Two coaxial solenoids of different radii carry current I in the same direction. Let $stack straight F subscript 1 with rightwards arrow on top$ be the magnetic force on the inner solenoid due to the outer one and $stack straight F subscript 2 with rightwards arrow on top$ be the magnetic force on the outer solenoid due to the inner one. Then:

$stack straight F subscript 1 space with rightwards arrow on top equals stack straight F subscript 2 space with rightwards arrow on top equals space 0$
$stack straight F subscript 1 with rightwards arrow on top$ is radially inwards and $stack straight F subscript 2 with rightwards arrow on top$ is radially outwards
$stack straight F subscript 1 with rightwards arrow on top$ is radially inwards and $stack straight F subscript 2 with rightwards arrow on top$ =0
$stack straight F subscript 1 with rightwards arrow on top$ is radially outward and $stack straight F subscript 2 with rightwards arrow on top$ =0

Solution

stack straight F subscript 1 space with rightwards arrow on top equals stack straight F subscript 2 space with rightwards arrow on top equals space 0

Consider the two coaxial solenoids. Due to one of the solenoids magnetic field at the centre of the other can be assumed to be constant

Due to symmetry, forces on upper and lower part of the solenoid will be equal and opposite and hence resultant is zero.
Therefore option (a) is correct.

Some More Questions From Moving Charges And Magnetism Chapter

Two moving coil meters, M₁ and M₂ have the following particulars:
R₁ = 10 Ω N₁ = 30,
A₁ = 3.6 x 10^–3 m², B₁ = 0.25 T
R₂ = 14 Ω; N₂ = 42,
A₂ = 1.8 x 10^–3 m², B₂ = 0.50 T
(The spring constants k are identical for the two meters).
Determine the ratio of (a) current sensitivity and (b) voltage sensitivity of M₂ and M_1.

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Moving Charges And Magnetism

Some More Questions From Moving Charges And Magnetism Chapter

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