Magnetic Effects Of Electric Current

The SI unit of magnetic field is Tesla denoted by T.

1 T is defined as the magnetic field in which particle of charge 1 Coulomb moving perpendicularly to a magnetic field at a speed of 1 m/s experiences the force of 1N.

The Magnetic field lines always begin from the North ‘N’ pole of the magnet and ends on south ‘S’ pole of the magnet.

However inside the magnet the direction of magnetic field lines is from ‘S’ pole to ‘N’ pole.

The figure below illustrates the magnetic field lines direction inside the bar magnet.

The two magnetic field lines never intersect each other because if they intersect than two tangents can be drawn from the point of intersection of the field lines which will give the two directions of the field from the same point (shown in figure below) which is impossible because the resultant force on a pole (north/south) at any point can only be in one direction. Hence the field lines never intersect.

Following are the ways by which we can determine the magnetic field in a space.

1. Magnetic field can be written in terms of vector potential an by determining the potential we can find the strength.

2. By using the magnetometer we can measure the strength of the magnetic field. Figure below shows the magnetometer.

(i) Stronger = the magnetic field lines are stronger in the region around the wire and it decreases with the increase in the distance from the wire.

(ii) Weaker = the magnetic field lines are weaker in the region far away from the wire because as the distance from the wire increases the magnetic field intensity decreases.

Figure below shows the field lines due to wire.

The magnetic field is directly proportional to the number of turns in the magnet. Therefore on increasing the number of turns the magnetic field will increase because, with addition of each turn there will be an increase in number of charge carriers that contribute to the field at a point.

When current is passed through a solenoid, the magnetic fields act almost like that of a bar magnet. One end acts as the magnetic north pole, and the other end acts as the magnetic South Pole.

The magnetic curves inside the solenoid are in parallel straight lines, which indicate that the magnetic field is same at all points inside the solenoid. However, the field lines outside the solenoid travels from one pole to the other. Figure below shows the magnetic field lines inside the solenoid

the direction of the current in the circular current carrying coil is given by the Thumb rule.

Direction of magnetic field at centre for the loop carrying current in clockwise direction is perpendicular to the plane and is inward (going into the plane) which is south pole shown in the figure below.

For the point outside the surface of the loop the direction is outwards (going outside of the plane).

An electromagnet is a device used to generate a magnetic field with the help of an electric current.

Under the influence of electric current, all atoms are reoriented to start pointing in the same direction. All these individual magnetic fields together create a strong magnetic field. As the current flow increases, this degree of reorientation also increases, resulting in a stronger magnetic field.

Once all the particles are reoriented perfectly in the same direction, increasing current flow will not affect the magnetic field produced. At this point, the magnet is said to be saturated.

(i) Maximum: When the direction of current is perpendicular to the direction of the magnetic field the force on wire is maximum.

(ii) Minimum: When the direction of current is parallel to the direction of the magnetic field the force on wire is minimum.

Fleming’s Left hand rule gives the direction of force on a current carrying conductor placed perpendicular to the magnetic field.

Fleming’s Left hand rule: According to this rule, stretch the thumb, fore-finger and middle finger of left hand such that they are mutually perpendicular. If the middle finger points in the direction of the magnetic field, the fore-finger points in the direction of flow of current, then the thumb points in the direction of motion i.e., force acting on the conductor.

Figure below illustrates it.

By the right hand rule the thumb pointing in the direction of the current and the forefingers pointing in the direction of the magnetic field, than perpendicular to the palm is the direction of the force on the conductor. Therefore the direction of the force on the conductor is south west.

The human body magnetism comes from two sources one is magnetism from earth and other is the metabolism within the cells in the body.

In human body small electric current travel along the nerve cells due to ions, same way as electricity flows through the wire. This current produces very weak magnetic field in the human body. Heart and Brain are the two main organs in the human body where this field is significant.

Electric motor is the device in which electrical energy is converted into the mechanical energy.

It works on the principle that when a rectangular coil is placed in a magnetic field and current is passed through it. A force acts on the coil which rotates it continuously. Figure below shows the electric motor

Electromagnetic Induction is a current produced because of voltage production (electromotive force) due to a changing magnetic field. This either happens when a conductor is placed in a moving magnetic field (when using AC power source) or when a conductor is constantly moving in a stationary magnetic field.

This phenomenon was discovered by Michael Faraday. Figure below shows the setup for electromagnetic induction.

It can be used to determine the direction of current in a generator's windings. It can also be used to show the direction of induced current when a conductor attached to a circuit moves in a magnetic field.

Fleming right hand rule is mainly applicable for the electric generator. Figure below shows how to determine the direction of current using Fleming right hand rule.

Electric generator is the device which converts the mechanical energy into the electrical energy.

It works on the Faraday’s law of the Electromagnetic Induction which says that whenever a conductor is placed in a varying magnetic field, EMF is induced and this induced EMF is equal to the rate of change of flux.

Electric generators are of two types A.C generator and D.C generator. Figure below shows the A.C generator.

in our country the potential difference is 220 V and the frequency is 50 Hz. It is different for the different countries. And the potential difference is between the live wire and the neutral wire.

Electrical wires follow standard color coding that helps classify each wire function in the circuit. In India wires are RGB mode i.e. Red- Green- Black. Each of these RGB wire have different functions.

1. RED = Red wire signifies the phase in electric circuit. It is the live wire which cannot be connected to another red wire or black wire.

2. BLACK = Black wires signifies neutral wire in electric circuit. The neutral wire is connected to neutral bus bar inside an electric panel.

3. GREEN = Green wire stands for grounding/ Earthing in electric circuit. A green wire should be on can be connected to green wire only (no other wire).

Fuse is used for protecting appliances due to short-circuiting or overloading. The fuse is rated for a certain maximum current and blows off when a current more than the rated value flows through it.

If a fuse is replaced by one with larger ratings, the appliances may get damaged while the protecting fuse does not burn off. This practice of using fuse of improper rating should always be avoided.

A short circuit is an electrical circuit that allows a current to travel along an unintended path with no or a very low resistance. This results in an excessive amount of current flowing into the circuit

A common type of short circuit occurs when the positive and negative terminals of a battery are connected with a low-resistance conductor, like a wire. With a low resistance in the connection, a high current will flow, causing the delivery of a large amount of energy in a short period of time

The current in a circuit depends on the rating of the appliances connected to it. The choice of wires depends upon the maximum current estimated to pass through them. If the total power rating of the appliances exceeds this permitted limit, they tend to draw a large current. This is known as overloading due to excessive heating takes place.

Overloading occurs when too many appliances are connected in a single socket or live and neutral wires come in contact with each other.

A fuse is an electrical safety device that is used to cut electrical supply during short circuit. It is a metal wire or strip that melts when too much current flows through it, thereby interrupting the current.

Figure below shows the fuse.

In order to prevent us from getting electric shock we have to connect all wires to the earth wires, and lights operate in live wire. Also we have to connect neutral wire to complete the circuit.

By using the clock face rule which states that "When an observer, looking at the face of the coil, finds the current to be flowing in the anti-clockwise direction, then the face of the coil will behave like the North Pole. While if the current is in the clockwise direction, the face of the coil will behave like South Pole.

South Pole: A

North Pole: B

Alternating current can be transmitted over the long distances without the loss of energy. Also alternating voltage can be stepped up and stepped down using transformer.

When the magnet AB is broken into pieces as shown in the figure below.

Polarity of A and C is north

Polarity of B and D is south

Because single poles of magnet do not exist when the magnet is broken the two poles (north and south) are created immediately.

The direction of current is from left to right as the electron beam enters from left to right and the magnetic field is into the page.

According to the Fleming’s left hand rule the force is perpendicular to the flow of current and is in its left side. So electron beam deflects towards bottom of the page. As shown in the figure below.

(i) According to the Lenz’s Law induced emf will oppose the source of the charge, thus to oppose the approaching South Pole magnetic South Pole will be developed at the end of the magnet. Thus the current will flow in the clockwise direction as shown in the figure below.

(ii) According to the Lenz’s Law induced emf will oppose the source of the charge, thus to oppose the going away South Pole magnetic North Pole will be developed at the end of the magnet so that the south pole of the magnet do not go away. Thus the current will flow in the anticlockwise direction as shown in the figure below.

(i) The bulb lights due to the mutual induction. The emf is produced in the conductor when the magnetic flux linked with the conductor changes. Due to this emf the bulb gets lighted.

(ii) When the coil P is move upwards the magnetic flux linked with the coil gets decreased due to which the induced emf gets decreased, hence the bulb gets dimmer.

(i) A is North Pole and B is South Pole because magnetic field lines originate from North Pole and ends at South Pole.

(ii) C and D are South Pole because the magnetic field lines end at the South Pole and same type of poles repel each other.

(iii) E and F are South Pole because the magnetic field lines end at the South Pole and same type of poles repel each other.

A magnetic compass needle pointing North and South shows deflection when a bar magnet or a current carrying loop is brought near it. This happens because the magnetic fields of the compass needle and the bar magnet (or current carrying loop) interact with each other.

Salient features of magnetic field lines:-

a. Magnetic field lines follow the direction from the North Pole to the South Pole.

b. Magnetic field lines always show concentric pattern.

c. Magnetic field lines do not cross one another.

d. Closer the field lines; stronger is the magnetic field and vice-versa is also true.

e. Magnetic field lines are closer near the poles; which shows greater strength of magnetic field near the poles.

The magnetic field lines around a straight conductor (straight wire) carrying current are concentric circles whose centers lie on the wire. Figure below shows the field lines.

Right hand thumb rule states that if a current carrying straight conductor is supposedly held in the right hand with the thumb pointing towards the direction of current, then the fingers will wrap around the conductor in the direction of the field lines of the magnetic field.

(i) The current in first case is the Direct current because it is constant with the time. The current in second case is the Alternating current because its direction and magnitude changes continuously with the time.

(ii) Source of direct current are solar cell, fuel cell etc.

Source of alternating current the electricity coming to our home.

(iii) The frequency of the Alternating current in India is 50 Hz.

(iv)

(i) Following are the errors in the circuit given above.

a) Fuse is incorrectly connected to the Neutral wire (N) it must be connected to the live wire (L).

b) Bulb B₂ is not connected to the neutral wire.

(ii) Element of electric heater has high melting point in order to stand high temperatures while element of fuse has low melting point.

(iii) 1. Each appliance will have and equal potential difference.

2. Each appliance will have a separate switch to ON/OFF the flow of the current.

(i) Overloading can lead to damage, poor performance and possible failure. There may be a risk of fire or damage to components. It can also lead to sparks, arcs or insulation failure. Current overload will cause things to heat up, and then possibly melt, set of fire, damage insulation or cause components to fail. Some components will be damaged by the excessive current without overheating

(ii) Amit is very caring and worried towards his society and people. He is also quite ware and intelligent. He uses his knowledge of science for helping society which is the sole purpose of education.

(i) Rajat has purchased a Compass because it contains the magnet and in presence of the electric current the needle in it deflects which helps in detecting the current carrying wires. Figure below shows the compass.

(ii) Rajat noticed the deflection in the needle of the compass when he was moving the device slowly over the wires. Actually due to interaction between the magnetic field of the compass and of the current carrying wires the deflection is produced.

(iii) Rajat is very aware and clever. He quickly brought the instrument to help his aunt this shows he is very helping and caring towards his aunt.

In option A the magnetic field lines are circular; also they start and end at definite point.

But in option D the magnetic field lines are shown as square in shape therefore it is incorrect. In option B and C they are not starting and ending at definite point.

Since the key is taken out due to which there is no magnetic field due to wire. Hence only magnetic field of earth is present and the magnetic field lines of the earth are straight lines parallel to each other.

Since the magnetic field outside the solenoid is zero because it gets cancelled due to the each circular ring. Hence no compasses will get deflected.

Initially the ship is at 8° south of west. Declining 18⁰ from 8⁰ south of west results in actual direction. Now from north we get the direction of 90-18-8 = 90-26 = 64° West of North.

For the loop, using Lenz’s Law, the force on the part which is nearer, due to the current in the long wire is attraction and force on the part which is farther is repulsion.

F (attraction) > F (repulsion)

Hence loop moves towards the wire

The core of solenoid must be of some soft type magnetic material which can be strongly magnetized but does not retain induced magnetism.

The force on the wire due to the interaction of magnetic fields of the bar magnet and current carrying wire can act only in upwards or downwards direction.