Important questions

---

---

» A positive charge of 16μC when flows from point A to B on its own, work done by the field on charge is 16×10−3J. What is the potential of A if potential of B is 1100 volt?

Ans. Using I = q/t                  {q = n e}

I = n e / t

$I=1$ A ,     $t=1$ s,    e= 1.6×10 −19  C

No. of electron = I t / e      

                            = 1×1 / 1.6 × 10^ -19

                            = 6.25 × 10¹² electron

---

---

» A piece of resistance wire has resistance of 16Ω. It is melted and reformed into a wire such that, its diameter is doubled. New resistance of the wire will be

Ans: R = length × area of cross section

 Resistance is inversely proportional to area or d^2/4. 

So, if diameter doubles the resistance will become 1/4 of initial value i.e., 4 ohm

---

---

» Two charges of equal magnitude and at a distance 'r' exert a force F on each other. If the charges are halved and distance between them is doubled, then the new force acting on each charge due to the other is

Ans: F = k q 1 × q 2  / r²

         F' = k q /2 × q /2 / (2r)²

         F' = F / 16

---

---

---

---

» Among identical spheres A and B having charges as $-5$C and $-16$ C. 

Ans: Potential due to a charged spherical conductor is given by, PE=(k∗q)/r.

Hence it will be higher for −5 coulomb.

---

---

» Two identical spheres A & B are charged uniformly with charge −5C and −16C respectively. What we can say about the the electric potential of two spheres?

Ans: Potential due to a charged spherical conductor is given by = (k × q) / r. 

Hence, it will be higher for -5 coulomb. 

---

---

---

---

»How many electrons per second will constitute a current of one micro ampere?

Ans: Current , $I=1\mu A=10^{-6}A$
We know that $Q=ne,t=1s$
Where $n$ is the number of electrons and e is the charge on $1$ electron and $e=1.6\times 10^{-19}C$

$I\; =\; n\; e$

$n\; =\; I/e\; =\; 10^-6\; /\; 1.6\; \times \; 10^-19\; =6.25\; \times \; 10¹²\; electron$

---

---

»What is the equivalent resistance between any two vertex of a triangle, if the sides of the triangle are of equal resistance R?

Ans: 1/R' = 1/R + 1/2 R

         1/R' = 3/2 R

         R' = 2R /3 

---

---

»Two parallel straight conductors carrying current in opposite direction will

Ans: If two parallel wires carry current in opposite directions, they repel each other whereas if two parallel wires carry current in same direction, they attract each other.

---

---

---

---