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CLASS - 10 SCIENCE IMPORTANT QUESTIONS OF MARK 5   FOR BOARD EXAMINATION

QUESTION NO. 15

(a) With the help o suitable circuit diagram prove that the reciprocal of equivalent resistance of a group of resistances joined in a parallel is equal to the sum of the reciprocals of the individual resistances.

(b) In an electric circuit two resistors of 12 ohm are joined in parallel to a 6V battery. Find the current drawn from the battery.

ANSWER NO. 15 

There resistors R1, R2 and R3 are connected in parallel.
The total current I, is equal to the sum the separated currents through each resistor R1, R2 and R3.



I = I1 + I2 + I3           ----------------------------(1)
  Let Rp be the equivalent resistance of the parallel combination of resistors. By applying ohm's law to the parallel combination of resistors.
                 I = V/Rp                (V = IR)
  On applying ohm's law to each resistors, we have 
  I1 = V/R1  ,  I2 = V/R2  and I3 = V/R3    -------------------(2)
         From equation (1) and (2) -
V/Rp = V/R1 + V/R2 + V/R3
V(1/Rp) = V(1/R1 + 1/R2 + 1/R3)
   1/Rp =1/R1 + 1/R2 +1/R3

 Thus the reciprocal of the equivalent resistance of a group of resistances joined in parallel is equal to the sum of the reciprocals of individual resistances.

 (b) Total resistance in the circuit 1/R = 1/R + 1/R            =  1/12 + 1/12
    1/R = 2/12
    1/6 = 1/6
    R = 6 ohm
R = 6 ohm, V  =6 volt
V/I = R , IR = V , I = V/R = 6/6 = 1 ampere
current drawn by the battery = 1 ampere.

QUESTION NO. 16

What is a solenoid ? Draw the pattern of magnetic field lines of.
(i) A current carrying solenoid and
(ii) A bar magnet
List two distinguishing features between the two fields.

ANSWER NO. 16

SOLENOID

A solenoid is a generic term for a coil of wire used as an electromagnet. It also refers to any device that convert electrical energy to mechanical energy using a solenoid. The device creats a magnetic field from electric current.
(i) The magnetic field for the current carrying solenoid.




(ii) FOR BAR MAGNET



  1. The poles of the bar magnet do not lie exactly at end of the magnet but are somewhat inside. In a solenoid, poles can be considered to be lying at the edge. 
  2.  The magnetism retains in the bar magnet naturally but in the solenoid, the magnetism is there so long current flows through it.

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