Magnetic Effects Of Electric Current

Earth wire is used as a safety precaution because whenever there is short circuit and if we touch that appliance we will get shock, so in spite of letting the current pass from our body, we make it pass to earth. Earth wire is in green/blue colour. It prevents overloading of live wire.

Uses of electromagnet are:–

I. It is used in motors and generators to change the magnetic flux linked with the coil and produce current.

II. It is used in transformers to alter the voltage by the phenomena of mutual induction.

We use an iron nail, battery, copper wire to make the circuit.

Different shapes of conductors have different type of magnetic field.

•Take a straight thick copper wire and place it between the points X and Y in an electric circuit. The wire XY is kept perpendicular to the plane of the paper.

• Horizontally place a small compass near this copper wire. See the position of its needle.

• Pass the current through the circuit by inserting the key into the plug.

• Observe the change in the position of the compass needle and the direction of deflection.

•Interchange the battery connection in the circuit so that the direction of the current in the copper wire changes.

• Observe the change in the direction of deflection of the needle.

Iron is the material used for making electromagnets because of its magnetic properties which makes it magnetize easily and makes it able to be magnetized for longer time.

An electromagnet is made by rounding a wire and make its shape as same as solenoid which acts as a bar magnet when electric current is passed through it. If we insert soft iron core in it, its magnetic field would increase.

• Take a small compass and a bar magnet.

• Place the magnet on a sheet of white paper fixed on a drawing board, using some adhesive material.

• Mark the boundary of the magnet.

• The south pole of the needle points towards the north pole of the magnet.

The north pole of the compass is directed away from the north pole of the magnet.

• Mark the position of two ends of the needle.

• Now move the needle to a new position such that its south pole occupies the position previously occupied by its north pole.

• In this way, proceed step by step until you reach the south pole of the magnet.

• Join the points marked on the paper by a smooth curve. This curve represents a field line.

• These lines represent the magnetic field around the magnet. These are known as magnetic field lines.

• Observe the deflection of the compass needle as you move it along the field line. The deflection increases as the needle is moved towards the pole.

a) The main function of earth wire is to absorb excess electricity passing through the appliance and to prevent overloading of live wire. The metallic appliances are earthed because whenever there is leakage of current, the leaked current passes through the earth wire to earth.

b) Short Circuit – When live wire comes in contact with Neutral wire then the resistance becomes zero and with Ohm's law current becomes infinite.

Overloading – When a large number of home appliances are connected simultaneously to same socket and they withdraw large amount of current than mentioned on the switch.

c) Fuse wire is a safety measurement used in case of overloading, short-circuiting or high voltage from the electricity board.

i. The usual capacity of the fuse wire in the line to feed lights and fans is around 15-20 A or less.

ii. The usual capacity of the fuse wire in the line to feed appliances of 2 kW or more power is a minimum of 30 A but it is preferred to have 50-60 A or less.

i. The deflection in the galvanometer occurs because of change in magnetic flux linked with the coil which results in formation of induced emf and further induced current due to the phenomena called electromagnetic induction.

ii. The direction of current appears to be anti-clockwise from point A because at point A there is formation of North pole and at point B there is formation of South pole.

iii. When the coil is moved away from north pole the direction of induced current gets reversed because point A now becomes South pole and point B now becomes North pole due to change in magnetic flux linked with the coil. So the galvanometer will show deflection to the left side.

iv. There would be no observation change in galvanometer as the magnet and closed coil are moving with same speed and have no relative motion. For formation of induced emf, there must be relative motion between magnet and coil.

i. Point P is the South pole and point Q is the North pole because of the specified direction of the current flowing in the solenoid and by using right-hand thumb rule our thumb points towards point Q, so it is North pole.

ii. Yes, magnetic field lines form closed loops and inside the solenoid they go from south to north pole and outside the solenoid it goes from north to south pole.

iii. By looking at the formula for magnetic field of solenoid we can say the two methods for increasing magnetic field are:–

B = μ_on I

a) By increasing the number of turns per unit length.

b) By increasing the amount of current passing through it.

a) Magnetic field is the area in which the magnetic strength of a magnet can be felt by a magnetic material, inside this field the magnet can either attract or repel the magnetic substances.

b) We can determine magnetic field direction by using magnetic compass by placing it at that point and observing the needle’s direction.

c) •Take a straight thick copper wire and place it between the points X and Y in an electric circuit. The wire XY is kept perpendicular to the plane of the paper.

• Horizontally place a small compass near this copper wire. See the position of its needle.

• Pass the current through the circuit by inserting the key into the plug.

• Observe the change in the position of the compass needle and the

direction of deflection.

•Interchange the battery connection in the circuit so that the direction of the current in the copper wire changes.

• Observe the change in the direction of deflection of the needle.

d) The direction of magnetic field depends upon the direction of current passing through that circular loop. If the current is flowing clockwise then the direction of magnetic field is inside the loop along the axis and vice versa.

Whenever current is passed through a conductor it develops magnetic field around it, in case of wire the magnetic field is circular around it and is given by right-hand thumb rule.

This is a rule you need to memorize that the magnetic field of all the instruments used is directly proportional to the number of turns with same powers.

That is, B – magnetic field ; N – number of turns.

The induced potential difference depends upon the number of turns and the rate of change of magnetic flux with time. The induced current depends upon the resistance of the coil.

The transfer of energy is in the form of radiation and radiation is in the form of electromagnetic rays and these rays do not need any material medium to propagate.

Iron can be magnetized easily and hence when it is introduced in the solenoid it gives its own magnetic field like solenoid and it is just like a wire passing through the solenoid through which current passes and it develops magnetic field around it.

An ideal solenoid acts like a wire but it is round in shape and if we look at it’s each turn one at a time we will get the direction of magnetic field using right-hand thumb rule. Each circle has magnetic field passing along its axis when we look inside it.

As we know that soft iron gets magnetized easily and it can retain its magnetization for a longer time, that is why it is used in electromagnets.

Fleming’s right hand rule is used in generators where the direction of induced current is found and Fleming’s left hand rule is used to find the direction of force acting on a current carrying conductor in a magnetic field.

In transformers, the current is passed from one coil(solenoid) to another solenoid through the phenomena of electromagnetic induction or more precisely called mutual induction.

From one current carrying coil, the other induces emf due to change in magnetic flux linked with it.

The general formula of magnetic field consists of the circumference of the body through which the magnetic field is passing in the denominator and in the numerator it consists of current passing through the body and a proportionality constant.

B(2R) =_oI

The magnetic field of solenoid is directly proportional to the current passing and the number of turns and has a proportionality constant which depends on material of conductor, instead of area magnetic field depends upon the length of solenoid.

When there is relative motion between a magnet and a closed loop there is formation of induced emf due to change in magnetic flux linked with the coil. More the speed more the induced emf.

Generator uses the principle of electromagnetic induction to produce induce emf which further produces induced current. The generator has a rotating coil between two magnet poles.

True.

By right hand thumb rule we can determine the direction of current with respect to magnetic field and vice versa, and we have found that direction of current becomes opposite along with the direction of magnetic field.

False.

To find the direction of magnetic field around a current carrying conductor we use Right hand thumb rule, and we use Fleming’s left hand rule to find the direction of force on current carrying conductor in magnetic field.

True.

The pattern of magnetic field is like concentric circles around straight conductor according to right hand thumb rule or cork screw rule.

True.

The pattern of magnetic field is same in current carrying solenoid and bar magnet and with same magnetic poles.

True.

Inside the solenoid, the magnetic field lines are equally spaced and parallel and are inside circular curves of solenoid which provide uniformity.

True.

The formula for the magnetic field of solenoid and most of the electric appliances is directly proportional to current passing through it.

False.

Maxwell’s corkscrew rule or right hand thumb rule is used to find the direction of magnetic field when we are given with the direction of current and vice versa. In order to find force on a current carrying conductor we use Fleming’s left hand rule.

True.

The phenomena of electromagnetic induction produces induced emf whenever there is change in magnetic flux linked with a closed coil.

True.

The relative speed between the magnet and the closed loop is one of the factors on which the magnitude of induced emf produced depends.

False.

Electric motor is a device which is used to convert electrical energy into mechanical energy. Generator is a device used to convert mechanical energy to electrical energy.

False.

Fleming’s right hand rule is used in generators to find the direction of induced current. To find the direction of current we use right hand thumb rule.

True.

The coil which is rotated between two magnets cuts the magnetic field due to which there is a change in magnetic flux linked with the coil and hence phenomena of electromagnetic induction take place.

False.

The electric current which always flows in the same direction is called Direct current, and the electric current which changes its polarity after same intervals of time is called alternating current.

True.

Red colour wires are used for live wire; Black colour wires are used for neutral, and green/blue are used for earth wire.

True.

We want to switch on and off different appliances at different time and we want to give each appliance the same potential difference and we do not want our other appliances not to work if one gets broken or damaged.

True.

Rubber is a good insulator of electricity and if we wear rubber gloves and shoes current is not able to pass through our body and we do not feel shock. It is a safety precaution against electricity.

True.

Earthing of electrical appliances is a safety measure taken in case of happenings of short circuits because short circuit can make current flow through us when in contact, so earthing gives current a direction to flow to earth rather than to humans.

False.

Unlike magnetic poles attract each(North and South attract) other and like magnetic poles repel each(North repel North and South repel South) other.

False.

If we magnetize something from one side touching to a magnet from North pole, there is always generation of opposite pole on the touching side which is South pole and on the non-touching side there will be North pole again.

True.

If we put a current carrying wire in a magnetic field perpendicular to its length, then it neither gets attracted or repelled by that field and hence these concentric circles neither have a starting point nor an ending point and the compass points tangential to the circles at every point.

False.

An electric generator is a device used to convert mechanical energy, which is used to rotate the coil between magnets, into electrical energy which is obtained by the phenomena called electromagnetic induction.