Important Questions Ch12 Class 10 Science Magnetic Effects of Electric Current

The chapter Magnetic Effects of Electric Current is one of the most conceptually rich and practical topics in Class 10 Physics. It explains how electricity and magnetism are related and how electric current can produce magnetic fields. 

This chapter not only helps you understand magnetic field patterns and the working of electromagnetic devices but also connects real-life applications like household appliances and transportation systems to scientific laws.

The Magnetic Effects of Electric Current Important Questions for Class 10 Physics are designed to help you:

• Strengthen understanding of magnetic field concepts and laws.
• Practice diagram-based and reasoning questions.
• Prepare thoroughly for CBSE exams with conceptual clarity and practical examples.

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Chapter 12 Magnetic Effects of Electric Current: Important Questions

Q1. Arun built a DC electric motor using whatever scrap material he had. Since he did not have a split ring, he used a full ring in contact with the brushes.

State what will be the effect of using a full ring on the movement of the axle in Arun's motor. Give a reason for your answer.

Answer: If Arun uses a full ring instead of a split ring in his DC motor, the axle of the motor will not rotate continuously. Here's why:

The split ring (commutator) is crucial for reversing the direction of current in the coil every half-turn. This reversal ensures that the torque acting on the coil remains in the same direction, allowing the motor to rotate continuously.

However, with a full ring:

• The direction of current through the coil will not change as the coil rotates.
• This means that after the coil passes the vertical position, the forces on the coil will oppose its motion rather than sustain it, causing the coil to oscillate back and forth instead of completing continuous rotations.

In summary, the use of a full ring prevents continuous rotation because it does not reverse the current in the coil as required for proper motor operation.

Q2. An induction cooktop works on the principle of electromagnetic induction. Inside the cooktop there is a tightly wound metal coil. An alternating current flows through the coil and produces an invisible, high-frequency, alternating magnetic field all around it.

When a vessel made of magnetic material is placed on the cooktop, the magnetic field produced by the coil penetrates the iron of the vessel and induces whirling electrical (eddy) currents inside the pan and makes it hot.There is no open flame used. Heat from the pan flows directly into the food or water inside it (by conduction) without heating up the area surrounding the cooktop. Unless there is a pan on the cooktop, no heat is produced.

List any two advantages, with reasons, of cooking using an induction cooktop instead of a gas stove.

Answer: Here are two advantages of cooking using an induction cooktop instead of a gas stove:

Energy Efficiency: In an induction cooktop, heat is directly generated in the vessel through electromagnetic induction. This minimizes heat loss to the surroundings, making the process more energy-efficient compared to a gas stove, where significant heat is lost to the air around the flame.

Safety: Induction cooktops do not use an open flame, reducing the risk of burns or accidental fires. Additionally, they only generate heat when a suitable vessel is placed on the cooktop, adding an extra layer of safety, especially in households with children.

These features make induction cooktops a more efficient and safer cooking option.

Q3. The figure shows two magnets X and Y kept near each other. Their poles are not marked, but the magnetic field lines are shown in the figure.

If magnet X is moved towards magnet Y as indicated by the arrow, will the two magnets attract or repel each other? Justify your answer by describing how you interpret the field lines.

Answer: From the diagram of the magnetic field lines:

• Magnetic field lines always emerge from the north pole of a magnet and enter the south pole.
• In the region between the two magnets, the field lines from magnet X are entering magnet Y, indicating that the pole of X near Y is a north pole and the pole of Y near X is a south pole.

Since opposite poles attract each other, the two magnets will attract each other when magnet X is moved closer to magnet Y. The interpretation of the magnetic field lines shows that the poles facing each other are opposite in polarity (north pole of X and south pole of Y). This alignment causes an attractive force between the two magnets.

Q4. In a DC motor with a commutator, how many times does

(i) the current in the armature coil change its direction during one rotation of the coil, 

(ii) the current stop flowing in the armature coil during one rotation of the coil?

Answer: (i) The current in the armature coil changes direction twice during one complete rotation.

This happens because the commutator switches the direction of the current at the point where the coil passes through the neutral position (when the coil is aligned with the magnetic field of the stator). The commutator reverses the current flow in the coil every half turn to maintain continuous rotation of the armature.

(ii) The current never completely stops flowing during one rotation in a properly functioning DC motor with a commutator.

The commutator ensures that there is always a path for the current to flow, even when the coil is at the neutral position where the current direction is reversed. The commutator continuously switches the current direction as needed, maintaining a constant flow of current.

Q5. You are given three identical 10 ohm resistors and a 12 V cell.

Draw the circuit diagram to show how the resistors can be connected with the 12 V cell so that the total heat produced in the circuit is the MINIMUM.

Answer: To minimize the total heat produced in the circuit, you should connect the resistors in series. 

Q6. A current clamp is an electrical device used to measure current in a conductor without making any physical contact with the conducting part of the conductor. The current clamp has jaws that clamp around the conductor as shown below.

Some current clamps work on the principle of electromagnetic induction and hence can measure only alternating current. Give a reason why direct current cannot be measured by these current clamps.

Answer: Direct current (DC) cannot be measured by current clamps that work on the principle of electromagnetic induction because electromagnetic induction only occurs with a changing magnetic field.

• Alternating Current (AC): In AC, the current constantly changes direction and magnitude, which leads to a continuously changing magnetic field around the conductor. This changing magnetic field induces a current in the sensing coil of the current clamp, allowing the measurement of the AC current.
• Direct Current (DC): In DC, the current flows in a constant direction with a steady magnitude. This results in a constant magnetic field around the conductor. Since there is no change in the magnetic field, no induction occurs in the current clamp, making it impossible for the clamp to detect the current.

Therefore, current clamps that rely on electromagnetic induction can only detect alternating current (AC), not direct current (DC), because DC does not produce the fluctuating magnetic field required for induction.

Some More Important Question Answers of Class 10 Magnetic Effects of Electric Current

Q1. What happens when current flows through a conductor?

Answer: When an electric current passes through a conductor, a magnetic field is produced around it. This was discovered by Hans Christian Ørsted in 1820. He noticed that a compass needle placed near a current-carrying wire got deflected. This proved that electricity and magnetism are related.

Q2. What are magnetic field lines? State their properties.

Answer: Magnetic field lines are imaginary lines used to represent a magnetic field. Here are the Properties:

1. Field lines emerge from the north pole and enter the south pole.
2. They form closed loops (inside the magnet they go from south to north).
3. The direction of the field is given by the tangent to the field line.
4. The closer the lines, the stronger the field.
5. Field lines never cross each other.

Q3. Explain the right-hand thumb rule.

Answer: Hold a current-carrying conductor in your right hand with the thumb pointing in the direction of current. The direction in which your curled fingers point gives the direction of the magnetic field around the conductor.

Q4. Describe the magnetic field produced by a straight current-carrying conductor.

Answer: The magnetic field forms concentric circles around the wire, with the wire as the center. The strength of the field increases with current and decreases with distance from the wire.

Q5. How can the direction of the magnetic field be determined around a straight wire?

‍Answer: By using the right-hand thumb rule:

• If the current is upward, the field is anticlockwise.
• If the current is downward, the field is clockwise.

Q6. What is the magnetic field at the centre of a circular coil carrying current?

‍Answer: Field lines around a circular coil are circular near the wire, but at the centre they combine to give a strong magnetic field along the axis of the coil. Direction is found by the right-hand rule: curl fingers in current direction, thumb shows field direction.

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Q7. What is a solenoid? Describe its magnetic field.

Answer: A solenoid is a long coil of wire wound in the form of a cylinder. When current flows, it produces a uniform magnetic field inside, similar to a bar magnet: one end acts as north, the other as south. The strength increases with:

• number of turns,
• current,
• inserting an iron core.

Q8. How can you show that a current-carrying conductor in a magnetic field experiences a force?

Answer: Experiment: Place a wire between the poles of a magnet. When current flows, the wire is deflected. Reversing current or field reverses the direction of force.

Q9. State Fleming’s Left-Hand Rule.

Answer: Stretch the thumb, forefinger, and middle finger of your left hand mutually perpendicular:

• Forefinger → field (N to S)
• Middle finger → current (+ to −)
• Thumb → force/motion

This is used to find direction of motion in electric motors.

Q10. Derive the formula for force on a current-carrying conductor in a magnetic field.

Answer: Force depends on:

• current (I),
• length of conductor (L),
• strength of field (B),
• angle θ between conductor and field. Formula: F = BIL sinθ

Maximum force when conductor is perpendicular to the field (θ = 90°).

Q11. State the principle of an electric motor.

Answer: A current-carrying conductor in a magnetic field experiences a force. In a motor, a rectangular coil rotates continuously because forces on opposite sides form a couple.

Q12. Explain the working of an electric motor.

Answer:

1. The motor has a rectangular coil placed between the poles of a magnet.
2. Current enters the coil through a commutator and brushes.
3. Forces act on the two arms in opposite directions → coil rotates.
4. Commutator reverses current every half turn → continuous rotation.

Applications: used in fans, mixers, pumps.

Q13. What is electromagnetic induction?

Answer: The process of producing current in a coil due to a changing magnetic field is called electromagnetic induction. It was discovered by Faraday.

Q14. How can current be induced in a coil?

Answer: By:

1. Moving a magnet towards or away from the coil.
2. Moving the coil towards or away from the magnet.
3. Changing current in a nearby coil.

Q15. State Fleming’s Right-Hand Rule.

Answer: Stretch the thumb, forefinger, and middle finger of right hand perpendicular:

• Forefinger → field
• Thumb → motion of conductor
• Middle finger → induced current

This is used for direction of induced current in generators.

Q16. Explain the principle and working of an electric generator.

Answer:
Principle: Electromagnetic induction - current is induced in a coil rotating in a magnetic field.
Working:

1. A coil rotates between poles of a magnet.
2. Coil cuts magnetic field lines → current induced.
3. Brushes and slip rings deliver current to the external circuit. Generators can produce AC or DC current.

Q17. Differentiate between AC and DC.

Answer:

• AC (alternating current): changes direction periodically, used in homes. Frequency in India = 50 Hz.
• DC (direct current): flows in one direction only, supplied by batteries and cells.

Q18. What is the role of a fuse in a household circuit?

Answer: Fuse is a safety device made of wire with low melting point. If current exceeds safe limit, fuse melts and breaks circuit, protecting appliances from damage.

Q19. Why are appliances in homes connected in parallel?

Answer:

1. All get the same voltage (220 V).
2. If one appliance fails, others work.
3. Each can be switched on/off independently.

Q20. What are the main safety measures in household wiring?

Answer:

1. Earthing: prevents shock by directing leakage current to ground.
2. Fuses or MCBs: break circuit in case of overload.
3. Appliances connected in parallel.

Video Lecture: Must-watch for Quick Revision

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Extra Questions for practice!

Q1. Who discovered the magnetic effect of current? Explain the experiment.

Q2. Draw magnetic field lines around a bar magnet.

Q3. Explain with a diagram how a solenoid acts as a bar magnet.

Q4. Write two factors affecting the strength of magnetic field in a solenoid.

Q5. Why does a compass needle deflect near a current-carrying wire?

Q6. Explain why current reverses direction every half turn in a motor.

Q7. Define electromagnetic induction with an activity.

Q8. Draw a labelled diagram of an AC generator.

Q9. Differentiate between fuse and MCB.

Q10. Why is earthing important in electrical appliances?

How to Ace These Class 10 Magnetic Effects of Electric Current Important Questions

This chapter is best learned through a mix of theory, diagrams, and applications. Follow these steps to prepare effectively:

Step 1: Understand Magnetic Field and Its Representation

Begin by learning what a magnetic field is and how its direction is represented using field lines. Study the properties of magnetic field lines - they never intersect, and their closeness indicates field strength.

Step 2: Learn the Right-Hand Thumb Rule

This rule helps determine the direction of the magnetic field around a current-carrying conductor. Hold your right hand with the thumb pointing in the direction of current, and the curl of your fingers shows the magnetic field’s direction.

Step 3: Study the Magnetic Field Due to a Straight Conductor and a Circular Loop

Know how magnetic field patterns change with conductor shape. Practise drawing neat field diagrams for both cases, showing the direction of field lines.

Step 4: Understand the Magnetic Field Due to a Solenoid

Learn how a solenoid behaves like a bar magnet, with distinct north and south poles. Study its use in creating strong magnetic fields in devices such as electromagnets.

Step 5: Study Fleming’s Left-Hand and Right-Hand Rules

• Fleming’s Left-Hand Rule: Used to find the direction of force on a current-carrying conductor in a magnetic field (used in motors).
• Fleming’s Right-Hand Rule: Used to find the direction of induced current in a conductor moving through a magnetic field (used in generators).

Step 6: Learn the Principle and Working of Electric Motor

Study the construction and working of an electric motor, including its main parts: coil, commutator, brushes, and magnets. Practise drawing its labeled diagram neatly.

Step 7: Learn Electromagnetic Induction and Electric Generator

Understand how current is induced when a conductor moves in a magnetic field. Study the construction and working of a simple electric generator and its difference from a motor.

Step 8: Revise Domestic Circuit and Safety Devices

Learn the basic layout of the domestic circuit, including live, neutral, and earth wires. Study safety devices such as fuses and circuit breakers (MCBs).

Tips for Preparing Chapter 12 These Magnetic Effects of Electric Current Ques/Ans.

Chapter 12, Magnetic Effects of Electric Current, involves key principles of electromagnetism and their applications. To study this chapter better than ever, follow these preparation tips:

Master Key Rules and Laws

• Fleming’s Left-Hand Rule: Essential for understanding the force on a current-carrying conductor in a magnetic field (used in electric motors).
• Right-Hand Thumb Rule: Helps determine the direction of the magnetic field around a current-carrying conductor.
• Faraday’s Law of Electromagnetic Induction: Understand its significance in generators and transformers, including how EMF is induced.

Practice Diagrams

• Familiarise yourself with diagrams showing magnetic field patterns around straight conductors, circular loops, and solenoids.
• Be confident in drawing and labelling devices like electric motors, generators, and transformers. Neat and accurate diagrams often fetch extra marks in exams.

Understand Practical Applications

• Relate theoretical concepts to devices like motors, generators, and transformers to understand their working.
• Focus on the role of magnetic fields in domestic circuits, including safety devices like circuit breakers and fuses. This helps connect theory with real-world scenarios.

Solve Numerical Problems

• Practice problems related to magnetic force on conductors. Magnetic fields produced by currents. Induced EMF and its calculations using Faraday’s Law.
• Ensure a step-by-step approach to numerical questions for clarity and accuracy.

Revise Regularly

• Consistently review textbook exercises, NCERT exemplar problems, and CBSE sample papers.
• Pay attention to past exam questions to identify frequently tested topics and patterns.

We hope that you practise the above Magnetic Effect Of Electric Current Extra Questions and achieve your dream marks.

FAQs

Q1. How many marks are generally allotted to this chapter in Class 10 board exams?

Ans. This chapter usually carries 8 to 10 marks, including one or two reasoning-based and diagram questions.

Q2. Which topics are most important for board exams?

Ans. Magnetic field lines, Right-Hand and Left-Hand Rules, the working of an electric motor and generator, and electromagnetic induction are the most important topics.

Q3. Are diagrams compulsory in this chapter?

Ans. Yes, diagrams are very important. Labeled diagrams of the motor, generator, solenoid, and field lines are frequently asked and carry full marks when drawn neatly.

Q4. How can I easily remember the difference between Fleming’s rules?

Ans. Remember that Left-Hand Rule is for motors (current produces motion) and Right-Hand Rule is for generators (motion produces current).

Q5. How can I prepare this chapter effectively before exams?

Ans. Revise all key rules, draw each diagram twice, and practise short notes summarizing each topic. Focus on conceptual clarity instead of memorizing definitions.