Question

You take two invisible tapes of some unknown brand, stick them together, and discharge the pair before pulling them apart and hanging them from the edge of your desk. When you bring an uncharged plastic pen withinof$10\mathrm{CM}$ either the U tape or the L tape you see a slight attraction. Next you rub the pen through your hair, which is known to charge the pen negatively. Now you find that if you bring the charged pen withinrole="math" localid="1655718752350" $8\mathrm{CM}$of the L tape you see a slight repulsion, and if you bring the pen withinrole="math" localid="1655718766744" $12\mathrm{CM}$of the U tape you see a slight attraction. Briefly explain all of your observations.

Short answer

Thus, the uncharged pen is first attracted to the U and the L tape due to the concept of charging by induction, and when it got negatively charged after rubbing, then the pen got repulsed from the L tape as it is of negative charge and the pen got attracted to the U tape as it is of positive charge

Step-by-step solution

Significance of the law of attraction and charging by induction for the tapes and pen

The law of attraction states that the unlike charges attract each other and the like charges repel each other.

Charging by induction states that an uncharged particle can get charged if it is kept beside a charged particle.

The law of attraction and the charging by induction gives the reason for the attraction of the pen with the U and L tape.

Determination of the reason for the attraction and repulsion

As the invisible tape has been sticked together, then both the tapes have induced some charges. However, after discharging the tapes, the U tape has induced a positive charge and the L tape has induced a negative charge. So, when the uncharged pen is brought towards either the L tape or the U tape within a distance of, then the pen gets attracted towards the tapes and this is due to the reason that uncharged particles get attracted towards the changed one according to the concept of charging by induction.

As the pen is negatively charged after rubbing on hairs, then when it is brought to a distance oftowards the L tape which is negatively charged, a slight repulsion occurred due to the reason that like charges repel each other according to the law of attraction.

Now, when the negatively charged pen is brought at a distance oftowards the U tape which is positively charged, a slight attraction occurred due to the reason that unlike charges attract each other according to the law of attraction.

Thus, the uncharged pen is first attracted to the U and the L tape due to the concept of charging by induction, and when it got negatively charged after rubbing, then the pen got repulsed from the L tape as it is of negative charge and the pen got attracted to the U tape as it is of positive charge.