QNR 12. Read the following passage and answer the questions that follow:
Everything on this planet is made up of atoms. Each atom contains a positively charged centre, or nucleus, which is surrounded by negatively charged electrons. For most objects, the number of positive charges is equal to the number of negative charges and because they cancel each other out, the object ends up with no overall electric charge. However, it is possible for objects to gain an overall negative or positive charge.When objects made of different materials are rubbed together, electrons may jump from one object to the other. Objects become positively charged if they lose electrons and negatively charged if they gain electrons. You can predict which way the charges will jump by referring to a triboelectric chart such as the one shown here.
This list of common materials is arranged in order of how likely they are to lose electrons. In general, when two materials are rubbed together, the material that is higher on the list will lose electrons to the materials listed below it. For example, if a perspex rod is rubbed with a piece of wool, the wool will lose electrons to the perspex so the wool will end up with an overall positive charge and the perspex will end up negatively charged. The further apart the materials are on the list, the more easily the electrons are transferred between them (which means that you don’t have to rub them together very long to get them to charge up). If you were to rub glass with rabbit’s fur, far fewer electrons will move to the glass than if you were to rub the rabbit fur on something like ebonite.
(i) Which of these four materials, when rubbed against each of the other three, will become positively charge each time?
4) plastic wrap
(ii) Which of the following objects has an overall negative charge?
(iii) Cotton will gain most electrons when it is rubbed for one minute against
4) cat’s fur
Objects that have opposite electric charges move towards each other while objects that have the same electric charge push each other away.A charged objects and uncharged object will move towards each other. The diagram below show that what happens when different balloons are hung on strings near each other or near a charged object.
(iv) What are the overall charges on the balloons?
(i) Which of these four materials, when rubbed against each of the other three, will become positively charge each time? –> This essentially is asking which material has the maximum chances of becoming positive when rubbed against the rest three or which material lies high up in the table than the rest three.
As you can see in the below chart, Perspex is higher than rest. Option (1).
(ii) This is straightforward. If negatives are more than the positives it will lead to an overall negative charge. Option (2) B. Also A -> Neutral, C -> Overall positive, D -> Overall Positive.
(iii) Let us quickly mark the elements in question:
Firstly Cotton will gain electrons when it is rubbed with objects that lie above its position in the table; so Perspex and Acrylic are reject out. Cat’s fur lies above Silk so it will have the higher ability to lose electrons to become more positive. Option (4) is the answer.
(iv) In the diagram, it shows that B moves away from an overall positively charged object. This signifies B is positive. In the second diagram, B and A are shown attracted towards each other; this tells A is either “neutral” or “negative”. Only option (3) is possible as given in the table.