Magnetic Effects of Electric Current

Question 1

Magnet

Answer 1

A magnet is a material that produces a field that attracts or repels other such materials of magnetic nature.
Lodestone is a naturally occurring magnet. It attracts materials like Iron, Nickel, Cobalt etc.

Question 2

North and South Poles

Answer 2

A magnet is always bipolar with poles named north and south poles. These two poles always
exist together and can not be separated. North pole of a magnet is the side which points to
Earth’s geographic north when it is freely suspended.

Question 3

Like poles repel and unlike poles attract

Answer 3

Similar to charges, the poles attract and repel. Like poles repel while unlike poles attract
each other.

Question 4

Bar magnet

Answer 4

A bar magnet is a rectangular object, made up of iron, steel or any other ferromagnetic substance, that shows permanent magnetic properties. It has two poles, a north and a south pole such that when suspended freely, the north pole aligns itself towards the geographic
north pole of the Earth.

Question 5

Magnetic field

Answer 5

The region around a magnet where its magnetic influence can be experienced is called a
magnetic field. The direction and strength of a magnetic field are represented by magnetic
lines of force

Answer 6

Iron filings around a bar magnet show us the magnetic field lines that surround the bar
magnet. The magnetic field lines can be defined as imaginary lines that graphically
represents the magnetic field that is acting around any magnetic substance.

Question 7

Magnetic field lines

Answer 7

The magnetic field lines of a magnet form continuous closed loops.
The tangent to the field line at any point represents the direction of the net magnetic
field at that point.
The larger the number of field lines crossing per unit area, the stronger is the magnitude of the magnetic field.
Magnetic field lines do not intersect.

Question 8

Magnetic field lines for a closed loop

Answer 8

Since magnets have dipoles, magnetic field lines must originate and end. Therefore by
convention, it starts at the north pole and moves towards the south pole outside the bar
magnet and from south → north inside the magnet. Hence it forms closed loops.

Question 9

No two magnetic field lines intersect

Answer 9

Magnetic field lines do not intersect as there will be two tangential magnetic field
directions associated with the same point, which does not occur. If a compass needle is
placed at that point, it will show two different directions of the magnetic field which is
absurd.

Question 10

Relative strength of magnetic field inferred from magnetic field lines

Answer 10

The closer or denser the magnetic field lines, greater is the magnetic field’s strength.

Question 11

Magnetic Field Due to a Current Carrying Conductor
Oersted’s experiment

Answer 11

When electric current flows through a current carrying conductor, it produces a magnetic field around it. This can be seen with the help of a magnetic needle which shows deflection.
The more the current, the higher the deflection. If the direction of current is reversed, the direction of deflection is also reversed.

Question 12

Electromagnetism and electromagnet

Answer 12

An electromagnet is an artificial magnet which produces a magnetic field on the passage of
electric current through a conductor. This field disappears when the current is turned off.
The phenomenon of producing or inducing a magnetic field due to the passage of electric current is called as electromagnetism.

Question 13

Magnetic field due to a straight current carrying conductor

Answer 13

When current is passed through a straight current carrying conductor, a magnetic field is
produced around it. Using the iron filings, we can observe that they align themselves in
concentric circles around the conductor.

Question 14

Right-hand thumb rule

Answer 14

If a straight conductor is held in the right hand in such a way that the thumb points along the direction of the current, then the tips of the fingers or the curl of the fingers show the direction of magnetic field around it.

Question 15

Magnetic field due to current through a circular loop

Answer 15

The right-hand thumb rule can be used for a circular conducting wire as well as it
comprises of small straight segments. Every point on the wire carrying current gives rise to
a magnetic field that appears as straight lines at the centre

Question 16

Magnetic field due to current in a solenoid

Answer 16

A solenoid is a coil of many circular windings wrapped in the shape of a cylinder. When current is passed through it, it behaves similar to a bar magnet, producing a very similar
field pattern as that of a bar magnet. To increase the strength a soft iron core is used.

Question 17

Force on a Current Carrying Conductor in a Magnetic Field
Ampere’s experiment

Answer 17

When an electric conductor is placed in a magnetic field, it experiences a force. This force
is directly proportional to the current and is also perpendicular to its length and magnetic field

Question 18

Force on a straight current carrying conductor placed in a magnetic
field

Answer 18

Force on a straight current carrying conductor is mutually perpendicular to the magnetic
field and the direction of the current.

Question 19

Fleming’s left-hand rule

Answer 19

Fleming’s left hand rule states that the direction of force applied to a current carrying wire
is perpendicular to both, the direction of current as well as the magnetic field.

Question 20

Electric motor

Answer 20

Electric Motor converts electrical energy into mechanical energy.
Current enters arm AB through brush X and current flows through brush Y from C to D. Using Fleming’s LHR we find that the force pushes AB downwards and pushes CD
upwards.

In electric Motor the split rings PQ act as a commutator that reverses the direction of the current. The reversing of the current is repeated at each half rotation, giving rise
to a continuous rotation of the coil.

Question 21

Electromagnetic Induction and Electric Generators
Faraday’s experiment

Answer 21

Faraday discovered that a magnetic field interacts with an electric circuit by inducing a voltage known as EMF (electromotive force) by electromagnetic induction.
Moving a magnet towards a coil sets up a current in the coil circuit, as indicated by deflection in the galvanometer needle

Question 22

Electromagnetic induction

Answer 22

The phenomenon of electromagnetic induction is the production of induced EMF and
thereby current in a coil, due to the varying magnetic field with time. If a coil is placed near
to a current-carrying conductor, the magnetic field changes due to a change in I or due to
the relative motion between the coil and conductor. The direction of the induced current is
given by Fleming’s right-hand rule.

Question 23

Fleming’s right-hand rule

Answer 23

According to Fleming’s right-hand rule, the thumb, forefinger and middle finger of the right
hand are stretched to be perpendicular to each other as shown in the illustration, and if the
thumb represents the direction of the movement of conductor, fore-finger represents
direction of the magnetic field, then the middle finger represents direction of the induced
current

Question 24

Electric generator

Answer 24

*The device that converts mechanical energy into electrical energy.
*Operates on the principle of electromagnetic induction.
*AC Generation: The axle attached to the two rings is rotated so that the arms AB and CD move up and down respectively in the produced magnetic field. Thus the induced
current flows through ABCD
*After half rotation the direction of current in both arms changes. Again by applying Fleming’s right hand rule, the induced currents are established in these arms along
directions DC and BA, therefore the induced I flows through DCBA.
*DC Generation: They work just like AC, instead use half rings to produce current in
one direction only without variations in magnitude.

Question 25

Domestic Electric Circuits
Fuse

Answer 25

Fuse is a protective device in an electrical circuit in times of overloading.
Overloading is caused when the neutral and live wire come in contact due to damage to the insulation or a fault in the line.
In times of overloading the current in circuit increases (short circuit) and becomes hazardous. Joule’s heating(resistive or ohmic heating on the passage of current) in the
fuse device melts the circuit and breaks the flow of current in the circuit

Question 26

Domestic electric circuits

Answer 26

*Livewire has a voltage of 220 V and is covered with red insulation.
*Earth wire has a voltage of 0 V (same as Earth) and is covered with green insulation.
*The neutral wire has black insulation.
*In our houses, we receive AC electric power of 220 V with a frequency of 50 Hz.

Question 27

Power loss in transmission

Answer 27

Power losses in transmission lines over long distances occur due to Joule’s heating. This
heat (H) ∝ l
2R losses where R is the line resistance