Test: Magnetic Effects of Electric Current - 2 - UPSC MCQ

The region around a magnet, in which its influence can be felt, is called its magnetic field

Let a constant current I flows through a horizontal wire from east to west. The direction of magnetic field, as per right-hand thumb rule, will be from north to south at a point directly below the current-carrying wire.

The direction of magnetic field developed around a current-carrying conductor can be found by the use of right-hand thumb rule.

The strength of the magnetic field around a current-carrying straight conductor is directly proportional to the amount of current flowing in the conductor.

The correct answer is: a) soft iron

The core of an electromagnet should be made of soft iron because it has the following properties that are ideal for an electromagnet:

1. High Magnetic Permeability: Soft iron can easily become magnetized when an electric current flows through the surrounding coil.
2. Low Retentivity: It loses its magnetism quickly when the current is stopped, which is essential for the electromagnet to be effective and controllable.
3. Efficient Magnetic Induction: Soft iron enhances the strength of the magnetic field generated by the coil.

Other options are not suitable:

• Hard iron: Retains magnetism and is not ideal for an electromagnet, as it does not allow for quick switching of the magnetic field.
• Rusted iron: Poor conductor of magnetic flux and inefficient for creating a strong magnetic field.
• None of the above: Incorrect, as soft iron is the best choice.

The strength of a magnetic field inside a long, current-carrying, straight solenoid is uniform at all points. Moreover, the field depends on the amount of current flowing and the number of turns in solenoid coil besides its length

It is most important method for protecting the electrical devices from short circuiting or overloading by stopping the flow of any large electric current exceeds from its rating.

A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. This is essential in many electronic devices that require a stable DC power supply.

The strength of magnetic field along the axis of a solenoid coil increases on increasing the current flowing through the solenoid coil and on increasing the number of turns in the solenoid coil. Moreover, if a soft iron core is inserted inside the solenoid coil then magnetic field increases many fold.

A current carrying solenoid produces a uniform magnetic field inside it.

When a current-carrying straight conductor is placed perpendicular to the direction of a uniform magnetic field, it experiences a mechanical force. The direction of mechanical force is given by Fleming’s left-hand rule.

Using electromagnet, the magnetic field strength further increase by increasing the current. Hence it will enhance the power of electric.

On applying Fleming’s left-hand rule we find that both electron as well as proton experience forces pointing into the plane of paper.

A solenoid behaves like a bar magnet. Hence the pattern of magnetic field associated with solenoid and around the bar magnet is same.

Like magnetic poles (say N- and N-poles) always repel each other.

- When a circuit carrying current is closed, it generates a magnetic field around it.
- According to Ampère's circuital law and the right-hand rule, the magnetic field lines around a straight current-carrying conductor form concentric circles.
- These circles are centered on the wire, and their planes are perpendicular to the direction of the current.
- Therefore, on a horizontal plane like ABCD, the magnetic field lines appear as concentric circles, making option A correct.

The correct answer is: C) Increase in the number of turns in the coil

To increase the strength of the magnetic field produced by a coil, the following changes could help:

• Increasing the number of turns in the coil: This directly increases the magnetic field strength. More turns mean that for a given current, the magnetic effect is stronger.

Decreasing the number of turns or replacing the coil would not enhance the magnetism. Therefore, option C is the correct change the boy likely made.