27. What is the importance of coulomb's law in vector form?
Ans. (i)The forces between two charges are equal and opposite and they act on different bodies and they obey Newton's third law(ii)The electrostatic forces are Central forces
28. State two basic properties of charge
Ans. (i) Charge is additive
(ii) Charge is quantized
(iii) Charge is conserved
Ans. (i) Charge is additive
(ii) Charge is quantized
(iii) Charge is conserved
29. What is the value of charge on an electron in SI unit? Is a charge less than this value possible?
Ans. $e=-1.6\times 10^{-19}C$ Yes. For quarks charge can be $(1/3)e$ and $ (2/3)e$
Ans. $e=-1.6\times 10^{-19}C$ Yes. For quarks charge can be $(1/3)e$ and $ (2/3)e$
30. To identical metallic spheres of exactly school masses are taken. One is given a positive charge $Q$ and the other and equal negative charged by friction. Are there masses after changing equal?
Ans. No for positively charged sphere the mass will be decreased and for negatively charged sphere there will be an equal increasing mass due to excess of electrons.
Ans. No for positively charged sphere the mass will be decreased and for negatively charged sphere there will be an equal increasing mass due to excess of electrons.
31. Two large conducting spheres caring charges $ q_1$ and $q_2$ are brought closed to each other. Is the electrostatic force between them exactly given by $\frac{q_1 q_2}{4\pi \epsilon_o r^2} where $r$ is the distance between their centres?
Ans. No because due to electrostatic induction the distribution of charge on the sphere will change and this will affect the force between them.
Ans. No because due to electrostatic induction the distribution of charge on the sphere will change and this will affect the force between them.
32. If the distance between two equal point charges is doubled and their individual charges are also doubled, what would happen to the force between them?
Ans. $F \var \frac{q_1 q_2}{r^2}$. So there will be no change in the force.
Ans. $F \var \frac{q_1 q_2}{r^2}$. So there will be no change in the force.
33. If the distance between two equal point-charges is half and their individual charges are the doubled, what would happen to the force between them?
Ans. $F \var \frac{q_1 q_2}{r^2}$, $F^' \var \frac{4q^2}{{\frac{1}{2}}^2r^2}$ . The force will become 16 times the original force.
Ans. $F \var \frac{q_1 q_2}{r^2}$, $F^' \var \frac{4q^2}{{\frac{1}{2}}^2r^2}$ . The force will become 16 times the original force.
34. A charge $q$ is divided into two parts such that the repel each other with the maximum force when place at a certain distance apart. How has the charge been divided?
Ans. The chart should be divided into two equal halves. Let the two parts be $q_1$ and q- q_1.
Force$=\frac{1}{4 \pi \epsilon_o} \frac{q_1(q-q_1)}{r^2}$. The force is maximum when $\frac{dF}{dq_1}=0,$ $q-2q_1=0$ $\Rightarrow q_1= \frac{q}{2} $
Ans. The chart should be divided into two equal halves. Let the two parts be $q_1$ and q- q_1.
Force$=\frac{1}{4 \pi \epsilon_o} \frac{q_1(q-q_1)}{r^2}$. The force is maximum when $\frac{dF}{dq_1}=0,$ $q-2q_1=0$ $\Rightarrow q_1= \frac{q}{2} $
35. The force of attraction between two point charges at a distance $r$ apart is $F$ . What should be the distance apart in the same medium so that the force becomes $F/3$ . What if force becomes $3F$ ?
Ans. $F \var \frac{q}{r^2}, for $F/3$ , the distance should be $r\sqrt3$ and for $3F$ it should be $r/ \sqrt3 $
Ans. $F \var \frac{q}{r^2}, for $F/3$ , the distance should be $r\sqrt3$ and for $3F$ it should be $r/ \sqrt3 $
36. Is there any law limit of electric force between two charges $1 m$ apart in vacuum?
Ans. The lower limit will correspond to the least amount of charge which is equal to the charge of an electron.
$F=9×10^9×(1.6×10^{-19})^2/1^2=2.3×10^{-28} N$
Ans. The lower limit will correspond to the least amount of charge which is equal to the charge of an electron.
$F=9×10^9×(1.6×10^{-19})^2/1^2=2.3×10^{-28} N$
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