Magnetic Field due to a Current through a Straight Conductor
Q) Describe an activity to determine the direction of magnetic field produced by a current
carrying straight conductor. Also show that the direction of the magnetic field is reversed on
reversing the direction of current.
Fix a cardboard and pass a straight wire through a hole in cardboard and connect the two ends
of the wire with a cell through a rheostat and key with a cell. Sprinkle iron filings uniformly on
the card board. Pass the current in the wire and gently tap the card board. You would find that
iron filings align themselves in concentric circles around the copper wire which represents the
magnetic field around the current carrying conductor. The direction of magnetic field changes on
reversing the direction of current.
Right-Hand Thumb Rule
If a current carrying conductor is imagined to be held in your right hand such that the thumb
points along the direction of current, then the direction of the wrapped fingers will give the
direction of magnetic field lines
Q -1) A current flows in a conductor from east to west. Find The direction of the magnetic field
at a points above the conductor ?
Magnetic Field due to a Current through a Circular Loop
Q) Describe in brief an activity to study the magnetic field lines due to a current carrying circular
oil.
In order to find the magnetic field due to a coil, it is held in a vertical plane and is made to pass
through a smooth cardboard in such a way that the centre (O) of the coil lies at the cardboard. A
current is passed through the coil and iron filings are sprinkled on the cardboard. These iron
filings arrange themselves in a pattern similar to one shown in the figure. This pattern represents
the magnetic field lines due to the coil.
Magnetic Field due to a Current in a Solenoid
A coil of many circular turns of insulated copper wire wrapped closely in the shape of a
cylinder is called a solenoid.
Difference between bar magnet and solenoid
Q) What are the similarities between a current-carrying solenoid and a bar magnet?
1) The magnetic field lines due to current carrying solenoid are identical to those of bar magnet.
Thus a current carrying solenoid behaves just like a bar magnet with fixed polarities at the ends.
The end at which the direction of current is clockwise behaves like a south pole and the end at
which current is anti clockwise behaves like a north pole.
2) A current-carrying solenoid when suspended freely, will set itself in the north south direction
exactly in the same manner as a bar magnet does.
3) A current-carrying solenoid also acquires the- attractive property of magnet. If iron filings are
brought near the solenoid, it attracts them when current flows through the solenoid.
Q-2) . (a) What is an electromagnet? List any two uses.
(b) Draw a labelled diagram to show how an electromagnet is made.
(c) State the purpose of soft iron core used in making an electromagnet.
(d) List two ways of increasing the strength of an electromagnet if the material of the
electromagnet is fixed
FORCE ON A CURRENT CARRYING CONDUCTOR IN A MAGNETIC FIELD
Q) . Describe an activity with labelled diagram to show that a force acts on current carrying
conductor placed in a magnetic field and its direction of current through conductor. Name the
rule which determines the direction of this force.
Ans: A small aluminium rod suspended horizontally from a stand using two connecting wires.
Place a strong horseshoe magnet in such a way that the rod lies between the two poles with the
magnetic field directed upwards. For this, put the north pole of the magnet vertically below and
south pole vertically above the aluminium rod.
Connect the aluminium rod in series with a battery, a key and a rheostat. Pass a current through
the aluminium rod from one end to other (B to A). The rod is displaced towards left. When the
direction of current flowing through the rod is reversed, the displacement of rod will be towards
right. Direction of force on a current carrying conductor is determined by Fleming’s left hand
rule.
Q) ) State the rule which helps, in finding the direction of magnetic force on conductor.
Fleming’s left hand rule is as follows: Stretch out the thumb, the forefinger, and the second
(middle) finger of the left hand so that these are at right angles to each other. If the
forefinger gives the direction of the magnetic field (N to S), the second (middle) finger the
direction of current then the thumb gives the direction of the force acting on the conductor
Q) . State the direction of magnetic field in the following case.
Q.A current carrying conductor is placed in a magnetic field. Now answer the following.
(i) List the factors on which the magnitude of force experienced by conductor depends.
(ii) When is the magnitude of this force maximum?
(iii) State the rule which helps, in finding the direction of motion of conductor.
(iv) If initially this force was acting from right to left, how will the direction of force
change if:
(a) direction of magnetic field is reversed?
(b) direction of current is reversed?
Q. State whether an alpha particle will experience any force in a magnetic field if (alpha particles
are positively charged particles)
(i) it is placed in the field at rest.
(ii) it moves in the magnetic field parallel to field lines.
(iii) it moves in the magnetic field perpendicular to field lines. Justify your answer in each cas
Q. An electron enters a magnetic field at right angles to it, as shown in The direction of force
acting on the electron will be
a)to the right. (b) to the left. (c) out of the page. (d) into the page.
Q. An electron beam is moving vertically upwards. If it passes through a magnetic field which is
directed from South to north in a horizontal plane, then in which direction will the beam deflect?
