Magnetic Effects of Elect. Current Imp. Questions Class 10 Science

Magnetic Effects of Electric Current, basically Ch 12 of the CBSE Class 10 Science syllabus, is an intriguing part of the subject that bridges the gap between electricity and magnetism. This chapter explains how electric current produces magnetic fields and how these fields influence conductors. Understanding these concepts not only tells us about the basics of electromagnetism but also demonstrates the practical applications of magnetic effects in devices like motors, generators, and transformers.

This Ch 12 Science Class 10 Important Questions has a direct linkage with the physics chapters of classes 11 and 12, you must study this chapter in detail if you want to excel in higher physics or other science subjects.

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Chapter 12 Magnetic Effects of Electric Current: Important Questions

1. 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.

2. 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.

3. 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.

4. 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.

5. 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. 

6. 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.

Key Concepts in Magnetic Effects of Electric Current, Ch 12, Class 10

The chapter explores the relationship between electricity and magnetism, revealing how electric currents produce magnetic fields. These ideas form the foundation for understanding modern electrical systems and technologies; the key concepts include:

Magnetic Field and Its Properties: A magnetic field is the region around a magnet or current-carrying conductor where the magnetic force can be detected.

Magnetic field lines: These are imaginary lines that represent the direction and strength of the magnetic field. Key properties include:

• They emerge from the North Pole and merge at the South Pole.
• They never intersect.
• Closer lines indicate stronger fields.

Magnetic Field Due to a Current-Carrying Conductor: Current produces a magnetic field around the conductor, and its direction can be determined using the right-hand thumb rule.

Magnetic Field for a Straight Conductor: Circular magnetic field lines form around the conductor.

Magnetic Field for a Circular Loop: The field becomes stronger at the centre of the loop due to overlapping field lines.

Force on a Current-Carrying Conductor in a Magnetic Field: When a conductor carrying current is placed in a magnetic field, it experiences a force.

The direction of the force is given by Fleming’s Left-Hand Rule. This principle is utilised in electric motors.

Electromagnetic Induction: When a conductor moves through a magnetic field or the magnetic field around a conductor changes, an electromotive force (EMF) is induced.

This is explained by Faraday’s Law of Electromagnetic Induction. Applications include generators and transformers.

Domestic Electric Circuits: Concepts such as earthing, fuses, and circuit breakers are discussed to highlight safety measures in electrical systems.

Important Applications of Magnetic Effects

Magnetic effects of electric current have numerous real-world applications that are integral to modern technology and daily life. Here are some of the most important applications:

1. Electric Motors - Electric motors are devices that convert electrical energy into mechanical energy using magnetic fields. They play a crucial role in various machines and appliances, including:

• Fans and Air Conditioners: Motors drive the blades to circulate air efficiently.
• Washing Machines: Motors enable the rotation of drums for cleaning clothes.
• Pumps: Electric motors power water pumps used in homes and industries.
• Industrial Machines: Motors are used in conveyor belts, compressors, and other heavy machinery.

The principle of operation relies on the force experienced by a current-carrying conductor in a magnetic field, explained by Fleming's Left-Hand Rule.

2. Electric Generators - Electric generators are devices that convert mechanical energy into electrical energy using the principle of electromagnetic induction. They are the backbone of electricity generation and supply, powering homes, industries, and businesses.

• Power Plants: Generators in hydroelectric, thermal, and wind power plants produce electricity on a large scale.
• Backup Systems: Portable generators are used during power outages for essential services.
• Renewable Energy Systems: Wind turbines and hydropower setups use generators to harness natural energy sources.

Generators function based on Faraday’s Law of Electromagnetic Induction, which states that an electromotive force (EMF) is induced when a conductor moves through a magnetic field.

3. Transformers: Transformers are devices that use magnetic effects to change the voltage levels of alternating current (AC). They are essential for the efficient transmission and distribution of electricity.

• Step-Up Transformers: Increase voltage to reduce energy loss during long-distance transmission of electricity.
• Step-Down Transformers: Decrease voltage to safe levels for residential and industrial use.
• Electronic Devices: Miniature transformers are used in devices like chargers and adapters to provide the required voltage levels.

Transformers operate on the principle of mutual induction, where a changing current in one coil induces a voltage in another coil through a magnetic field.

4. Magnetic Levitation (Maglev) - Magnetic levitation involves using magnetic fields to lift and propel objects without direct contact, reducing friction significantly.

• High-Speed Trains: Maglev trains, like those in Japan and China, use powerful electromagnets to achieve speeds of over 600 km/h while ensuring a smooth ride.
• Industrial Applications: Magnetic levitation is used in conveyor systems, precision engineering, and reducing wear and tear in machinery.
• Medical Equipment: Devices like MRI machines use similar principles for non-invasive imaging techniques.

This application showcases the efficiency and innovation made possible by harnessing magnetic fields.

These applications highlight the versatility and importance of magnetic effects in driving modern technology. Knowing these principles not only helps in academic success but also provides insight into their practical importance in shaping the world around us.

Tips for Preparing Chapter 12

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.

By mastering rules, practicing diagrams, solving numericals, and relating concepts to practical applications, you’ll be well-prepared to tackle any question from CBSE Class 10 Chapter 12 with confidence. The concepts in Magnetic Effects of Electric Current are fundamental to understanding how electricity and magnetism are interconnected. These principles are important in modern technology, from generating electricity to designing efficient machines. Mastering this chapter not only prepares you for exams but also helps you appreciate the role of electromagnetism in everyday life. With a strong knowledge of the basics and regular practice, you can confidently tackle any question related to this topic. Happy learning!

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

All the best!