Quick Revision for Class X Physics SA1


Q.1. Why is the tungsten metal more coiled in the bulb and not installed in straight parallel wire form?
Ans. The coiled wire of tungsten increases the surface area of the wire in very less space so as to emit more light and helps in glowing with more intensity.
Q.2. Why are fairy decorative lights always connected in parallel?
Ans. When the fairy lights are connected in series the resistance offered will be greater and brightness of the bulbs will be affected. But in parallel connection all the bulbs will glow with same intensity and if any more bulbs gets fused the other bulbs will continue to glow.
Q.3. What will happen when -a)      Voltmeter is connected in series?b)      Ammeter is connected in parallel?
Ans. a)      Negligible current will pass through the circuit because the voltmeter has a very high resistance.b)      Ammeter will get damaged due to flow of large amount of current through it, because it has low resistance.






Magnet: (i) is an object that attracts objects made of iron, cobalt & nickel.                                   (ii)  Comes to rest in North-South direction, when suspended freely.


Magnets are used: (i)  In radio & stereo speakers, (ii)  In refrigerator doors, (iii) in audio & video cassettes players, (iv)  On hard discs & floppies of computers & (v) in children’s toys.


Magnetic field:  The area around a magnet where a magnetic force is experienced is called a magnetic field. It is a quantity that has both direction & magnitude.


Magnetic field lines: Magnetic field is represented by field lines. They are lines drawn in a Magnetic field along which a North magnetic pole moves.  Magnetic field lines are called as Magnetic lines of force.

Refer to figure 13.3 & 13.4 page no. 225 of N.C.E.R.T  Text book)


Properties of Magnetic field lines: 

(i)                 They do not intersect each other.

(ii)        It is taken by convention that magnetic field lines emerge from

North pole and merge at the South pole. Inside the magnet, their

direction is from South pole to North pole. Therefore magnetic field

lines are closed curves.

v  Magnetic field lines due to a current through a straight conductor (wire)- consist of series of concentric circles whose direction is given by the Right hand thumb rule.

Right hand thumb rule: If a current carrying straight conductor is held in your right hand such that the thumb points towards the direction of current, then the wrapped fingers show the direction of magnetic field lines.

(Refer to figure 13.7, page no. 228 of N.C.E.R.T  Text book)

v  Magnetic field lines due to a current through a circular loop

(Refer to figure 13.8, page no. 228 of N.C.E.R.T  Text book)

The strength of the magnetic field at he centre of the loop(coil)depends on:

(i)                 The radius of the coil- The strength of the magnetic field is inversely proportional to the radius of the coil.  If the radius increases, the magnetic strength at the centre decreases.

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