# Physics Class 12 NCERT Solutions: Chapter 6 Electromagnetic Induction Part 8

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Q: 17. A line charge per unit length is lodged uniformly onto the rim of a wheel of mass an radius. The wheel has light non-conducting spokes and is free to rotate without friction about its axis (Fig. 6.22). A uniform magnetic field extends over a circular region within the rim. It is given by,

What is the angular velocity of the wheel after the field is suddenly switched off?

Answer:

Line charge per unit length

Where,

Distance of the point within the wheel

Mass of the wheel

Radius of the wheel

Magnetic field,

At distance r, the magnetic force balanced by the centripetal force i.e.,

Where,

Linear velocity of the wheel

For, we get