EM 5'8

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AL Physics
Turning torque (by I) Resisting torque (by
hairspring)
EM 5.8
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AL Physics
Concave magnet and small gap ? Constant Radial
field B ? magnetic force ? coil plane
(always) ? Constant Torque i.e. ? BANI sin
90o BANI
Resisting torque due to the hairspring in which
the restoring torque is directly proportional to
the angle turned. i.e. ? c ? where c is
the torisonal constant ( force constant) ?
is the angle turned
At Equilibrium, ? ? BANI c ? ? (NBA
/ c) I

• ? I if N, B, A and c are constant

? linear scale !!
EM 5.8
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AL Physics

• Current Sensitivity ? / I deflection per unit
  current
• ? / I NBA / c
• In order to increase the current sensitivity,
• no. of turn of coils ?,
• but the armature will be too bulky and the size
  of the air gap cannot be too small.
• Magnetic field in the air gap ?, i.e. Stronger
  magnet is used and the air gap should be as
  narrow as possible.
• area of the coil ?,
• but the coils will swing about its deflected
  position.
• Weaker hairspring,
• but if the opposition of the suspension is too
  weak (reading again take time).

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animation
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Smoother and Faster
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EXERCISE M.C. 17, 18
5 minutes
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EM 5.8
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animation
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animation
EM 5.8