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ICSE Class 9 Physics Question 15 of 18

Current Electricity — Question 11

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Question

Question 11

While performing an experiment, a student reduces the resistance to one half keeping the potential difference same. New reading of the current will be :

  1. half
  2. double
  3. four times
  4. one fourth
Answer

double

Reason — Let initial and final current be I and Inew, initial and final resistance is R and Rnew and initial and final potential be V and Vnew

From Ohm's law,

Case 1 :

V=IR\text V = \text {IR}

Case 2 :

Vnew=InewRnew\text V_{\text {new}} = \text I_{\text {new}}\text R_{\text {new}}

According to question,

Vnew=V  and  R<em>new=12R⇒I</em>newRnew=IR⇒Inew×12R=IR⇒Inew2=I⇒Inew=2I\text V_{\text {new}}=\text V\ \text { and}\ \text { R}<em>{\text {new}}=\dfrac {1}{2}\text R\\[1 em] \Rightarrow \text I</em>{\text {new}}\text R_{\text {new}} = \text {IR} \\[1 em] \Rightarrow \text I_{\text {new}}\times \dfrac{1}{2}\text R = \text {IR} \\[1 em] \Rightarrow \dfrac{\text I_{\text {new}}}{2} = \text I \\[1 em] \Rightarrow \text I_{\text {new}} = 2\text I