CG Board Class 10 Science Chapter 12 Solutions: Magnetic Effects of Electric Current (विद्युत के चुम्बकीय प्रभाव) (2026-27)

(i) The magnetic lines of force determine:**

• (a) shape of the magnetic field
• (b) direction of the field
• (c) intensity of the magnetic field
• (d) intensity and direction of magnetic field

(b) direction of the field; in physical terms, lines of force convey both field intensity and direction, but as per CGBSE textbook Key: (b)).*

Explanation: The tangent drawn to a magnetic line of force at any point gives the direction of the magnetic field at that point.

Answer: (c) lines of force in concentric circles around the conductor

Explanation: Concentric circular field lines form in planes perpendicular to a straight current-carrying wire.

Answer: (b) same at each point

Explanation: Inside a long current-carrying solenoid, magnetic field lines are parallel straight lines, showing that the magnetic field is uniform (same) at all internal points.

Answer: (d) to produce induced current when either coil or magnet moves

Explanation: Electromagnetic induction is the process of generating an induced current in a circuit due to relative motion between a magnet and a coil.

Answer: (a) Generator

Explanation: An electric generator (dynamo) converts mechanical energy into electrical current.

(i) That device which converts mechanical energy into electrical energy is ……………………**

(ii) ……………………… converts electrical energy into mechanical energy.

(iii) Fleming’s left hand rule indicates the direction of ………………………

(iv) Fleming’s right hand rule indicates the direction of ……………………… acting on the conductor.

(v) Maxwell’s right hand / corkscrew rule indicates the direction of ………………………

• (i) Electric Generator (Generator / Dynamo)
• (ii) Electric Motor
• (iii) Force on current carrying conductor / Motion of conductor (Note: CGBSE textbook key lists “Induced current” for item iii and “Moving force” for item iv due to inverted numbering alignment in official table key; physically, Left Hand Rule gives Force/Motion and Right Hand Rule gives Induced Current)
• (iv) Induced current / Moving force
• (v) Magnetic lines of force / Magnetic field

Michael Faraday** discovered and gave the principle of electromagnetic induction in 1831.

Danish scientist Hans Christian Oersted (H.C. Orsted) first observed and confirmed the magnetic effect of electric current in 1810 / 1820.

1. Electric Fans
2. Washing Machines
3. Water Pumping Sets

(Other examples: Refrigerators, Mixer-Grinders, Electric Drills).

Fleming’s Right-Hand Rule:** Stretch the thumb, forefinger (first finger), and middle finger of your right hand mutually perpendicular to each other

• Forefinger: Points in the direction of the Magnetic Field.
• Thumb: Points in the direction of Motion of the conductor.
• Middle Finger: Points in the direction of the Induced Electric Current.

1. By a Permanent Bar Magnet: Using permanent natural or artificial bar magnets.
2. By a Straight / Circular Current-Carrying Conductor: Flowing electric current through a copper wire loop or straight conductor.
3. By a Solenoid / Electromagnet: Passing electric current through a coil wound around a soft iron core (Solenoid/Electromagnet).

Action as Magnet:** A solenoid is a cylindrical coil of tight insulated copper turns. When electric current flows through it, magnetic field lines emerge from one end and enter the other end, running parallel inside, exactly like the magnetic field of a bar magnet. Thus, one end acts as the North Pole and the other as the South Pole.

• Determining Poles using Bar Magnet:
• Suspend the current-carrying solenoid or bring a known bar magnet near its ends.
• Bring the North Pole of a bar magnet near one end of the solenoid
• If it is repelled, that end of the solenoid is the North Pole.
• If it is attracted, that end of the solenoid is the South Pole.

1. Attractive Property: Attracts magnetic substances like iron, steel, and nickel.
2. Directive Property: Freely suspended magnet always aligns itself along the geographic North-South direction.
3. Pairing of Poles: Magnetic poles always exist in pairs (N and S); isolated monopoles cannot exist.

Definition:** Imaginary continuous lines drawn in a magnetic field along which an isolated unit North Pole would move.

• Three Main Properties:

1. Continuous closed loops from N to S outside the magnet and S to N inside.
2. Two lines of force never cross/intersect each other.
3. Concentrated near poles (strong field) and dispersed away from poles (weak field).

If two magnetic lines of force were to intersect at a point, two tangents could be drawn at that single point of intersection. This would mean that a compass needle placed at that point would point in two different directions simultaneously, which is physically impossible.

(a) Labelled Diagram Description:**

• Rectangular copper coil ABCD (armature) placed between curved N-S poles of a magnet.
• Commutator split-rings X, Y connected to ends of coil.
• Stationary carbon brushes P, Q touching split rings and connected to battery and key.
• (b) Working Principle:

When electric current passes through a rectangular coil placed perpendicular to a magnetic field, equal and opposite forces act on its parallel arms (AB and CD), forming a torque that rotates the coil continuously.

• (c) Working Process:

1. When current enters arm AB from A → B and leaves CD from C → D, applying Fleming’s Left-Hand Rule causes a downward force on AB and an upward force on CD, rotating the coil anti-clockwise.
2. After half a rotation, split-rings X and Y swap contact brushes (P and Q), reversing the current direction in arms (DC → BA).
3. The force directions swap accordingly, allowing the coil to keep rotating continuously in the same anti-clockwise direction.

(a) Labelled Diagram Description:**

• Armature coil ABCD wound over soft iron core between strong magnetic poles N-S.
• Slip rings / Split rings R₁, R₂ mounted on rotating axis.
• Carbon brushes B₁, B₂ linked to load / galvanometer G.
• (b) Working Principle:

Based on Electromagnetic Induction. Rotating the armature coil in a magnetic field changes the magnetic flux passing through it, inducing an electric current according to Fleming’s Right-Hand Rule.

• (c) Working Process:

1. As axle rotates arm AB upwards and CD downwards in the magnetic field (N → S), induced current flows in direction A → B → C → D.
2. Current flows in external circuit from Brush B₁ → B₂.
3. After half rotation, CD moves upwards and AB downwards. Induced current direction in coil reverses to D → C → B → A.
4. In an AC generator (using full slip rings), external current reverses direction every half-cycle (Alternating Current). In a DC generator (using split rings), commutator maintains current direction from B₁ → B₂ continuously (Direct Current).

Yes, a current will be induced in coil B.**

• Reason: When the electric current in coil A is varied (switched on/off or changed using a rheostat), the magnetic field produced around coil A changes.
• Since coil B is placed in close proximity, the magnetic flux lines linked with coil B also change continuously.
• According to the principle of Electromagnetic Induction, this changing magnetic flux induces an electric current in coil B.

(a) Moved inside: The galvanometer needle shows a momentary deflection in one direction**, indicating the generation of an induced current.

• (b) Kept stationary: The galvanometer needle shows zero deflection (no current), because there is no relative motion and no change in magnetic flux.
• (c) Moved outwards: The galvanometer needle shows a momentary deflection in the opposite direction, indicating that current is induced in the reverse direction.

The direction of magnetic field lines produced by a straight conductor is given by Right-Hand Thumb Rule (or Maxwell’s Corkscrew Rule)

• Right-Hand Thumb Rule: Imagine holding the current-carrying straight conductor in your right hand such that the thumb points in the direction of electric current. Then, the fingers wrapped around the conductor point in the direction of the magnetic field lines.

Materials required:** A long soft iron nail/core, insulated copper wire, battery, key, paper clips/pins.

• Procedure:

1. Wind the insulated copper wire tightly around the soft iron nail in several circular turns.
2. Connect the two free ends of the copper wire to a battery through a switch/key.
3. Close the switch to pass current. Bring paper clips near the nail; they get attracted to the nail, showing it has become an Electromagnet.
4. Open the switch; the clips fall off immediately as magnetism disappears.