Test: Magnetism - EmSAT Achieve MCQ

• A solenoid is a coil of wire that produces a magnetic field when an electric current passes through it.
• A soft iron core is a magnetic material that can increase the strength of the magnetic field produced by a solenoid.
• Solenoid types include the following:
  • Rotary Solenoid.
  • Linear Solenoid.
  • AC-Laminated Solenoid.
  • DC-C Frame Solenoid.
  • DC-D Frame Solenoid.

• Plastic is not attracted to a magnet. Most plastics are non-magnetic.
• Carbon itself is not attracted to a magnet.
  • However, some forms of carbon, such as iron-carbon alloys (e.g., steel), can be magnetic.
• Aluminum is not attracted to a magnet. It is a non-magnetic substance.
• Stainless steel is generally not attracted to a magnet.
  • However, it may contain varying amounts of iron (iron-based) content, which may affect its magnetic properties.

• In Fleming's left rule, the middle finger represents the direction of current flowing through the conductor. So option 3 is correct.
• The thumb represents the direction of the magnetic force.
• The forefinger represents the direction of the magnetic field.

Fleming's Right-Hand Rule:

• Thumb: It is along the direction of motion of the conductor.
• Middle Finger: Indicates the direction of the induced current.
• Index Finger(forefinger):  Indicates the direction of the magnetic field.

Image: Fleming's Right-Hand Rule

Fleming's Left-Hand Rule:

• Thumb: It points towards the direction of motion (force)
• Middle Finger: It represents the direction of the induced current
• Index Finger:  It represents the direction of the magnetic field.

From the above explanation, we can see that

• Air is an example of paramagnetic material since under an external magnetic field it forms an electric dipole.

The Dynamo effect:

• It is a theory that explains the origin of the Earth's main magnetism in terms of a self-sustaining dynamo.
• In this dynamo mechanism, fluid motion in the Earth's outer core moves conducting material (liquid iron) across an already existing, weak magnetic field and generates an electric current.
• The electric current, in turn, produces a magnetic field that also interacts with the fluid motion to create a secondary magnetic field.
• Together, the two fields are stronger than the original and lie essentially along the axis of the Earth's rotation.

The Doppler Effect:

• The Doppler effect is the change in frequency of a wave with respect to an observer who is moving relative to the wave source.
• The changing pitch of the train siren is the best example of the Doppler effect.

The Magnus effect:

• The Magnus effect is related to the spinning bodies (either cylinder or sphere)
• When a soccer player kicks a ball off-centre it causes the ball to spin due to the Magnus effect.

Magnetism maxima and minima for a bar magnet

• Magnetism is strongest at the north poles and south poles of the magnet and weakest at the centre of a bar magnet.
• This is because the magnetic field lines run parallel to the length of the magnet at the centre and run closer and denser at the poles.
  • or it can be thought of as magnetic field lines are originated from a pole and not at the centre of the bar.

A natural magnet is an ore of Iron oxide(Fe₃O₄).

• A natural magnet is a magnet which occurs naturally in nature.
• All-natural magnets are permanent magnets, which means they can never lose their magnetic strength.
• Strong magnets can be found in sandy soils in various parts of the world.
• Lodestone, also called magnetite, is the best natural magnet substance.
• The stone is black in colour and very smooth when polished.
• The lodestone was originally used in the very first compass ever made.

• The solenoid is a long coil containing a large number of close turns of insulated copper wire.
• When electricity is passed through the solenoid, it acts as an electro magnet.
• The magnetic field produced by a current-carrying solenoid is similar to the magnetic field produced by a bar magnet.
• The magnetic field lines inside the solenoid are in the form of parallel straight lines.

• Soft iron defined as the iron that can easily be magnetized and demagnetized with a small quantity of hysteresis loss and has a low carbon content.
• It is used because it does not retain its magnetism power when the current is switched off. 
• In other words, we can understand that it does not become Permanently Magnetized.
• Soft Iron has low coercive force or low coercivity and low retentivity.
• The susceptibility of this iron is very high and very less corrosive.