Chapter 13

Magnetic Effects Of Electric Current

 

Introduction

When a compass is brought close to an electrical current coil, the needle deflects due to the magnetic field created by the electric current. A magnet is a molecule with the ability to attract iron and nickel, as well as other metals and nickel-based materials, towards it. The North Pole and the South Pole are the two poles of a magnet.

In this chapter, we will learn about the following topics: 

  • Magnetic field
  • Field lines
  • Electromagnet
  • The right-hand thumb rule
  • The magnetic field through circular loops

To begin with, let us understand some basics of the chapter.

What are the magnetic fields?

The magnetic field is the zone around a magnet in which the magnet's force may be observed or sensed. Magnetism is a vector quantity since it has both a magnitude and a direction.

What are magnetic field lines?

The magnetic field that surrounds a magnet creates a pattern known as field lines. Field lines are graphical or pictorial representations of the magnetic field's direction and magnitude around a magnet.

What is an electromagnet?

When electricity passes through a conductor, it begins to act like a magnet. An electromagnet is a name given to an electricity-conducting conductor.

What is the right-hand thumb rule?

The Right-Hand Thumb Rule asserts that if you hold electrical conductors in your right hand with your thumb pointing in the direction of the current, your fingers will wrap around it in the direction of the magnetic field lines.

Questions:

Question 1: Which of the following statements accurately characterises the magnetic field near a long straight wire?

(i) The field is made up of straight lines that are perpendicular to the wire.

(ii) The field is made up of straight lines that run parallel to the wire.

(iii) The field is made up of radial lines that radiate from the wire.

(iv) The field is made up of concentric circles centred on a wire.


Question2: Electromagnetic induction is a phenomenon …….

  1. the procedure for charging a corpse.
  2. the process of producing a magnetic field as a result of a current flowing through a coil.
  3. inducing current in a coil as a result of relative motion between a magnet and the coil.
  4. the process of turning an electric motor's coil.


Question 3: A ______ is a device that generates an electric current.

  1. Generator
  2. Galvanometer
  3. Ammeter
  4. Engine


Question 4: The primary distinction between an AC generator and a DC generator is that

  1. An electromagnet is used in an AC generator, while a permanent magnet is used in a DC generator.
  2. A greater voltage will be produced by a DC generator.
  3. An AC generator will provide a greater voltage.
  4. The AC generator employs slip rings, while the DC generator employs a commutator.


Question 5: The current in the circuit during a short circuit …………

  1. significantly decreases
  2. remains unchanged
  3. significantly increases
  4. fluctuates indefinitely

 

Question 6: Which of the following assertions is True or False?

  1. An electric motor is a device that transforms mechanical energy into electrical energy.
  2. An electric generator operates on the electromagnetic induction principle.
  3. Parallel straight lines will form the field in the centre of a large circular coil carrying current.
  4. The live wire of an electric supply is commonly a wire with green insulation.

Question 7: Name three magnetic field sources.

Question 8: What causes a solenoid to act as a magnet? Can you use a bar magnet to calculate the north and south poles of a current-carrying solenoid? Explain.

Question 9: When is the force felt by a current-carrying conductor in a magnetic field the highest?

Question 10: Describe some of the gadgets that employ electric motors.

Question 11: A galvanometer is attached to a coil of an insulated copper wire. What happens if a bar magnet is (t) pushed into the coil, (ii) removed from inside the coil, and (iii) maintained stationary within the coil?

Question 12: A and B are two circular coils that are put next to each other. Will some current be generated in coil B if the current in coil A is changed? Give an explanation.

Question 13: State the rule for determining the direction of a: (i) magnetic field produced around a current-carrying straight conductor, (ii) force experienced by a current-carrying straight conductor placed in a magnetic field perpendicular to it, and (iii) current induced in a coil due to its rotation in a magnetic field.

Question 14: What causes an electric short circuit?

Question 15: What is the purpose of an earth wire? What is the purpose of earthing metallic appliances?

 

Answers:

Answer 1: (iv) The field is made up of concentric circles that are centred on the wire.

Answer 2: (iii) Inducing current in a coil as a result of relative motion between a magnet and the coil.

Answer 3: (i) generator.

Answer 4: (iv) The AC generator employs slip rings, while the DC generator employs a commutator.

Answer 5: (iii) Significantly increases.

Answer 6: (i) false (ii) true (iii) true (iv) false

Answer 7: (i) Conductor for transporting current (ii) Electromagnets (iii) Permanent magnets

Answer 8:

A current-carrying solenoid's magnetic field is extremely similar to that of a bar magnet. The solenoid, like a bar magnet, has N-polarity on one end and S-polarity on the other. We bring the N-pole of the bar magnet towards one end of the solenoid to identify the north and south poles. If there is an attraction, one end of the solenoid will have the south polarity, and the other will have the north polarity. If there is repulsion, one end of the solenoid will have north polarity, and the other end will have south polarity since similar poles repel each other.

Answer 9: The force experienced by the conductor is highest when the current is carried in a direction perpendicular to the direction of the magnetic field.

Answer 10: Electric motors are found in appliances such as electric fans, washing machines, mixers, grinders, blenders, laptops, MP3 players, and so on.

Answer 11:

(i) When a bar magnet is put into the coil, a temporary deflection in the galvanometer is detected, indicating the generation of a momentary current in the coil.

(ii) When the bar magnet is removed from the coil, the galvanometer deflects in the opposite direction, indicating the formation of an opposing current.

(iii) There is no deflection in the galvanometer while the bar magnet is kept stationary within the coil, indicating that no current is created in the coil.

Answer 12: Yes, there will be some current generated in coil B. Some current is generated in coil B when the current in coil A is altered. The magnetic field lines connected with coil A and coil B vary as the current in coil A changes. This causes induced current to flow via coil B.

Answer 13: (i) Right-hand thumb rule: If the current-carrying conductor is held in the right hand with the thumb pointing in the direction of the current, the direction of the magnetic field will be given by the curl of the fingers.

(ii) Fleming's left hand rule: Electric Current's Magnetic Effects Stretch the left hand's forefinger, middle finger, and thumb perpendicular to each other. If the forefinger points in the direction of the magnetic field, the middle finger points in the direction of the current, and the thumb points in the direction of a force in the conductor, the thumb points in the direction of a force in the conductor.

(iii) Fleming's right-hand rule: Stretch the right hand's thumb, forefinger, and middle finger perpendicular to each other. If the forefinger points in the direction of the magnetic field, the thumb in the direction of the conductor's velocity, and the middle finger in the direction of the current created in the conductor.

Answer 14: A short-circuit happens in a home circuit when the live and neutral wires come into direct contact with each other with no resistance. The circuit's resistance falls to zero, and excessive current begins to flow through it.

Answer 15: An earth wire is a safety precaution that offers a low resistance conducting channel for electricity. Due to excessive heat or wear and tear, the live wire may come into direct contact with the metallic cover of the appliances, resulting in an electric shock if touched. To avoid shock, the metallic section is linked to the earth through a three-pin connection, which allows electricity to pass to the earth in the case of a short circuit. Earthing metallic appliances are required because it assures that if there is any current leakage in the metallic cover, the potential of the appliance equals that of the earth. The earth's potential is nothing. As a consequence, the person handling the equipment will not be harmed by electricity.

From this chapter, we learned that when an electric current is passed through a coil coiled around an iron piece, the iron piece becomes magnetic. The electromagnet's strength is determined by the number of wires that turn around the core as well as the total current flowing through it. The magnetic impact increases with the increase of turns.

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