Q.1 State the factors on which the magnetic field due to a current carrying conductor depends.
Ans. The magnetic field at a point due to a current carrying conductor depends on the current through the conductor & the distance of the point from conductor.
i) The magnitude of the magnetic field produced at a given point is directly proportional to the magnitude of the current passing through the conductor.
ii) The magnetic field produced by a given current in the conductor decreases as the distance from the conductor increases.
«Q. 2 State the right hand thumb rule.
Ans. Imagine you are holding a current carrying straight conductor in your right hand such that the thumb points towards the direction of current, then the curled fingers around the conductor will give the direction of the magnetic field.
Fig. Right hand thumb rule
Q.3 Describe with a neat labelled diagram, the pattern of magnetic field lines (magnetic lines of force) due to a current through a circular loop (coil). Also explain how the magnetic field depends on the number of turns (n) in the loop.
Fig – Showing Magnetic field lines (magnetic lines of force) due to a current through a circular loop (coil) of ‘n’ turns.
1. It is seen that every point of the loop forms a centre of a large number of concentric lines forming a series. The circles are small near the wire & becomes large as we move away from the wire. At the centre of the loop, the arcs of these circles appear as straight lines because of very large radius of the circle.
2. The magnetic field produced by a current carrying wire at a given point is directly proportional to the current through the wire. The loop (coil) has ‘n’ turns, the field produced is n timer that produced by a single turn, because the current in each turn has the same direction & the field due to each turn contributes equally to the total field.
«Q.4 Define solenoid.
Ans. A coil of many turns of insulated copper wire wrapped (wound) in the shape of cylinder is called as solenoid.
Q.5 What is a solenoid ? How will you use a solenoid ?
Ans. A solenoid is a coil of many turns of insulated copper wire wound around a cardboard cylinder, to form a cylindrical coil. When a current is passed through the wire, the solenoid acts like a magnet. The magnetic lines of force are very similar to the lines of force of a bar magnet. The magnetic field in the hollow of the solenoid is very strong. When a carbon steel rod is placed in the hollow of the solenoid, & current is switched on, the rod gets magnetised. Rods of materials like carbon-steel, tungsten steel, cobalt steel & chromium steel are used in the preparation of permanent magnets, if the magnetic field of solenoid is strong enough. These magnets are prepared by using the alloys like alnico & nipermag also.
Q.6 Draw a neat labelled diagram showing the magnetic lines of force (magnetic field lines) due to a current carrying solenoid.
Fig. – showing magnetic lines of force (magnetic field lines) due to a current carrying solenoid.
B – Battery K – Plug key I – Current N – North pole S- South pole
Q. 6. Distinguish between
a) Bar magnet & Solenoid
i. Bar magnet is solid, consist of soft iron or suitable alloy.
ii. Its magnetic field is weaker that that of solenoid.
iii. It does not require electric current to function as a magnet.
iv. It is a permanent magnet.
v. Its field has a fixed strength.
i. Solenoid is a hollow coil of an insulated wire of copper or aluminium.
ii. A solenoid can be designed to produce a field much stronger or much weaker than that of a bar magnet.
iii. It require electric current, without which it cannot function.
iv. It function as a temporary magnet.
v. It field can be varied by varying the current in it.
b) Bar magnet & Electromagnet
i. Bar magnet is a permanent magnet.
ii. It does not require electric current to act as a magnet.
iii. Its north pole & south poles are permanently fixed.
iv. The strength of its magnetic fields is fixed.
v. It does not produce any heat, on its own.
vi. It consists of a piece of iron or a suitable alloy in the shape of a bar.
i. Electromagnet is a temporary magnet. In the absence of current it does not work as a magnet.
ii. It requires electric current to act as a magnet.
iii. The position of its poles can be reversed by reversing the direction of current passing through it.
iv. The strength of its magnetic field can be varied by varying the current passing through it.
v. Electromagnet provides heat, as a part of electric energy is transformed into heat.
vi. It consists of an insulated wire wound in the form of a coil, usually wound on a piece of iron or a suitable alloys of various shapes bar, horse shoe, disc, etc.
Q. 7 Name the materials used to prepare permanent magnets.
Ans. Hard steel, carbon steel, chromium, steel, cobalt & tungsten steel, Alnico (Alloy of aluminium-nickel-cobalt), nipermag (alloy of iron, nickel, aluminium & titanium) are the material used for the preparation of permanent magnets.
Q. 8 Where permanent magnets are used ?
Ans. Permanent magnets are used in microphones, loudspeakers, electric clocks, ammeters, voltmeters & speedometers, etc.
Q. 9 Give scientific reasons.
«1. Alloys like alnico & nipermag are used in industries.
Ans. i) Many instruments like loudspeakers, a telephone earpiece, measuring instruments like an ammeter, powerful voltmeter, etc. require the use of permanent magnets.
ii) Originally carbon steel was used to prepare permanent magnets.
iii) Later research proved that addition of certain elements like nickel, chromium, cobalt, tungsten, etc improved the magnetic properties of permanent magnets.
iv) Alnico is an alloy of iron containing aluminium, nickel & cobalt. Nipermag is an alloy of iron containing nickel,aluminium & titanium. Therefore, permanent magnets prepared from these alloys are most suitable for use in industries.
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