Test: Magnetic Effects of Electric Current - 1 - UPSC MCQ

An electric fuse prevents damage to the appliances and circuits due to short-circuiting, which can occur when the live wire and the neutral wire come into direct contact, causing an abrupt increase in current flow.

In the context of magnetic fields, a solenoid is defined as a coil of many circular turns of insulated wire. Solenoids are crucial components in electromagnets and various electrical devices due to their ability to generate strong and uniform magnetic fields.

• The Assertion is correct. Magnetic field lines always form closed loops around a current-carrying conductor.
• The Reason is also correct as magnetic monopoles, isolated magnetic charges (separate north or south poles), have not been observed in nature.
• However, the Reason does not provide a direct explanation for the Assertion. The formation of closed loops in magnetic fields is a consequence of the fundamental property of magnetic fields, not directly related to the absence of magnetic monopoles.
• Therefore, the correct option is revealed through detailed examination.

Hans Christian Oersted accidentally discovered the deflection of a compass needle near a metallic wire when an electric current passed through it, revealing the relationship between electricity and magnetism.

• The earth wire in a domestic electric circuit is primarily installed to protect against electric shocks. It provides a low-resistance path for the current, ensuring that any leakage of current to the metallic body of an appliance keeps its potential equal to that of the earth.
• This safety measure prevents users from experiencing severe electric shocks.

An electric motor converts electrical energy into mechanical energy.

• The Assertion is correct. When a metallic wire carries an electric current, it generates a magnetic field around it. This phenomenon is a fundamental aspect of electromagnetism.
• The Reason is also correct. The magnetic field around the wire indeed forms concentric circles, and the direction of these circles is determined by the right-hand rule.
• However, the Reason statement is not the correct explanation of the Assertion. While both statements are individually true, the Reason does not directly explain why a metallic wire carrying an electric current produces a magnetic field.

• Assertion (A) is true; magnetic field lines around a bar magnet are indeed closed curves.
• Reason (R) is also true; inside the magnet, the direction of field lines runs from its south pole to its north pole.
• However, the Reason does not correctly explain Assertion, as the closure of field lines is a consequence of the overall magnetic field configuration rather than just the direction of the field lines inside the magnet.

• Option A is correctly matched. The right-hand thumb rule is used to determine the direction of the magnetic field around a current-carrying straight conductor. According to this rule, if you hold the conductor in your right hand such that your thumb points in the direction of the current, your fingers will curl around the conductor in the direction of the magnetic field lines.
• Option B is incorrect. The right-hand thumb rule specifically applies to a straight conductor, not a circular loop. For a current-carrying circular loop, the magnetic field lines form concentric circles at every point of the loop and appear as straight lines at the center.
• Option C is incorrect. Maxwell's corkscrew rule is another way of describing the right-hand thumb rule for determining the direction of the magnetic field around a current-carrying conductor. It does not describe the motion of charged particles in a magnetic field.
• Option D is incorrect. Magnetic field lines never intersect each other. If they did, it would imply that there are two different directions of the magnetic field at the point of intersection, which is not possible.

A compass needle is affected by magnetic fields. When it is brought near a bar magnet, the magnetic field of the bar magnet causes the needle to deflect. A plastic rod does not produce a magnetic field, so it will not affect the compass needle.

The magnetic field is stronger where the field lines are closer together, indicating a higher concentration of magnetic force in that region. This closeness of field lines signifies a greater force acting on the poles of another magnet placed in that area.

Electromagnetic induction is the phenomenon due to which an induced current is set up in a coil when magnetic field around it, is changed.

In Fleming’s left-hand rule the thumb indicates the direction of mechanical force acting on the conductor. The forefinger points in the direction of magnetic field and the central finger in the direction of current flowing in the conductor.

When a proton moves freely in a magnetic field, its velocity can change. This change occurs due to the interaction between the magnetic field and the moving charge, leading to alterations in the proton's direction and speed.

• The Assertion is true as per the information provided in the text. As the distance from a current-carrying conductor increases, the deflection of a compass needle does indeed decrease.
• The Reason is true. The magnetic field produced by a given current in the conductor decreases as the distance from it increases, as explained in the content.
• However, the Reason is not the correct explanation of the Assertion. While both statements are individually correct, the decrease in deflection with distance is due to the weakening magnetic field, not necessarily because the magnetic field decreases in magnitude. Hence, Option C is the correct answer for this question.

A metallic wire carrying an electric current generates a magnetic field around it. This phenomenon is a fundamental concept in electromagnetism, demonstrated by the right-hand rule.

Fuse wire must have high conductivity, low melting point and it do not burn due to oxidation. These characteristics of a fuse wire make it possible to prevent from damages.

AC transmit over a long distance without much loss of energy as compare to DC.

Overloading occurs when there is any fault in the appliances or the insulation of wire got damaged. It also occurs when there is sudden hike in supply voltage.

• The correct answer is the Right-hand thumb rule, which helps in determining the direction of magnetic field lines around a current-carrying straight conductor.
• When the thumb points in the direction of the current, the fingers wrap around the conductor in the direction of the magnetic field lines.

• Option A: Electric generator - Converts mechanical energy to electrical energy. This is correct because an electric generator functions by converting mechanical energy into electrical energy through electromagnetic induction.
• Option B: Electric motor - Converts electrical energy to sound energy. This is incorrect. An electric motor converts electrical energy to mechanical energy, not sound energy.
• Option C: Loudspeaker - Converts electrical energy to mechanical energy. This is incorrect. A loudspeaker converts electrical signals (electrical energy) into sound energy (mechanical vibrations of the diaphragm).
• Option D: Microphone - Converts magnetic energy to electrical energy. This is incorrect. A microphone converts sound energy (mechanical energy) into electrical energy.

Thus, the correct match is provided in Option A.

• The assertion is correct. When a circular loop of wire lies in the plane of the table with current passing through it clockwise, the right-hand rule helps determine the direction of the magnetic field inside and outside the loop. This rule states that if the thumb points in the direction of the current, the fingers curl in the direction of the magnetic field lines.
• Regarding the reason, it is also correct. A uniform magnetic field means that the field strength and direction are consistent throughout the region in question.
• However, the reason does not directly explain the assertion. While a uniform magnetic field is mentioned in the reason, it does not serve as a direct explanation for how the right-hand rule is used to determine the magnetic field direction around a current-carrying loop.
• Therefore, the correct answer is Option B: If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

• A fuse in an electrical circuit serves the crucial role of safeguarding the circuit from short-circuiting or overloading. It does so by breaking the circuit when excessive current flows through it, thereby preventing damage to the components and ensuring safety.
• Fuses are designed to melt and interrupt the flow of current when the current exceeds a safe level, thus protecting the circuit from potential hazards.

The pattern of the magnetic field generated by a current through a conductor is primarily determined by the shape of the conductor. Different shapes of conductors can produce varied patterns of magnetic fields based on their geometries and orientations.

• Option A: Live wire - Green insulation:
  • This is incorrect. According to the provided content, the live wire has red insulation, not green. The green insulation is used for the earth wire.
• Option B: North pole - Points towards north:
  • This is correct. The content states that one end of a compass needle, which points towards the north, is called the north pole.
• Option C: Magnetic field lines - Straight lines:
  • This is incorrect. The content describes magnetic field lines as paths along which a hypothetical free north pole would tend to move, and they are shown closer together where the magnetic field is greater. They are not necessarily straight lines.
• Option D: Neutral wire - Red insulation:
  • This is incorrect. According to the content, the neutral wire has black insulation, not red. The red insulation is for the live wire. Therefore, the correctly matched pair is Option B: North pole - Points towards north.

A "grounding" wire on the other hand is a safety wire that has intentionally been connected to earth. The grounding wire does not carry electricity under normal circuit operations. It's purpose is to carry electrical current only under short circuit or other conditions that would be potentially dangerous.

The concentric circles around a straight conducting wire represent the magnetic field lines produced by the electric current flowing through the wire. These lines indicate the direction and strength of the magnetic field surrounding the wire.

An electric fuse plays a crucial role in preventing damage to appliances and circuits caused by overloading. When there is an abrupt increase in current due to short-circuiting or other faults, the fuse melts to break the circuit, safeguarding the system from potential harm.

• Option A: (a) Hans Christian Oersted - Discovered the magnetic effect of electric current in 1820 This is the correct pair. Hans Christian Oersted, in 1820, discovered that a compass needle gets deflected when an electric current passes through a nearby metallic wire, demonstrating the magnetic effect of electric current.
• Option B: (b) Compass needle - Always points towards the west This is incorrect. A compass needle points towards the north and south directions, not the west.
• Option C: (c) Iron filings - Represent electric field lines This is incorrect. Iron filings align along magnetic field lines, not electric field lines.
• Option D: (d) North pole - Repels the south pole of another magnet This is incorrect. The north pole of a magnet attracts the south pole of another magnet, while like poles repel each other.

Fleming’s right-hand rule gives the direction of induced current in a rectangular coil when the coil is rotated in a uniform magnetic field.