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प्रश्न
State Lenz's Law.
उत्तर १
Lenz’s law: It is stated that the direction of induced e.m.f. is always in such direction that it opposes the change in magnetic flux.
`e=(d φ)/(dt)`
Consider a rectangular metal coil PQRS. Let ‘L’ be the length of the coil. It is placed in a partly magnetic field ‘B’. the direction of magnetic field is perpendicular to paper and into the paper. The ‘x’ part of the coil is in magnetic field at instant t. If the coil is moved towards right with a velocity v = dx/dt with help of external agent like hand. The magnetic flux through the coil is Φ= BA = BLx ∴Φ = B Lx -----(1) There is relative motion of a current through the coil. Let ‘i’ be current through the coil.
Three forces acts on the coil .
F1 on conductor PL ∴ F1 = Bix , vertically upward.
F2 on conductor MS ∴ F2 = Bix, vertically downward.
F3 on conductor SP ∴ F3 = BiL towards left.
F1 & F2 are equal and opposite and also in a same lines. They will cancel each other, F3 is a resultant force. The external agent has to do work against this force.
∴ F3 = - Bil -ve sign indicates that force is opposite to dx.
If dx is displacement in time dt, then work done dw = F3 dx
∴ dw = - BiL dx
This power is an electrical energy ‘ei’ where ‘e’ is an induced e.m.f.
`therefore ei=-(Bildx)/(dt)`
`therefore e=-(BLdx)/(dt)`
`therefore e= -BLv`
`therefore e=-d/dt (BLx)`
`therefore=e=-(d φ)/(dt)` from eq (1)
उत्तर २
The Lenz’s law states that the direction of induced current is such that it opposes the cause which produces it.
APPEARS IN
संबंधित प्रश्न
State Faraday's laws of electromagnetic induction.
In the following diagram an arrow shows the motion of the coil towards the bar magnet.
(1) State in which direction the current flows, A to B or B to A?
(2) Name the law used to come to the conclusion.
- How would you demonstrate that a momentary current can be obtained by the suitable use of a magnet, a coil of wire and a galvanometer?
- What is the source of energy associated with the current obtained in part (a)?
- Describe briefly one way producing an induced e.m.f?
- State one factor that determines the magnitude of induced e.m.f. in part (a) above.
- What factor determines the direction of induced e.m.f. in part (a) above?
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A conductor in the form of a circular arc of the radius of curvature R subtends an angle Ø at its centre of curvature. If the current in the conduct is I, the magnetic induction at the centre of curvature is ______.
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Name the principle of AC generator.
State the use of the principle of electromagnetic induction.
State two factors on which the magnitude of induced e.m.f. in a coil depend.
