NEET Mock Test - 30 - NEET MCQ

At t = 0, inductor in replaced by an open circuit. 

Since electron is moving along the field, force qE is repulsive and hence it will slow down. 

Construct an Ampere’s loop in the concerned regions to see the value of i_p.

At a pont outside the co-axial tube at a diatance R from the central axis consider a circular path.
Then from Amperes Law closed integral of B.dl=μ₀I(net)
the net current is zero as the current in the two cables flow in opposite directions.

therefore Magnetic field is zero outside

Velocity v acquired  by the electron and accelerating  potential V are related by,
where e and m are charge and mass of the electron

Radius of the circular track:

The radius r of the path of charged particle with charge q in a uniform magnetic field(B) is given by

Now, if charge of singly ionized ion is e, then charge of doubly ionized ion is 2e. Hence, the circle described by the singly ionized charge will have a radius double that of the other one. 

Work done by electric field = Change in K.E. 

Using lenz law, it is evident that the induced current in the ring will oppose the effect caused by the current in the larger loop. When current is flowing in the larger loop a magnetic field will be set and the ring will oppose it, thus, inducing current in clockwise direction. Similarly when the switch is turned off, the induced current will be in anti-clockwise direction.

Due to electromagnetic induction, emf e is induced across the ends of the rod. This induced emf is given by
e=Bvl
The direction of this induced emf is from A to B, that is, A is at the higher potential and B is at the lower potential. This is because the magnetic field exerts a force equal to qvB on each free electron where q is −-1.6 × 10^-16 C. The force is towards AB by Fleming's left-hand rule; hence, negatively charged electrons move towards the end B and get accumulated near it. So, a negative charge appears at B and a positive charge appears at A.

Assume current i passes  through outer loop. Then  and 

No power loss in case of an ideal transformer. 

Maximum power is transferred at resonance. 

or 

IR because temperature of the body is 37°C and it emits heat radiation which falls in IR and microwave region.

At room temperature permanent magnet behaves as a ferromagnetic substance for a long period of time. At room temperature, the permanent magnet retains ferromagnetic property for a long period of time.

The individual atoms in a ferromagnetic material possess a dipole moment as in a paramagnetic material.

However, they interact with one another in such a way that they spontaneously align themselves in a common direction over a macroscopic volume called domain. Thus, we can say that in a permanent magnet at room temperature, domains are all perfectly aligned.

Key concept: The electrostatic field lines, do not form a continuous closed path (this follows from the conservative nature of electric field) while the magnetic field lines form the closed paths.

Which implies that number of magnetic field lines entering the Gaussian surface is equal to the number of magnetic field lines leaving it. Therefore case (ii) is not possible.

Key concept: The self inductance L of a solenoid depends on various factor like geometry and magnetic permeability of the core material.
L = μ_r μ₀ n² Al
where, n = N/l (no. of turns per unit length)
1.   No. of turns: Larger the number of turns in solenoid, larger is its self inductance.
2.  Area of cross section: Larger the area of cross section of the solenoid, larger is its self inductance.
3.  Permeability of the core material. The self inductance of a solenoid increases μr times if it is wound over an iron core of relative permeability μr.
The long solenoid of cross-sectional area A and length l, having A turns, filled inside of the solenoid with a material of relative permeability (e.g., soft iron, which has a high value of relative permeability) then its self inductance is L = μ_rμ₀ N² A/l
So, the self inductance L of a solenoid increases as l decreases and A increases because L is directly proportional to area and inversely proportional to length.
Important point: The self and mutual inductance of capacitance and resistance depend on the geometry of the devices as well as permittivity/ permeability of the medium.  

Key concept: As we know whenever the number of magnetic lines of force (magnetic flux) passing through a circuit changes an emf is produced in the circuit called induced emf. The induced emf persists only as long as there is a change or cutting of flux.
The induced emf is given by rate of change of magnetic flux linked with the circuit, i.e., e = -dФ/dt
According to the problem there is no electromotive force produced in the coil. Then the various arrangement are to be thought of in such a way that the magnetic flux linked with the coil does not change even if the coil is placed and expanded in magnetic field.
When circular coil expands radially in a region of magnetic field such that the magnetic field is in the same plane as the circular coil or we can say that direction of magnetic field is perpendicular to the direction of area (increasing) so that their dot product is always zero and hence change in magnetic flux is also zero.

Or
The magnetic field has a perpendicular (to the plane of the coil) component whose-magnitude is decreasing suitably in such a way that the dot product of magnetic field and surface area of plane of coil remain constant at every instant.