Electricity class 11 short questions

1. Define and write the unit of potential gradient in an electrostatic field.

Ans: Potential gradient is the rate of change of electric potential with respect to distance along the line of force is potential gradient. It is represented by dv/dx • It's SI Unit is V/m.

2. How is potential gradient related with the electric field Intensity?

Ans: we have, E=-dv/dx that is the electric field intensity at a point in an electric field can also be defined as the negative of the potential gradient at the point.The negative sign indicates that the direction of E is always in the direction in which the potential decreases.

3. Can a charged body attract on uncharged body? Explain.

Ans: Yes, it can be. when a charge of body is brought near to an uncharged body, opposite types charges (bound charges are induced at the closer end of the uncharged body and the same type of Charges (free charges) are induced at farther end. Due to this reason, there exists a tone of attraction between the bound charges & the charge on the charged body (inducing charge). Hence, the charged body attracts the uncharged body.

4. A man inside an Insulated metallic cage does not receive shock when the cage is highly charged why?

Ans. An insulated metallic cage hollow conductor. If we charge acts like a a hollow conductor all the charges reside on its outer surface but not inside the conductor. The potential at each point inside the cage is same as that on the surface Since there no potential difference between man and charged cage and electric field intensity is Zero. Hence, the man inside the cage does not receive any shock when the cage is highly charged.

5. Explain how a pitch ball can be electrified with positive or negative charge.

Ans:A pitch ball is a very small lightweight object that picks up electric charge the electrons in the - pitch ball are attracted to the positive rod and move close to the rod- Now, touch the positive side of the pitch ball from with a neutral object then the elections from the neutral object flow into the positive side of the pitch ball and we can get negatively charged pitch ball. Similarly, experiment can be carried out to charge positively by taking a negatively charged nd

6. Why does bodies get electrified when they are rubbed together for a while?

Ans: Bodies get electrified, when they are rubbed together for a while due to transfer or exchange of elections. When neutral substances are rubbed together, one of them loose the electron and another gains them. The substance which gains the electrons get negative charge and which loose electron gets positive charge.

7.What is electrostatic shielding?

Ans: when a hollow metallic conductor is charged all the charges will be distributed on its outer Surface.Inside the conductor, there will be no electric field.Hence a hollow conductor act as a shield due to which there will be zero electric field inside hollow conductor which is known as electrostatic shielding.

8.Two charged conductors are touched mutually and then separated what will be the charge them?

Ans: When two charged conductors are joined then there will be the flow of charge from higher potential to lower potential and finally the two surfaces become equipotential surface .when the two Conductors bre separated, the charges in the two conductors become constant since the charge in an isolated system is conserved.

9. Two positive charges separated by a distance create an electrostatic field. Can (i) electric potential, and (ii) electric field intensity be zero at a point between the charges ? Justify your answer..

Ans. If two charges are separated by certain distance then the electric field intensity will be zero at a point between the charges. It is because the electric field intensity by two charges will be equal and opposite at a point. So that the net electric field will be zero. But, if E is zero at a certain point electric potential V does not have to be zero.The electric field intensity at a point is negative of the potential gradient i.e.E= -dv/dr .If E= 0 Then dv=0 or V= constant. The constant may or may not be zero

10. The tyres of aeroplane are made from a special rubber which is reasonably good conductor of electricity. what would be the reason behind it?.

Ans: During the motion of the air crafts on run way, the friction bet The tyres and the run electrification of tyres. If the tyres are non- conducting excessive charge will accumulate on the tyres which may cause sparkling. If the tyres of the air craft are made slightly conducting,the accumulated charge can flow to the earth through the tire eliminating any danger of fire.

11. More charge can be stored on a metal if it is high polished that when its surface is rough. Explain.

Ans: If the surface of the metal is highly polished, then charges are uniformly distributed over this surface. Hence, the charge density throughout this surface remains constant and so leakage of charge due to action of point is reduced from such surface. On the other hand, if the surface of the charged metal sphere is rough, there are large no of small pointed ends and the charge density at these ends (σ = Q/A) is high. So, due to action of points the possibility of leakage of charges from the rough surface increases. Due to this reason, more charge can be placed on a metal if it is highly polished than when it surface is rough.

12.Why are The four footed animals posed to more threat during close by lightning strike than the two tooted humans?

Ans: Animals have wider steps, maybe 1.5 or two meters wide, so the step voltage is much higher. The current, if it flows through the front and back legs, will always flow through the animal's heart. So the risk of death is much higher for animals during such an event.

13.why is it dangerous to take shelter under a tall tree during lightening?

Ans: Lightining occurs because clouds becomes negatively charged as the water droplets inside rub up against each other during the natural process of evaporation and condensation, when moisture accumulates in the clouds. It always takes the quickest path to to the ground and usually strikes tall isolated objects such as tree, which can cause injury even death of person taking shelther under the tree. Hence, it is dangerous to take shelther under a tall tree during lighting.

14. Sharp projections are avoided in machines why ?

Ans: we know

σ = Q/A

Since, surface density of charge is maximum at the pointed ends, so due to the action of points the possibility of leakage of charge from the pointed ends (sharp projections) is more, so, that machines does not perform well. That's why sharp projection are avoided in machines to prevent the leakage of Charge from the machine in the surrounding.

15. What do you mean by charging by conduction and charging by induction.

Ans: When one Charged body is brought in contact with another uncharged body then there is flow of charge from charged to uncharged body as a result uncharged body becomes charged. This method of of charging a body is called charging by conduction.

When one charged body is brought close to an uncharged body (without touching), the uncharged body becomes charged. This method of charging a body by bringing a charged body near to it is charging by induction.

16. Some of the free electrons in a good con ductor (such as a piece of copper) move at speeds of 10^6 m/s or faster. Why don't these electrons fly out of the conductor completely ?

Ans:when the free election moves faster the some number of positive charge is developed in the conductor due to which the coulomb force of attraction is developed between the opposite charges and the elections don't fly away from the conductor completely.

17.Define electron volt.

Ans. The energy gained by an electron when accelerated through a potential difference of one volt is called election volt. (1 eV= 1.6X10^-19 J )

18.Prove 1 V/m = 1 N/C

Ans: we have

1 v/m = 1 J/c/m [.•. V=J/C]

= 1 Nm/c/ m [.•. 1J= 1Nm]

= 1 N/C

19. What is meant by relative permittivity? What is its minimum value?

Ans: Relative permittivity (or dielectric constant) i defined as the ratio of absolute permitivity of any medium to permittivity of air or vacuum. It is denoted by K or ∈r

i.e. ∈r = ∈/∈o

It's minimum value is 1.

20 . Bits of paper are attracted to an electrified comb, even though they have no net charge. How is this possible?

Ans: When an electrified comb is brought near bits of paper, the election on the paper one repelled and positive change will be nearer to The comb due to induction Due to this, there is force of attraction between the electrified comb and neutral paper.

21. Can two electric lines of force intersect each other? Explain.

Ans: No, two electric lines of force never intersect each other. The tangent at any point a line of tore gives a direction of point in field intensity at that point. It two lines of force in an electric field would intersect, two tangents can be drawn at the point of intersection This means, there are two directions for electric field intensity at this point of intersection, which is impossible this is because there is only one direction of electric field intensity at point in an electric field.

22. What do Explain you mean by quantization of change?

Ans: The charge on a body is always an integral multiple of a basic unit of change i.e.+1.6 X 10 C. i.e. Q = ne where & is the charge on the body, n= 1,2,3,... and e be the charge or the a proton or an election. The fact that the charge on a body is always fixed integral multiples of the smallest unit but not intermediate values, is known as quantization of charge.

23 . We often experience the sparks during the winter night's when removing the cloths from our body Why?

Ans: In winter season, our body is dry but not wet because of which friction is produced while removing clothes causing some exchange or transfer of electrons between body & cloth which causes sparks so we often experience the sparks during the winter night when removing the cloths from our body.

24. Why metallic chain is used in the tanker transporting highly inflammable liquid?

Ans. During motion ,tanker gets charged due to the friction with air and the tyres also get charged due to the friction with road In case, charge accumulation becomes large, it may very dangerous to the tanker and can get fire. Hence, they have metallic chain allowing accumulating charge to flow to the earth.

25. Is it possible that electric potential at a point is zero but not electric field?

Ans: Yes, electric potential can be zero at a point but not electric Held At the midpoint bets the charges, the eclectic potential due to the charges is zero, but the electric field due to the changes” at the same point non-zero

26. Is it possible that electric field is zero at a point but not electric potential &

Ans: Yes, it is possible that electric field is zero at a point but not electric potential E.g.: Inside the hollow spherical charged conductor, electric field is zero but potential is not zero..