Physics Test 276

Strong electromagnets are situated above the rails in some electrically powered trains.

When the electromagnets are activated, the eddy currents induced in the rails oppose the motion of the train.

When a changing magnetic flux is applied to a bulk piece of conducting material then circulating currents called eddy currents are induced in the material.

So, by the above explanation, we can understand that the generation of eddy current depends on the magnetic field but it is independent of the direction of the magnetic field.

Therefore, the eddy current will also generate when the north and the south poles are replaced with each other and that eddy currents induced in the rails oppose the motion of the train. So, the velocity of the train will decrease.

Given: Self-inductance of first coil (L₁) = 108 mH, Radius of both coils are same i.e., r₁ = r₂ = r, Number of turns of the first coil (N₁) = 200, and Number of turns of the second coil (N₂) = 500

Given:

Voltage across the Resistor R (V_R) = 80 V

Voltage across the Inductor L (V_L) = 40 V

Voltage across the Capacitor C (V_C) = 100 V

For a series LCR circuit, the total potential difference of the circuit is given by:

According to the second experiment of Faraday and Henry, we can say that when a current-carrying coil is moved towards or away from another coil then an emf gets induced in the coil.

If the circuit is closed in which the coil is connected then a current will also get induced in the coil. The relative motion between the two coils is required to induce a current in the coil.

In the given case when the primary coil is rotated about its axis there will be no relative motion between the primary and the secondary coil.

Since, there is no relative motion between the primary and the secondary coil so no current will induce in the primary coil.

The Lenz law states that the induced emf in a coil due to a changing magnetic flux is such that the magnetic field created by the induced emf opposes the change in a magnetic field.

When the north pole of a magnet is moved towards a coil that is connected to a circuit, the distance between the magnet and the coil will reduce, and magnetic flux associated with the coil is increased.

Due to this change in magnetic flux, an emf will induce in the coil and the direction of the induced emf will be such that it tries to stop the change of magnetic flux.

Therefore, the direction of current will be such that it stops the motion of the magnet and it is only possible when the north pole is formed on the magnet side of the coil so that the coil can repel the magnet.

We know that if the current in the coil is clockwise, the face of the coil towards the observer behaves as the south pole and if the current in the coil is anti-clockwise, the face of the coil towards the observer behaves as the north pole.

So, for the formation of the north pole on the magnet side, the current in the coil will be anti-clockwise when the coil is seen from the magnet side.

We know that if there are two solenoids of equal length and one solenoid is placed coaxially inside the other solenoid then the mutual inductance of solenoid 1 with respect to solenoid 2 will be equal to the mutual inductance of solenoid 2 with respect to solenoid 1.

The mutual inductance of both the solenoids is given as,

Where, n₁ = number of turns per unit length of solenoid 1, n₂ = number of turns per unit length of solenoid 2, r₁ = radius of the inner solenoid, and l = length of both the solenoids

By equation (1) it is clear that the mutual inductance of both the solenoids does not depend on the current in the solenoids.

Therefore, when the current in both the solenoids is doubled, the mutual inductance of both the solenoids S₁ and S₂ will remain unchanged.

Given: DC voltage EP = 120 V (Primary coil)

• The transformer works on the principle of mutual inductance.
• To induce emf in the secondary coil of the transformer, the magnetic flux associated with the secondary coil must change with respect to time.
• When the DC voltage is applied at the primary coil of the transformer, the magnetic flux associated with the coil will remain constant with respect to time. So the emf will not induce at the secondary coil.
• Therefore, when the DC voltage is applied at the primary coil, the induced emf in the secondary coil will be zero.

When the magnet oscillates in and out of the spring, it induces an EMF, the direction in which EMF is getting induced will be different.

Due to the induced EMF, a current will be set up in the coil which will deflect the pointer in the galvanometer in the opposite directions, as the magnet oscillates in and out of the spring an eddy current is set up in it decreases the amplitude of oscillation.

In short, the EMF will be induced in opposite directions, i.e., Left and Right, as the magnet oscillates in and out of the spring also the eddy current will reduce the amplitude of oscillation as the time goes on (Damping).

Radiowaves electromagnetic waves have the longest wavelength.

An electromagnetic wave is a wave radiated by an accelerated or oscillatory charge in which a varying magnetic field is the source of electric field and varying electric field is the source of magnetic field. In simple words we can say that the electromagnetic waves are composed of oscillating magnetic fields and electric fields. The abbreviation for electromagnetic waves is EM waves.

Charged particles—such as electrons and protons—create electromagnetic fields when they move, and these fields transport the type of energy we call electromagnetic radiation, or light.

There are basically seven types of electromagnetic waves which are a part of the electromagnetic spectrum. These are radio waves, microwaves, infrared waves, X-rays, gamma rays, ultraviolet waves and visible rays.

In all these seven electromagnetic waves, radio waves have the longest wavelength and the shortest frequency whereas gamma rays have the shortest wavelength and the shortest frequency.

So, the final answer is that the radio waves have the longest wavelength among all the electromagnetic waves.

Maxwell’s displacement current is a response to the inconsistency in Ampere’s law.

Maxwell showed that Ampere's circuital law is logically inconsistent. He considered a parallel plate capacitor being charged by a battery. He showed inconsistency of the law in the regions outside the plates of the capacitor and just between the plates. To resolve this inconsistency displacement current was introduced by Maxwell.