Q.1What is meant by solenoid? How does a current carrying solenoid behave? Give its main use.
Answer. Solenoid: A coil of many circular turns of insulated copper wire wound on a cylindrical insulating body (i.e., cardboard etc.) such that its length is greater than its diameter is called solenoid.

When current is flowing through the solenoid, the magnetic field line pattern resembles exactly with those of a bar magnet with the fixed polarity,
i.e. North and South pole at its ends and it acquires the directive and attractive properties similar to bar magnet. Hence, the current carrying solenoid behave as a bar magnet.
Use of current carrying solenoid: It is used to form a temporary magnet called electromagnet as well as permanent magnet.

Q.2 Why and when does a current carrying conductor kept in a magnetic field experience force? List the factors on which direction of this force depends?
Answer. The drifting of free electrons of a conductor in a definite direction causes the current to flow through it. When such conductor is placed in a uniform magnetic field, each drifted electron of a conductor experience a magnetic force. This force is collectively experience by a conductor as a whole. Hence a current carrying conductor kept in a magnetic field experience a force. The direction of magnetic force depends on
(i) direction of current through the conductor, and
(ii) direction of magnetic field.

Q.3 How is the strength of magnetic field near a straight current-conductor
(i) related to the strength of current in the conductor?
(ii) is affected by changing the direction of flow of current in the conductor?
Answer.
(i) The strength of magnetic field around a straight current conductor increases
on increasing the strength of current in the conductor or vice versa.
(ii)The direction of magnetic field around a straight current carrying conductor gets reversed if the direction of current through that conductor is reversed.

Q.4 Explain any two situations that can cause electrical hazards in domestic circuits.
Answer. (i) Connecting too many electrical devices to a single socket or in the extension
cord for any length of time draws high current from the mains that will exceed the current rating of connecting wires. The wires cannot withstand such a high current and melt and may cause fire.
(ii) Most electrical hazards in domestic circuits are caused by the faulty electrical outlets, old and out-dated appliances. The chances of short circuit i.e., contact of live wire and neutral wires with each other due to damage in their insulation or some fault in the appliances are very high. It may result spark at the contact point which may even cause fire,

Q.5 List in tabular form two major differences between an electric motor and a
generator.
Answer.

Q.6 Write one application of each of the following:
(a) Right-hand thumb rule (b) Fleming’s left hand rule
(c) Fleming’s right hand rule
Answer.
(a) Right-hand thumb rule is used to find the direction of magnetic field in a coil of wire and the electric current in a straight conductor.
(b) Fleming’s left hand rule is used to find the direction of force exerted on a current-carrying conductor placed in a magnetic field as in electric motor.
(c) Fleming’s right hand rule is used to find the direction of induced current in a closed circuit placed in changing magnetic field as in electric generator.

Q.7 Consider a circular loop of wire lying in the plane of the paper. Let the current
pass through the loop clockwise. With the help of a diagram, explain how the direction of the magnetic field can be determined inside and outside the loop. Name the law used to find the direction of magnetic field.
Answer. Consider a circular loop of wire of radius r with centre O lying in the plane of the paper. Let the current i pass through the loop clockwise. According to right hand thumb rule, direction of magnetic field due to any portion of small current carrying length of the coil is:
Direction of magnetic field inside the loop — Perpendicular to the plane of paper inwards.
Direction of magnetic field outside the loop — Perpendicular to the plane of paper outwards.

So, the direction of magnetic field can be considered as the direction of total magnetic field due to circular coil as current through all the elements will contribute to the magnetic field in the same direction.

Q. 8 A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (a) pushed into the coil,
(b) withdrawn from inside the coil,
(c) held stationary inside the coil?
Answer.
(a) When a bar magnet is pushed into the coil, magnetic field lines linked with
the coil changes (increases). It causes the electric current to get induced in it. The needle of galvanometer will move momentarily in one direction.
(b) When a bar magnet is withdrawn from inside the coil, the magnetic field lines linked with the coil changes but in decreasing order. Current will be induced in the coil which will be indicated by deflection of needle in the galvanometer. The deflection is opposite to that in case (a). This indicates that the direction of induced current is now opposite to the direction of induced current in case (a).
(c) When bar magnet is held stationary inside the coil, there is no deflection in the galvanometer. This is because there is no change in magnetic field lines linked with the coil. Hence, no induced current will flow through the coil.

Q.9 (a) Two magnets are lying side by side as shown below.
Draw magnetic field line between poles P and Q.

(b) What does the degree of closeness of magnetic field lines near the poles signify?
Answer.

(b) The degree of closeness of magnetic field lines near the poles signify that the field is stronger there, i.e. the pole of another magnet when placed in the magnetic field experiences a greater force where the field lines are crowded.

Q.10 For the current carrying solenoid as shown below, draw magnetic field lines and giving reason explain that out of the three points A, B and C at which point the field strength is maximum and at which point it is minimum.

Answer. Outside the solenoid magnetic field is minimum. At the ends of solenoid, magnetic field strength is half to that inside it. So Minimum – at point B; Maximum – at point A

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