Comparing Solenoid and Bar Magnet

Introduction:
Solenoid and bar magnet are two types of magnets that have different properties. However, there are some similarities between them. In this question, we need to identify the case where there is no exact similarity between solenoid and bar magnet.

Answer:
The correct answer is option 'A' - "There is a current entering and a current leaving a solenoid". Let's understand why this is the correct answer.

Solenoid:
A solenoid is a coil of wire that produces a magnetic field when an electric current is passed through it. The magnetic field produced by a solenoid is similar to that of a bar magnet. However, there are some differences.

Bar Magnet:
A bar magnet is a permanent magnet that has a north pole and a south pole. The magnetic field of a bar magnet is uniform and is strongest at the poles.

Comparison:
Now let's compare the two magnets based on the given options.

a) There is a current entering and a current leaving a solenoid:
This is a property unique to solenoids. When an electric current is passed through a solenoid, there is a current entering at one end and a current leaving at the other end. This is because a solenoid is a coil of wire that is wrapped around a core. As a result, the magnetic field produced by a solenoid is concentrated inside the coil and is weaker outside.

b) Solenoid can be broken into two weaker solenoids:
This is a property that is similar to a bar magnet. A bar magnet can be broken into two weaker magnets, each with its own north and south pole. Similarly, a solenoid can be broken into two weaker solenoids, each with its own magnetic field.

c) Flux lines enter one end of a solenoid:
This is a property that is similar to a bar magnet. The magnetic field of a bar magnet is uniform and the flux lines enter at one end and exit at the other end. Similarly, the magnetic field of a solenoid is strongest at the ends and the flux lines enter at one end and exit at the other end.

d) Moving a small compass needle in the neighbourhood of a solenoid enables tracing the flux lines:
This is a property that is similar to a bar magnet. The magnetic field of a bar magnet can be visualized using iron filings or a small compass needle. Similarly, the magnetic field of a solenoid can be visualized using a small compass needle.

Conclusion:
Based on the above comparison, we can see that option 'A' is the correct answer as it is the only option that is unique to solenoids and does not have a similar property in bar magnets.