Class 10 Science Chapter 12 Magnetic Effects of Electric Current

Key Concept: Application of Law

b) It halves
[Solution Description] The magnetic field at the center of a circular loop is given by $B = \frac{\mu_0 I}{2R}$, where I is the current and R is the radius of the loop. By doubling the radius, the magnetic field strength becomes half its original value because B is inversely proportional to the radius.

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Key Concept: Current Reversal

a) The direction of the magnetic field lines reverses
[Solution Description] Upon reversing the current in a wire, the direction of the magnetic field lines also reverses. If the field was initially clockwise, it becomes counter-clockwise and vice versa.

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Key Concept: Field Line Patterns

b) Parallel straight lines inside, closed curves outside
[Solution Description] Iron filings align along the magnetic field lines. Around a solenoid, these lines are parallel inside and resemble those around a bar magnet outside—forming continuous loops from one end of the solenoid to the other.

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Key Concept: Compass Deflection

a) East
[Solution Description] According to the right-hand thumb rule, when the thumb points in the direction of current flow (north to south), fingers curl in the direction of magnetic field lines, which will result in the compass needle’s north pole deflecting towards the east.

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Key Concept: Current Direction Change

b) It reverses

[Solution Description] When the direction of the current in a straight wire is reversed, the direction of the magnetic field lines also reverses according to the right-hand thumb rule. This means the concentric circles describing the field shift their orientation accordingly.

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Key Concept: Solenoid Field

b) Uniform and strong
[Solution Description] Inside a long current-carrying solenoid, the magnetic field lines are parallel and uniformly distributed. This indicates that the magnetic field is uniform throughout the interior of the solenoid.

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Key Concept: Safety Measures

b) Using earth wire
[Solution Description] Using an earth wire is a safety measure in domestic circuits. It helps prevent electric shocks by providing a low-resistance path for the current, thereby ensuring user safety.

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Key Concept: Field Comparison

c) Both have similar field patterns with poles at ends.
[Solution Description] A solenoid produces a magnetic field similar to that of a bar magnet, with one end acting as a north pole and the other as a south pole. Inside the solenoid, the field lines are parallel and uniform, resembling the internal field lines of a bar magnet.

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Key Concept: Directional Change

b) It reverses
[Solution Description] Reversing the direction of the magnetic field results in the reversal of the direction of force on the current-carrying conductor, as given by Fleming’s Left-Hand Rule.

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Key Concept: Electric Motor Components

b) Commutator
[Solution Description] A commutator is a key component of an electric motor that reverses the direction of current flow, allowing for continuous rotation and thereby aiding in the conversion of electrical energy to mechanical energy.

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Key Concept: Magnetic Field Pattern

c) Concentric circles centered on the wire
[Solution Description] The magnetic field lines around a long straight current-carrying wire form concentric circles centered on the wire. This pattern emerges because the circular symmetry of the system dictates that at any point in space, the tangent to the magnetic field line is perpendicular to the radial direction from the wire.

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Key Concept: Circular Loop Field

d) They appear as straight lines perpendicular to the plane of the loop.
[Solution Description]
At the center of a current-carrying circular loop, the magnetic field lines are straight and perpendicular to the plane of the loop. This happens because every section of the wire contributes to the magnetic field lines in the same direction within the loop, and these contributions add up to appear as straight lines at the center.

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Key Concept: Field Strength

c) It decreases
[Solution Description] The magnetic field strength decreases as you move away from a current-carrying wire because the concentric circles representing the field become larger and more spaced apart.

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Key Concept: Magnetic Field Direction

a) Direction of force

[Solution Description] In Fleming’s left-hand rule, the thumb indicates the direction of the force experienced by a current-carrying conductor placed in a magnetic field.

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Key Concept: Direction Identification

d) North

[Solution Description]

Using the right-hand thumb rule, if you curl your fingers in the direction of the magnetic field while your thumb points upward (current direction), the magnetic field lines will circle counterclockwise. Therefore, at a point towards the east, the magnetic field direction will be north.

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Key Concept: Oersted’s Impact, Electromagnetic Induction

b) Fiber optics
[Solution Description] Hans Christian Oersted’s discovery that an electric current creates a magnetic field laid the foundation for understanding electromagnetism. This understanding is crucial for technologies that use electromagnetic waves for data transmission, such as radio, television, and fiber optics. Among these, fiber optics employs the principle of transmitting data through light, a form of electromagnetic wave, significantly influenced by Oersted’s findings.

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Key Concept: Real-world Application

a) Out of the page
[Solution Description] According to Fleming’s left-hand rule, if the magnetic field is downwards and the current flows clockwise, then each side of the coil experiences a different force. For the side of the coil facing you, the current is flowing to the right. By applying Fleming’s left-hand rule, with the forefinger pointing downwards (magnetic field), and the second finger pointing right (current), the thumb will point out of the page, indicating the direction of the force.

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Key Concept: Field Line Representation, Field Line Application

b) Constant within, then gradual decline extending outside.

[Solution Description] Inside a solenoid, the magnetic field is quite uniform and strong due to the aligned loops of current-carrying wire. However, as you move towards one end and beyond it, the magnetic field weakens and spreads out.

Graphically, the field strength inside will remain approximately constant. As we approach the edge, the field strength starts dropping gradually and continues to decrease further outside until negligible far away from the solenoid.

This curve resembles a plateau-like shape where it’s mostly level inside but slopes downward approaching and moving past the end.

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Key Concept: Current Rating

c) 15 A
[Solution Description] High-power appliances such as geysers are connected to a circuit with a higher current rating, typically 15 A, to handle the increased load without causing damage.

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Key Concept: Basic Safety

b) Using a fuse
[Solution Description] Using a fuse is a fundamental safety measure in domestic electric circuits. It protects against overcurrent situations like overloading and short-circuits by interrupting the power supply when necessary.

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Key Concept: Current Effect

c) It increases
[Solution Description] As the electric current in the wire increases, the magnetic field strength around the wire also increases, resulting in a greater deflection of the compass needle placed near it.

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Key Concept: Concept Application

c) Bringing the South pole of the bar magnet near the South pole of the solenoid will cause repulsion.
[Solution Description] When a solenoid is energized by a battery, it produces a magnetic field similar to a bar magnet. One end behaves like the North pole and the other like the South pole. Thus, if a permanent bar magnet is brought close to the solenoid, opposite poles will attract each other while like poles will repel.

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Key Concept: Field Line Direction

b) Anti-clockwise
[Solution Description] According to the right-hand thumb rule, if the thumb of the right hand is pointed in the direction of the current, then the direction in which the fingers curl around the conductor gives the direction of the magnetic field lines.

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Key Concept: Compass Needle

c) Towards the south pole
[Solution Description] A compass needle aligns itself with the external magnetic field. Hence, near the south pole of a bar magnet, the north pole of the compass needle points towards the south pole of the magnet due to the attraction between unlike poles.

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Key Concept: Right-Hand Thumb Rule

d) Surrounding the wire in concentric circles
[Solution Description] According to the right-hand thumb rule, if you hold a straight conductor carrying current in your right hand such that your thumb points in the direction of the current flow, then the fingers wrapped around the conductor show the direction of the magnetic field lines. Therefore, the direction of the magnetic field is represented by the curled fingers and will form concentric circles around the wire.

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Key Concept: Conceptual Understanding

d) Due to the magnetic field produced by the current
[Solution Description] A current-carrying conductor produces a magnetic field around it. When a compass needle, which itself acts as a small magnet, is placed in this external magnetic field, it experiences a torque that causes it to align with the resultant magnetic field, causing deflection.

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Key Concept: Energy Source

b) Mechanical to electrical
[Solution Description]
A generator converts mechanical energy into electrical energy based on electromagnetic induction principles.

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Key Concept: Magnetic Interaction

c) The field lines reverse their direction
[Solution Description] When the current through a straight conductor is reversed, the direction of the magnetic field lines around the conductor also reverses. This can be observed by using a compass near the wire; the needle will deflect in the opposite direction when the current’s direction is changed.

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