Emi Flashcards
Two spherical bobs, one metallic and the other of glass, of the same size are allowed to fall freely from the same height above the ground. Which of the two would reach earlier and why?
Glass would reach earlier. This is because there is no effect of electromagnetic induction in glass, due to presence of earth’s magnetic field, unlike in the case of metallic ball.
A long straight current carrying wire passes normally through the centre of circular loop. If the current through the wire increases, will there be an induced emf in the loop? Justify.
No.
Justification: As the magnetic field due to current carrying wire will be in the plane of the circular loop, so magnetic flux will remain zero. Also, magnetic flux does not change with the change in current.
On what factors does the magnitude of the emf induced in the circuit due to magnetic flux depend?
It depends on the rate of change in magnetic flux (or simply change in magnetic flux).
A conducting rod of length is kept parallel to a uniform magnetic field B. It is moved along the magnetic field with a velocity i. What is the value of emf induced in the conductor.
Conducting rod of length L is kept parallel to a uniform, magnetic field B and moved along it with velocity V. The value of EMF induced equal to zero.
A wire in the form of a tightly wound solenoid is connected to a DC source, and carries a current. If the coil is stretched so that there are gaps between successive elements of the spiral coil, will the current increase or decrease? Explain.
The current will increase. As the wires are pulled apart the flux will leak through the gaps. Lenz’s law demands that induced emf resist this decrease, which can be done by an increase in current.
A solenoid is connected to a battery so that a steady current flows through it. If an iron core is inserted into the solenoid, will the current increase or decrease? Explain.
The current will decrease. As the iron core is inserted in the solenoid, the magnetic field increases and the flux increases. Lenz’s law implies that induced emf should resist this increase, which can be achieved by a decrease in current. However, this change will be momentarily.
Electromagnetic Induction
The phenomenon of generation of induced emf and induced current due to change in magnetic field lines associated with a closed circuit is called electromagnetic induction.
Faraday’s Laws of Electromagnetic Induction
(i) Whenever there is a change in magnetic flux linked with a coil, an emf is induced in the coil.
The induced emf is proportional to the rate of change of magnetic flux linked with the coil.
(ii) emf induced in the coil opposes the change in flux,
Lenz’s Law
The polarity of induced emf is such that it tends to produce a current
which opposes the change in magnetic flux that produced it.
EMF Induced in a Moving Conducting Rod
field of induction B, such that B, I and v are mutually perpendicular, is given by
E=Blv
force required to keep the rod in constant motion is F = BIL
Self induction
When the current in a coil is changed, an induced emf is produced in the same coil. This phenomenon is called self-induction.
Mutual induction
When two coils are placed nearby and the current in one coil (often called primary coil) is changed, the magnetic flux linked with the neighbouring coil (often called secondary coil) changes; due to which an emf is induced in the neighbouring coil. This effect is called the mutual induction.
Mutual induction
When two coils are placed nearby and the current in one coil (often called primary coil) is changed, the magnetic flux linked with the neighbouring coil (often called secondary coil) changes; due to which an emf is induced in the neighbouring coil. This effect is called the mutual induction.
Mutual inductance
The mutual inductance of two coils is defined as the magnetic flux linked with the secondary coil when the current in primary coil is 1 ampere.
