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This is one of our many quizzes on Electricity and current. Click on this to access more such competitive quizzes on Current Electricity.

Electricity and current Quiz 2

physics

 Vishnu when working in his lab found that the measurement shown in a voltmeter is $5\text{ units}$ and the readings shown in the multimeter when connected across the copper wire has been mentioned as $6\text{ units}$. What will be the reading shown in the ammeter connected across the same circuit? 

 According to Ohm's law, voltage will be directly proportional to the current where the constant of proportionality is resistance. 

  $\text{According to Ohm’s law,} \\ V=IR \\ \Rightarrow \text{Reading in the voltmeter=reading in the ammeter}\times \text{reading in the multimeter} \\ \text{Substituting the values,} \\ \Rightarrow 5=I\times 6 \\ \text{Rearranging,} \\ I=\dfrac{5}{6} \\ \therefore I=0.833\text{ }A$

 Veena once passed some amount of electric current through a wire of resistance, $2\text{ }J$ of heat was generated in the wire. If we assume the value of current is $0.6\text{ }A$and the resistance of the wire be $8\text{ }\Omega $, how much time did it take to generate this amount of heat? 

 Heat generated will be the product of the square of the current flowing, resistance of the wire and the time taken. 

  $\text{The equation of heat generated,} \\ H={{I}^{2}}Rt \\ \text{Rearranging the equation}, \\ t=\dfrac{H}{{{I}^{2}}R} \\ \text{Substituting the values in it,} \\ t=\dfrac{2}{{{\left( 0.6 \right)}^{2}}\times 8} \\ \Rightarrow t=\dfrac{2}{2.88} \\ \therefore t=0.694\text{ s}$

 Mohit once had a doubt. He went to his father and asked “Why did a bird sitting on a single electric lane didn’t get an electric shock?” What will be his father’s answer if he answered correctly? 

 The electric will flow only when there is a closed loop formation. Otherwise no current can flow through the body or wire. 

 If a bird is sitting on a single electric lane, it will not have any issue as there is no formation of an electric circuit. So the bird will be safe. Once it touches the other electric line too, then there will be a formation of closed circuit loop and hence the bird’s body will conduct electricity and electrocution happens.

 Madhav when connected a current source to a machine he invented a day before, found that the power of the machine becomes $64$ times when the value of current increased to a certain value.Calculate the value of current if the initial value of current was $0.6\text{ }A$? 

 The power of the body will be proportional to the product of the square of the current and the resistance. 

 $\text{The equation of power,} \\ P={{I}^{2}}R \\ \text{If the initial power be }{{\text{P}}_{\text{1}}}\text{ and final power be }{{\text{P}}_{\text{2}}}, \\ \text{Taking the ratio,} \\ \dfrac{{{P}_{1}}}{{{P}_{2}}}=\dfrac{{{I}_{1}}^{2}R}{{{I}_{2}}^{2}R} \\ \text{Cancelling the common terms,} \\ \dfrac{{{P}_{1}}}{{{P}_{2}}}=\dfrac{{{I}_{1}}^{2}}{{{I}_{2}}^{2}} \\ \text{Substituting the values,} \\ \dfrac{{{P}_{1}}}{64{{P}_{1}}}=\dfrac{{{\left( 0.6 \right)}^{2}}}{{{I}_{2}}^{2}} \\ \Rightarrow \dfrac{1}{64}=\dfrac{{{\left( 0.6 \right)}^{2}}}{{{I}_{2}}^{2}} \\ \Rightarrow 64=\dfrac{{{I}_{2}}^{2}}{0.36} \\ \Rightarrow \text{Rearranging,} \\ \Rightarrow {{I}_{2}}^{2}=64\times 0.36 \\ \Rightarrow {{I}_{2}}=8\times 0.6 \\ \therefore {{I}_{2}}=4.8\text{ }A$

 Meenakshi once found that when a $0.694\text{ A}$current passes through a wire, the reading shown by the voltmeter is $5\text{ }V$. Calculate the length of the wire if the area of cross section is <br>(a)$\,5\text{ }{{m}^{2}}$<br>(b)$\,3.9\text{ }{{m}^{2}}$<br>Let us assume that the resistivity of wire be $2.88\text{ }\Omega m$. 

 In accordance to Ohm’s law, the product of the current flowing and the resistance will be equivalent to the potential difference. 

 $\text{According to the Ohm’s law,} \\ V=IR \\ \text{Rearranging the equation,} \\ R=\dfrac{V}{I} \\ \text{Substituting the values,} \\ \text{R=}\dfrac{5}{0.694} \\ \Rightarrow R=7.2\text{ }\Omega  \\ \text{The equation of resistance,} \\ R=\dfrac{\rho l}{A} \\ \text{(a) Substituting the values}, \\ 7.2=\dfrac{2.88\times l}{5} \\ \text{Rearranging,} \\ l=12.5\text{ }m \\ \text{(b) Substituting the values in it,} \\ 7.2=\dfrac{2.88\times l}{3.9} \\ \text{Rearranging,} \\ \Rightarrow l=\dfrac{7.2\times 3.9}{2.88} \\ \therefore l=9.75\text{ }m$