Physics

Question 1

insulators can be charged by friction

Answer 1

• When two insulators move relative to each other, friction between the two can result in both objects becoming electrically charged.
• One of the objects becomes positively charged, and the other becomes negatively charged.
• Conductors, such as metals, can also become charged, but will only retain that charge if they are insulated from their surroundings. If they are not insulated, then any charge that builds up will leak away.

Question 2

It is also possible for objects to become charged by a

Answer 2

process called induction. Rather like when an unmagnetised piece of iron becomes magnetised when placed near a magnet, a neutral object placed near to a charged object can become charged:

Question 3

If one end of an object charged by induction is momentarily earthed,

Answer 3

• allowing the charge that has accumulated at that end to leak away, then the object becomes permanently charged:
• This is why uncharged objects (such as pieces of paper) can get attracted to charged objects (such as pieces of plastic) even though they are electrically neutral.

Question 4

rubbing 2 objects together?

Answer 4

When two objects are rubbed together, friction can result in electrons being transferred from one to the other. This results in the two objects becoming electrostatically charged. One object (the one that loses electrons) becomes charged positive, and the other (the one that gains electrons) becomes charged negative.

Question 5

it is always ????? that are responsible for electrostatic charge.

Answer 5

electrons

Question 6

the total charge always stays the?

Answer 6

same. One of the fundamental principles of physics is that charge is always conserved. So, for every object that becomes positively charged, another must become negatively charged.

Question 7

which atom becomes negatively charged and which becomes positively charged?

Answer 7

Which way the electrons move depends on which atoms attract the electrons more strongly. When two objects are rubbed together, electrons move away from the atoms that attract them less strongly, and towards the atoms that attract them more strongly. So whether a particular material becomes positively or negatively charged, when charged by friction, depends on the nature of the two materials involved.

Question 8

charging by induction?

Answer 8

It is electrons moving that are responsible for charging by induction. An object can become negatively charged by induction if electrons are attracted from Earth.

Question 9

Two charged objects placed near each other

Answer 9

• exert an electrostatic force on each other.
• The size of this force depends on the size of the two charges and the distance between them. The larger the charges, the larger the force, and the larger the distance of separation the smaller the force.
• The direction of the force depends on how the signs of the charges compare.

Question 10

what causes movement of charge during electrostatic induction?

Answer 10

It is attraction of electrons to positive charge, or repulsion of electrons from negative charge, that is responsible for the movement of charge during electrostatic induction.

Question 11

dangers of electrostatic sparking?

Answer 11

The risk of fires being caused by sparking is an aspect of electrostatic charging by friction that can make it very dangerous. An example of this is the risk of explosion when aircraft are refuelled.

Question 12

The risk of sparking can be eliminated by

Answer 12

earthing. If two objects, that would otherwise cause each other to become charged by friction, are connected together by a wire (or if one of them is connected to Earth by a wire) then electrostatic charging cannot take place and the risk is averted.

Question 13

To demonstrate that something is a permanent magnet

Answer 13

you need to demonstrate that it can repel another permanent magnet (attraction would only show that it is a magnetic material, not whether it is permanently magnetised).

Question 14

soft vs hard magnetic materials

Answer 14

Some materials, e.g. iron, steel, cobalt and nickel, are affected by magnetic forces and can become magnetised when they are placed in a magnetic field. The ease with which they become magnetised and lose their magnetisation varies from material to material:

Soft magnetic materials – are easy to magnetise but also easily lose their magnetisation.
Iron is an example of a ‘soft’ magnetic material.

Hard magnetic materials – are difficult to magnetise but once they are magnetised, they are difficult to demagnetise.
Steel is an example of a ‘hard’ magnetic material.

Note that being a soft or hard magnetic material has nothing to do with mechanical hardness!