Two circular coils made of similar wires but of radius 20 cm and 40 cm are connected in parallel. The ratio of the magnetic fields at their centre is:
Correct answer: B. 1:4
- A. 4:1
- B. 1:4
- C. 2:1
- D. 1:2
Explanation
For a circuar coil, the magnetic field at the centre is B = μoI/ 2r, where I is the current and r is the radius. In parallel connection, the voltage across both coils is the same, so I ∝1/R and R ∝r (for similar wires). Thus, I ∝ 1/r. The field ratio becomes.B1/B2= (I1/I2, r2/r1)2= (40/20)2= 1/4.
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Magnetic flux density and magnetic flux describe the strength of a magnetic field and the field passing through a surface. A charged particle moving through a magnetic field experiences a force perpendicular to its velocity and may follow circular or helical motion, depending on the angle between velocity and field.
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