Home
Class 12
PHYSICS
Take a strong cylindrical electromagnet ...

Take a strong cylindrical electromagnet connected to AC source and place a light metallic disc at the top of it. When the current is switched 'on', the disc is thrown up in the air.
a. Why does the disc go up?
b. How is the repulsive force produced?

Text Solution

Verified by Experts

a. Induced currents are produced in the disc which acts in such a manner that it opposes the increase of magnetic flux through it. As a result the disc is thrown up.
b. When the circuit is switched on, the current starts growing through the solenoid. As the current grows, the magnetic lines along the axis of the solenoid and hence magnetic flux through the disc also increases from zero to some finite value. Induced currents are produced in the disc which opposes the increase of magnetic flux through it. Hence the disc is thrown up.
Promotional Banner

Topper's Solved these Questions

  • ELECTROMAGNETIC INDUCTION

    NEW JOYTHI PUBLICATION|Exercise CONTINUOUS EVALUATION (ASSIGNMENTS)|2 Videos

  • ELECTROMAGNETIC INDUCTION

    NEW JOYTHI PUBLICATION|Exercise PREVIOUS YEAR QUESTIONS|2 Videos

  • ELECTROMAGNETIC INDUCTION

    NEW JOYTHI PUBLICATION|Exercise PRACTICE PROBLEMS FOR SELF ASSESSMENT|3 Videos

  • ELECTRIC CHARGES AND FIELDS

    NEW JOYTHI PUBLICATION|Exercise Competitive Exam Corner|20 Videos

  • ELECTROMAGNETIC WAVES

    NEW JOYTHI PUBLICATION|Exercise COMPETITIVE EXAM CORNER|16 Videos

Similar Questions

Explore conceptually related problems

Figure shows a metal rod PQ resting on the smooth rails AB and positioned between the poles of a permanent magnet. The rails, the rod and the magnetic field are in three mutually perpendicular directions. A galvonometer G connects the rails through a switch K. Length of rod = 15 cm, B = 0.50 T, resistance of the closed loop containing the rod = 9.0mOmega . Assume the field to be uniform. a. Suppose K is open and the rod is moved with a speed of 12cms^(-1) in the direction shown. Give the polarity and magnitude of the induced emf. b. Is there an excess charge built up at the ends of the rods when K is open? What if K is closed? c. With K open and the rod moving uniformly, there is no net force on the electrons in the rod PQ eventhough they do experience magnetic force due to the motion of the rod. Explain. d. What is the retarding force on the rod when K is closed? e. How much power is required (by an external agent) to keep the rod moving at the same speed (=12cms^(-1)) when K is closed? How much power is required when K is open? f. How much power is dissipated as heat in the closed circuit? What is the source of this power? g. What is the induced emf in the moving rod if the magnetic field is parallel to the rails instead of being perpendicular?