Tag: physics

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Multiple choice physics static electricity explaining static electricity charging by induction electric charges and fields

Rub a glass rod with a piece of silk. What happens?

  1. the glass has a slightly positive charge and the silk is also slightly positive

  2. the glass has a slightly positive charge and the silk is slightly negative

  3. the glass has a slightly negative charge and the silk is also slightly negative

  4. the glass has a slightly negative charge and the silk is slightly positive
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When a glass rod is rubbed with silk, both gets electrified due to charging by function by rubbing. One of the body acquires negative charge and other positive charge due to shifting of electrons from one body to other. Since silk has greater electron affinity (ability to attract electrons) as compared to glass. So, silk acquires slight negative charge and glass acquires slight positive charge.

Multiple choice physics static electricity explaining static electricity charging by induction electric charges and fields

A balloon gets negatively charged by rubbing ceilings of a wall.

  1. This implies that the wall is positively charged.

  2. This implies that the wall is negatively charged.

  3. This does not imply that the wall is positively charged.

  4. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A balloon gets negatively charged by rubbing ceilings of wall. But this does not imply that the wall is positively charged. The balloon induces a charge of opposite sign in the ceilings of the wall, causing the ceiling and the balloon to be attracted to each other. The balloon eventually falls because its charge slowly diminishes as it leaks to ground. Some of the charge on the balloon could also be lost due to the presence of positive ions in the surrounding atmosphere, which would tend to neutralize the negative charges on the balloon.

Multiple choice physics static electricity explaining static electricity charging by induction electric charges and fields

A comb run through ones hair attracts small bits of paper. What happens, if the hair are wet or if it is a rainy day? 

  1. The comb does not get charged and it will not attract small bits of paper.

  2. The comb does not get charged but it will attract small bits of paper.

  3. The comb does gets charged and it will attract small bits of paper.

  4. The comb does gets charged but it will not attract small bits of paper.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Comb gets electrically charged by friction when even through dry hair. It attracts small bits of paper because paper gets polarized in the presence if charged comb resulting in a net force of attraction. When hair is wet, the friction between comb and hair decreases and comb does not get charged. Hence, it may not attract small bits of paper.

Multiple choice physics static electricity explaining static electricity charging by induction electric charges and fields

A balloon gets negatively charged by rubbing ceilings of a wall. 

  1. The balloon sticks to the ceiling forever.

  2. The balloon eventually fall off the ceiling.

  3. The balloon does not stick to the ceiling at all.

  4. The balloon charges the ceiling negatively.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The balloon is negatively charged on rubbing with the wall means that on rubbing, the balloon collects electrons from the wall and making it negative in respect to the wall and therefore it clings to the wall, while clinging to the wall, the electrons on the balloon leaks off the balloon and eventually leaves. The balloon at the same potential as the wall, thus when the attraction between the balloon and wall is less than the weight of the balloon, the balloon eventually falls off. 

Multiple choice physics static electricity explaining static electricity charging by induction electric charges and fields

Which of the following charging methods work without ever touching the object to be charged to the object used to charge it?

  1. charging by friction

  2. charging by contact

  3. charging by induction

  4. all of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When a charge $Q$ is brought near (but not touching) an uncharged conductor, the charge $Q$ induces a charge of opposite polarity on the facing surface of the conductor and the same polarity on the rearer surface. This process of inducing a charge on the conductor without touching is known as charging induction.

Whereas charging by friction and contact work only when the surface of the two object are in contact with each other.

Multiple choice physics static electricity explaining static electricity charging by induction electric charges and fields

State whether the given statement is True or False :

When silk is rubbed with glass, the silk gets positively charged.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When silk is rubbed with glass, glass happens to lose electrons easily, and silk grabs them away from the glass atoms. So, after rubbing the glass becomes positively charged and the silk becomes negatively charged. 

Multiple choice physics static electricity explaining static electricity charging by induction electric charges and fields

When a body is charged by induction, then the body

  1. Becomes neutral

  2. Does not lose any charge

  3. Loses whole of the charge on it

  4. Loses part of the charge on it
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The part of the body nearer to the source charge gets induced charges, opposite in nature to the source charge while the other part gets those of similar nature.Thus no loss of charge.

Multiple choice physics static electricity explaining static electricity charging by induction electric charges and fields

A polythene piece rubbed with wool is found to have a negative charge of $3.6\times 10^{-7}C.$ Calculate the number of electrons transferred from wool to polythene:

  1. $6.25\times 10^{18}$
  2. $2.25\times 10^{12}$
  3. $2.05\times 10^{-18}$
  4. $2.18\times 10^{10}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$n=\dfrac {q}{e}=\dfrac {-3.6\times 10^{-7}C}{-1.6\times 10^{-19}C}$

$=2.25\times 10^{12}$
$\therefore 2.25\times 10^{12}$ electrons are transferred from wool to polythene.

Multiple choice physics static electricity explaining static electricity charging by induction electric charges and fields

A sure test of electrification is:

  1. attraction

  2. repulsion

  3. friction

  4. induction
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Repulsion is the sure test of electrification.
Note: If two bodies are electrified (i.e., charged they can either attract or repel). If they are:
(a) attracted: this is not only possible by electrification but can also be due to the attraction of an uncharged body with charged body.
(b) repulsion: repulsion is possible only when both objects are charged oppositely.