 10 ^{−7}×2×3.14×0.4×100/0.08**

**Q2. A long straight wire carries a current of 35 A. What is the magnitude**

**of the field B at a point 20 cm from the wire ?**

**Sol. By formula ,**

**B = 10 ^{−7}×2×35/0.20**

**= 3.5 × 10 ^{−5} T**

**Q3. A long straight wire in the horizontal plane carries a current of 50 A**

**in north to south direction. Give the magnitude and direction of B**

**at a point 2.5 m east of the wire.**

**Sol. By formula ,**

**B = 10 ^{−7}×2×50/2.5**

**B = 4 × 10 ^{−6} T**

**Q4. A horizontal overhead power line carries a current of 90 A in east to**

**west direction. What is the magnitude and direction of the magnetic**

**field due to the current 1.5 m below the line ?**

**Sol. By formula ,**

**B = 10 ^{−7}×2×90/1.5**

**B = 1.2×10 ^{−5} T**

**Q5. What is the magnitude of magnetic force per unit length on a wire**

**carrying a current of 8 A and making an angle of 30º with the**

**direction of a uniform magnetic field of 0.15 T ?**

**Sol. By formula , F = IlBsinθ**

**F = 8×1×0.15×Sin30º**

**F = 0.6 N/m**