NCERT Solutions Class 10 Science Chapter 9 Magnetic Effects of Electric Current
NCERT Solutions Class 10 Science Chapter 9 Magnetic Effects of Electric Current offer comprehensive, step-by-step explanations designed to help students master fundamental electromagnetism concepts for CBSE Board examinations. This chapter bridges the gap between electricity and magnetism, covering essential topics such as magnetic field lines, Oersted's discovery, magnetic field patterns around current-carrying conductors, Fleming's Left-Hand Rule, and domestic electric circuits. With an average weightage of 6 to 8 marks in the Class 10 Science board paper, preparing these NCERT Science Class 10 solutions thoroughly ensures clarity in both theoretical definitions and analytical numerical problems.
Chapter Overview
The NCERT Solutions Class 10 Science Chapter on Magnetic Effects of Electric Current explores how an electric current creates a magnetic field in its surrounding space, and conversely, how magnetic fields exert mechanical forces on moving charges and current-carrying conductors. The core syllabus prescribed by CBSE covers the following key areas:
- Magnetic Field and Field Lines: Representation of magnetic fields using continuous closed curves, properties of magnetic lines of force, and the magnetic field of a bar magnet.
- Magnetic Field due to a Current-Carrying Conductor: Field geometry around a straight conductor (Right-Hand Thumb Rule), a circular loop, and a long cylindrical coil (solenoid).
- Electromagnets and Permanent Magnets: Construction, magnetic core materials (soft iron), properties, and industrial applications.
- Force on a Current-Carrying Conductor in a Magnetic Field: Mutual interaction of magnetic fields, maximum force condition, and Fleming's Left-Hand Rule.
- Domestic Electric Circuits: Live wire, neutral wire, earth wire safety mechanism, potential difference (220 V in India), series vs. parallel wiring, short-circuiting, overloading, and safety fuses.
In the CBSE Class 10 board examination, questions from this chapter test conceptual understanding through circuit diagrams, direction-finding application questions using hand rules, reasoning-based short answer questions, and numerical calculations related to domestic power ratings and safety fuses.
NCERT In-Text Questions and Step-by-Step Solutions
In-Text Questions (Page-Wise Solutions)
Set 1: Basic Properties of Magnetism
Question 1: Why does a compass needle get deflected when brought near a bar magnet?
Solution:
A compass needle is essentially a small, pivoted permanent bar magnet. The ends of the compass needle point approximately towards the north and south geographic directions. When brought near a bar magnet, the magnetic field of the bar magnet exerts a mechanical torque (force) on the magnetic poles of the compass needle. Like poles repel each other while unlike poles attract each other, causing the needle to deflect and align itself along the net magnetic field line at that point.
Set 2: Magnetic Field Lines and Properties
Question 1: Draw magnetic field lines around a bar magnet.
Solution:
Magnetic field lines around a standard bar magnet emerge from the North pole and enter the South pole outside the magnet, forming continuous closed loops by running from South to North inside the magnet body. The lines are crowded near the poles where the field strength is strongest.
Question 2: List the properties of magnetic lines of force.
Solution:
- Magnetic field lines originate from the North pole and terminate at the South pole outside the magnet. Inside the magnet, their direction is from the South pole to the North pole.
- Magnetic field lines are continuous, smooth closed curves.
- The degree of closeness (crowding) of the field lines is a measure of the strength of the magnetic field (flux density).
- The tangent drawn at any point on a magnetic field line gives the direction of the magnetic field vector (B) at that point.
- Two magnetic field lines never intersect each other.
Question 3: Why don't two magnetic lines of force intersect each other?
Solution:
If two magnetic field lines were to intersect at a given point, a compass needle placed at that intersection point would have to point in two different directions simultaneously. This is physically impossible because the magnetic field at any single point in space has a unique, definite resultant direction.
Set 3: Magnetic Field due to Current-Carrying Conductors
Question 1: A current through a horizontal power line flows in east to west direction. What is the direction of magnetic field at a point directly below it and at a point directly above it?
Solution:
According to the Right-Hand Thumb Rule:
- Imagine grasping the horizontal wire with your right hand such that your thumb points towards the west (direction of electric current).
- The curled fingers wrap around the wire.
- At a point directly below the wire: The curled fingers point towards the North direction.
- At a point directly above the wire: The curled fingers point towards the South direction.
Final Answer: Directly below: North; Directly above: South.
Set 4: Force on a Conductor in a Magnetic Field
Question 1: Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer)
(a) mass (b) speed (c) velocity (d) momentum
Solution:
When a charged particle like a proton moves in a magnetic field, the magnetic force acts perpendicular to its direction of motion. Because the force is perpendicular to velocity, it alters only the direction of motion without changing the magnitude of velocity (speed). Since velocity and momentum are vector quantities that depend on direction, both velocity and momentum change continuously.
Correct Options: (c) velocity and (d) momentum
Question 2: A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is:
(a) towards south (b) towards east (c) downward (d) upward
Solution:
We apply Fleming's Left-Hand Rule:
- Middle finger (Current direction): Points West (since an α-particle is positively charged, current direction matches its velocity).
- Thumb (Force / Deflection direction): Points North.
- Forefinger (Magnetic field direction): Points perpendicularly Upward (out of the page).
Correct Option: (d) upward
Set 5: Domestic Electric Circuits
Question 1: Name two safety measures commonly used in electric circuits and appliances.
Solution:
- Electric Fuse (or Miniature Circuit Breaker - MCB): Protects circuits and electrical appliances against overloading and short-circuiting by breaking the circuit when current exceeds the safe limit.
- Earth Wire (Earthing): Connects the metallic casing of high-power appliances to the ground, providing a low-resistance path for leakage currents and preventing lethal electric shocks.
Question 2: What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Solution:
The green-insulated earth wire is connected to a metal plate buried deep inside the earth near the premises. Its primary function is to serve as a low-resistance return path for electric current.
When the live wire inside an electrical appliance (such as an electric iron, refrigerator, or washing machine) accidentally touches its metallic body, the earth wire channels the leakage current directly into the earth. This ensures that the potential of the metal body remains equal to that of the earth (zero potential), thereby protecting the user from severe electric shocks.
NCERT Chapter-End Exercise Solutions
Here are comprehensive, step-by-step CBSE NCERT solutions for all the exercise questions at the end of Chapter 9.
Exercise Questions and Detailed Working
Question 1: Which of the following correctly describes the magnetic field near a long straight wire?
(a) The field consists of straight lines perpendicular to the wire.
(b) The field consists of straight lines parallel to the wire.
(c) The field consists of radial lines originating from the wire.
(d) The field consists of concentric circles centred on the wire.
Answer: (d) The field consists of concentric circles centred on the wire.
Reasoning: When an electric current flows through a long straight conductor, the magnetic lines of force form concentric circular loops in planes perpendicular to the conductor, centered along the axis of the wire.
Question 2: At the time of short circuit, the current in the circuit:
(a) reduces substantially.
(b) does not change.
(c) increases heavily.
(d) vary continuously.
Answer: (c) increases heavily.
Reasoning: A short circuit occurs when the live wire and neutral wire come into direct physical contact. The resistance of the circuit drops almost to zero (R ≈ 0). According to Ohm's Law (I = V/R), the current (I) surges to an extremely large value.
Question 3: State whether the following statements are True or False:
(a) The field at the centre of a long circular coil carrying current will be parallel straight lines.
(b) A wire with a green insulation is usually the live wire of an electric supply.
Answer:
(a) True. At the center of a circular loop/solenoid, the magnetic field lines are straight and parallel, indicating a uniform magnetic field.
(b) False. In standard domestic wiring, green insulation represents the earth wire, while red insulation represents the live wire and black insulation represents the neutral wire.
Question 4: List two methods of producing magnetic fields.
Solution:
- By using permanent magnets (e.g., bar magnet, horseshoe magnet).
- By passing an electric current through a conductor (e.g., straight wire, circular loop, or solenoid).
- By moving a charged particle or using varying electric fields.
Question 5: How does a solenoid behave like a magnet? Can you determine the north and south poles of a current-carrying solenoid with the help of a bar magnet? Explain.
Solution:
A solenoid is a long coil containing a large number of close turns of insulated copper wire wrapped in the shape of a cylinder. When an electric current passes through the solenoid, magnetic field lines are generated around and inside it.
- Inside the solenoid, the field lines are parallel straight lines, representing a uniform magnetic field.
- Outside the solenoid, the field lines emerge from one end and enter the other end, exactly resembling the magnetic field pattern of a bar magnet.
Determining Polarity with a Bar Magnet:
Suspend the current-carrying solenoid freely or bring a known bar magnet near one of its ends. Bring the known North pole of the bar magnet near one end of the energized solenoid:
- If the end of the solenoid is repelled by the North pole of the bar magnet, that end of the solenoid is its North pole.
- If that end is attracted, it is the South pole of the solenoid (since like poles repel and unlike poles attract).
Question 6: When is the force experienced by a current-carrying conductor placed in a magnetic field largest?
Solution:
The magnitude of magnetic force on a current-carrying conductor is given by the formula:
F = B · I · L · sin θ
Where:
- B = Magnetic field strength
- I = Current in the conductor
- L = Length of the conductor in the field
- θ = Angle between the conductor and the magnetic field vector
The force is maximum when sin θ = 1, which occurs when θ = 90°. Therefore, the force is largest when the current-carrying conductor is placed perpendicular to the direction of the magnetic field.
Question 7: Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?
Solution:
Let us determine the given parameters step by step:
- Direction of electron motion: From back wall to front wall.
- Direction of conventional current (I): Opposite to electron motion → From front wall to back wall.
- Direction of deflection / Force (F): Towards the right side.
Applying Fleming's Left-Hand Rule:
- Stretch the thumb, forefinger, and middle finger of your left hand mutually perpendicular to each other.
- Align the middle finger pointing towards the back wall (direction of current).
- Align the thumb pointing towards the right side (direction of magnetic force).
- The forefinger naturally points vertically downwards.
Final Answer: The magnetic field is directed vertically downwards.
Question 8: State the rule to determine the direction of a:
(i) magnetic field produced around a straight conductor-carrying current,
(ii) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it.
Solution:
(i) Right-Hand Thumb Rule (Maxwell's Corkscrew Rule):
Imagine holding a current-carrying straight conductor in your right hand such that your thumb points in the direction of electric current. Then, the direction in which your fingers curl around the conductor gives the direction of the magnetic field lines.
(ii) Fleming's Left-Hand Rule:
Stretch the thumb, forefinger, and middle finger of the left hand such that they are mutually perpendicular to each other. If the forefinger points in the direction of the external magnetic field and the middle finger points in the direction of the electric current, then the thumb points in the direction of motion or mechanical force acting on the conductor.
Question 9: When does an electric short circuit occur?
Solution:
An electric short circuit occurs when:
- The insulation of wires gets damaged due to wear, aging, or overheating.
- There is a fault in an electrical appliance causing the live wire and the neutral wire to come into direct physical contact.
As a result, circuit resistance drops almost to zero, leading to an extremely high current surge that causes intense sparking, heat generation, and potential fire hazards.
Question 10: An electric oven of 2 kW power rating is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.
Solution:
Given:
- Power rating of electric oven (P) = 2 kW = 2000 W
- Supply voltage (V) = 220 V
- Current rating of the circuit = 5 A
To Find:
- Current drawn by the oven (I) and operational outcome.
Formula:
P = V × I ⇒ I = P / V
Substitution and Calculation:
I = 2000 W / 220 V = 100 / 11 A ≈ 9.09 A
Conclusion:
The current drawn by the electric oven (9.09 A) is significantly higher than the safe current rating of the circuit (5 A). Consequently, the circuit gets overloaded. The high current generates excess Joule heat, which causes the electric fuse wire to melt and break the circuit (or trips the MCB), preventing appliance damage and fire.
Final Answer: Current drawn is 9.09 A; the 5 A fuse will melt and break the circuit due to overloading.
Question 11: What precaution should be taken to avoid the overloading of domestic electric circuits?
Solution:
- Avoid connecting too many high-power appliances (such as air conditioners, geysers, heaters, and electric irons) to a single multi-plug socket simultaneously.
- Use separate power circuits: Use 5 A rating circuits for low-power devices (bulbs, fans, TVs) and dedicated 15 A rating circuits for heavy appliances (refrigerators, ACs, heaters).
- Ensure quality wiring: Use standard, high-grade insulated copper cables of appropriate gauge.
- Install safety devices: Always integrate properly rated safety fuses or Miniature Circuit Breakers (MCBs) in the live wire.
- Periodic electrical inspection: Replace worn-out or damaged wires promptly to prevent unintentional short circuits.
Important Formulas, Rules, and Principles
To score full marks in numerical and application questions of NCERT Solutions Class 10 Science, keep this summary table handy:
| Concept / Rule | Governing Formula / Principle | Primary Application |
|---|---|---|
| Right-Hand Thumb Rule | Thumb → Current (I) Curled Fingers → Magnetic Field (B) |
Finding magnetic field direction around straight wires and circular loops. |
| Magnetic Field of Straight Conductor | B ∝ I and B ∝ (1 / r) | Calculating relative magnetic field strength with changing current or distance. |
| Magnetic Field inside a Solenoid | B = μ0 · n · I (Uniform field) | Electromagnet design; field inside long coils. |
| Magnetic Force on Conductor | F = B · I · L · sin θ | Force calculation; maximum at θ = 90°, zero at θ = 0°. |
| Fleming's Left-Hand Rule | Forefinger → Field (B) Middle finger → Current (I) Thumb → Force / Motion (F) |
Determining deflection direction of current-carrying rods and charged beams. |
| Domestic Current Calculation | I = P / V | Evaluating circuit safety, fuse ratings, and overloading checks. |
Common Mistakes and Tips for CBSE Class 10 Board Exams
- Confusing Right-Hand Thumb Rule with Fleming's Left-Hand Rule: Remember that the Right-Hand Thumb Rule determines the direction of magnetic field lines generated by a current, whereas Fleming's Left-Hand Rule determines the direction of mechanical force/motion experienced by a conductor placed in an external magnetic field.
- Drawing Intersecting Field Lines: In diagram-based questions, never let magnetic field lines cross or touch each other. Field lines must be shown as smooth, concentric circles or continuous closed loops.
- Direction of Moving Negative Charges (Electrons): When dealing with alpha particles or protons (positive charges), current direction is identical to their velocity. When dealing with electrons or beta particles (negative charges), the conventional current direction is opposite to their direction of motion.
- Overlooking the Fuse Placement: An electric fuse must always be connected in series with the live wire, never the neutral wire. If connected to the neutral wire, melting the fuse would interrupt the current, but the appliance would still remain at high live potential (220 V), posing an electric shock risk.
- Incomplete Working in Numericals: Always state Given, To Find, Formula, Substitution, and Final Answer with SI Units (e.g., Amperes 'A', Volts 'V', Watts 'W') to secure full step marks.
Board Exam Relevance and Marking Scheme
In the CBSE Class 10 Science board examination, Chapter 9 carries between 6 to 8 marks. The questions are structured across multiple formats:
- Section A (1 Mark - MCQs & Assertion-Reasoning): Tests core factual knowledge, such as the behavior of magnetic field lines inside a solenoid, identification of wire insulation colors, or hand-rule direction questions.
- Section B & C (2 & 3 Marks - Short Answer): Involves sketching magnetic field line patterns (around a bar magnet, circular loop, or solenoid), stating rules with clear statements, and explaining the earthing safety mechanism.
- Section D / E (4 & 5 Marks - Long Answer & Case-Based Questions): Frequently features practical scenarios such as appliance power overloading calculations (e.g., oven or heater on a 5 A line), distinction between electromagnets and permanent magnets, or multi-step deflection questions using Fleming's Left-Hand Rule.
More NCERT Solutions and Practice
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