The question asks about the existence of magnetic monopoles. This is a fundamental concept in electromagnetism and physics. The key is to recall the current understanding and experimental evidence regarding magnetic monopoles.
C) Magnetic monopole does not exist — This statement aligns with current scientific understanding and experimental observations. While theoretically proposed in some advanced theories, they have not been found.
The question asks to identify the instrument used to measure magnetic flux. We need to recall the primary function of each given instrument.
D) Magnetometer — A magnetometer is an instrument that measures magnetic fields. Since magnetic flux is derived from the magnetic field strength over an area, a magnetometer is the appropriate instrument for measuring or determining magnetic flux.
The question asks about the type of magnet a bar magnet represents. We need to understand the fundamental characteristics of different types of magnets to identify the correct option.
Correct Option: A) A bar magnet is a classic example of a permanent magnet because it retains its magnetic properties without the need for an external electric current or field.
The question asks to identify the point in a bar magnet where the magnetic force is zero. This relates to understanding the distribution of magnetic field lines and the strength of the magnetic field within and around a bar magnet.
Correct Option: C) At the center
The magnetic field lines are densest at the poles and spread out as they move towards the center. At the geometric center of the bar magnet, the magnetic field strength is minimal, and ideally zero, due to the opposing effects of the two poles. Consequently, the magnetic force is zero at the center.
The question asks to identify the device formed when a soft iron core is placed inside a solenoid. This involves understanding the basic principles of magnetism and electromagnetic induction.
Correct Option: B) An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. The magnetic field disappears when the current is turned off. Using a soft iron core inside a solenoid significantly enhances the magnetic field and makes it a powerful electromagnet.
To determine how to increase the magnetic field inside a solenoid, we need to recall the formula for the magnetic field produced by an ideal solenoid. This formula directly relates the magnetic field strength to physical properties of the solenoid and the current flowing through it.
C) Increasing the number of turns per unit length: As per the formula \(B = \mu_0 n I\), increasing \(n\) (number of turns per unit length) directly increases the magnetic field strength \(B\). This is because more turns packed into the same length contribute more to the magnetic field.