effect of electric current
Why does a compass needle get deflected when brought near a
A needle of a compass is also a magnet. It is a fact that, like
poles of two magnets repels each other and unlike poles attract. Due to this
repulsion and attraction between the poles, a magnetic needle deflects when
brought near a bar magnet.
magnetic field lines around a bar magnet.
List the properties of magnetic lines of force.
The properties of magnetic lines of force are as follows:
lines are closed curves emerging from the north pole and merging at the south
direction of field lines inside the magnet is from the south pole to the north
The field lines are
dense near a magnet and their density decreases as we move away from the
The field lines are
most intense near the poles, thereby indicating that the magnetic force is strongest
near the poles.
Any two field lines never
intersect each other. This means that no point in the magnetic field will ever
have more than one direction.
Why don't two magnetic lines of force intersect each other?
Magnetic lines of forces represent the direction of the
magnetic field. If two magnetic field lines intersect each other, it would mean
there are two directions of the magnetic field at a same point, which is impossible.
Thus, magnetic field lines never intersect each other.
Consider a circular loop of wire lying in the plane of the
table. Let the current pass through the loop clockwise. Apply the right-hand
rule to find out the direction of the magnetic field inside and outside the
For the current (I)
flowing inside a wire, the direction of the magnetic field (B) is shown the
diagram. The direction of the magnetic field when the current passes through a
circular loop is shown in the diagram below.
The direction of the magnetic field inside the loop appears
as if the magnetic fields pierce through the table. Whereas, the direction of the
magnetic field outside the loop appears as if the magnetic fields have emerged
out of the table.
The magnetic field in a given region is uniform. Draw a
diagram to represent it.
magnetic field lines inside a current-carrying solenoid are uniform.
Choose the correct option.
magnetic field inside a long straight solenoid-carrying current
(b) decreases as we move towards its end
(c) increases as we move towards its end
(d) is the same at all points
of the following property of a proton can change while it moves freely in a
magnetic field? (There may be more than one correct answer.)
In activity displayed below, how do we think
the displacement of rod AB will be affected if
(i) Current in rod AB is increased;
(ii) A stronger horse-shoe magnet is used; and
(iii) length of the rod AB is increased?
(i) If the current in the rod is increased, the magnetic
force exerted on the conductor and the deflection of the rod will increase.
If a stronger horse-shoe magnet is used, the
magnetic force exerted on the conductor and the deflection of the rod will
If the length of the rod AB is increased, there is no effect on the
displacement of the rod.
positively-charged particle (alpha-particle) projected towards west is
deflected towards north by a magnetic field. The direction of magnetic field is
(a) Towards south
(b) Towards east
Fleming's left-hand rule.
Fleming's left hand rule: If we arrange the thumb, the forefinger,
and the middle finger of the left hand at right angles to each other, then the
thumb points towards the direction of the magnetic force, the middle finger
gives the direction of the current, and the forefinger points in the direction
of the magnetic field.
What is the principle of an electric motor?
The principle of an electric motor is based on the magnetic
effect of electric current. A motor works on the principle that when a current-carrying
rectangular coil is placed in a magnetic field; it experiences a force and
rotates. The direction of rotation of the loop is given by the Fleming’s
What is the role of the split ring in an electric motor?
split-ring commutator in the electric motor reverses the direction of current
flowing through the coil after every half rotation of the coil. This makes the
coil rotate in the same direction continuously.
different ways to induce current in a coil.
current is produced in a coil which is placed in a region where the magnetic
field changes with time. The magnetic field can be changed when either the coil
is rotated in the magnetic field or the magnet is rotated around a static coil.
the principle of an electric generator.
generator works on the principle that when a straight conductor is moved in a
magnetic field, then current is induced in the conductor.
some sources of direct current.
sources of direct current are:
DC generator, etc.
sources produce alternating current?
sources producing alternating current are:
Power plants, etc.
Choose the correct option.
rectangular coil of copper wires is rotated in a magnetic field. The direction
of the induced current changes once in each:
(b) One revolution
(c) Half revolution
(d) One-fourth revolution
two safety measures commonly used in electric circuits and appliances.
Proper earthling of
all electric circuits
electric oven of 2 kW is operated in a domestic electric circuit (220 V) that has a current rating of 5 A.
What result do you expect? Explain.
current drawn by the electric oven can be obtained by the expression
the power of the oven, and the voltage supplied,
Since, the current drawn by the electric oven (9.09 A) exceeds the safe limit
of the circuit (5A), the fuse element of the electric fuse will melt and break
precaution should be taken to avoid the overloading of domestic electric
Some of the precautions that can be taken to avoid the
overloading of domestic circuits are as follows:
fuse in the circuit
using faulty appliances in the circuit
connecting too many appliances to a single socket
using too many heavy appliances at the same time