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Electric Charge Flashcards

1
Q

What is an electrophorus?

A

A device for transferring and storing charges.

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2
Q

How does an electrophorus produce electric charges?

A

By electrostatic induction.

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3
Q

Describe the components of an electrophorus.

A

It consists of a circular metal disc or plate with an insulating handle and a flat disc made of an insulating material like ebonite or polythene.

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4
Q

How is the electrophorus used to store charges?

A

The ebonite or polythene disc is given a negative charge

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5
Q

Why don’t charges flow between the two discs when the metal disc is placed on the ebonite disc?

A

Because there are only a few contact points between the discs.

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6
Q

What type of charges are given to the metal disc by electrostatic induction?

A

Positive and negative charges.

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7
Q

What happens when the metal disc is touched with a finger?

A

The negative charges flow away to the earth.

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8
Q

What charge remains on the metal disc after touching it with a finger?

A

Only positive charges.

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9
Q

Where are the charges stored in an electrophorus?

A

In the metal disc when it is lifted from the ebonite.

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10
Q

Can the amount of charge stored in an electrophorus be increased?

A

Yes

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11
Q

Where are charges most highly concentrated on a conductor?

A

At the sharp points.

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12
Q

What happens when a highly charged pointed conductor is placed in the air?

A

It causes the air around the sharp point to be ionized.

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13
Q

Explain the process of ionization around a positively charged sharp point.

A

The high charge density attracts negative ions and repels positive ions

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14
Q

What is the result of this ionization process?

A

An avalanche of ions causes the surrounding air molecules to be dragged along

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15
Q

What is the movement of ions towards the charged point known as?

A

Point action.

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16
Q

What are lightning flashes?

A

Dramatic displays of electrical discharges in nature.

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17
Q

How are lightning flashes formed?

A

By the buildup of electrical charges in thunderclouds and the sudden jump of opposite charges between clouds or from cloud to earth.

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18
Q

What is the purpose of a lightning conductor?

A

To provide a safe path for electrical discharges and protect buildings from damage.

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19
Q

Describe the structure of a lightning conductor.

A

It consists of sharp pointed metal rods or spikes at the highest point of a building

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20
Q

Why is a thick copper cable used in a lightning conductor?

A

To carry a large current without melting.

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21
Q

How does a lightning conductor work?

A

The sharp points induce charges opposite to those of the cloud

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22
Q

How is the distribution of charges over the surface of an insulated pear-shaped conductor examined?

A

By charging the conductor using electrostatic induction and using an electroscope and a proof plane to examine the charge distribution.

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23
Q

Where are charges usually concentrated on a conductor?

A

At places where the surface is sharply curved.

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24
Q

Define charge density.

A

The charge per unit area of surface.

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25
Where is the charge density highest on a conductor?
At the sharpest point of the conductor.
26
Why is the charge density highest at the sharpest point of a conductor?
Because the sharpest point has the smallest surface area and the greatest concentration of charges.
27
Where does the charge on a hollow conductor collect?
Only on its outside surface.
28
How can an electroscope be used to distinguish between conductors and insulators?
By touching the cap of a charged electroscope with a body and observing the effect on the leaves. A rapid collapse indicates a good conductor
29
What happens to the leaves of a charged electroscope when touched with a finger?
The leaves collapse
30
How can a gold leaf electroscope be used to test the sign of the charge on an object?
By observing the effect on the divergence of the leaf when the charged body is brought near the metal cap of the electroscope.
31
What does an increase in the divergence of the leaf indicate?
That the charge on the electroscope and that of the test charge are the same.
32
Does a decrease in the divergence of the leaf always indicate the presence of a charged body?
No
33
How is the magnitude of the charge measured using an electroscope?
By the degree of divergence of the leaf. A greater degree of divergence indicates a greater amount of the test charge.
34
What is an electroscope?
An instrument used for the detection and testing of small electric charges.
35
Describe the essential features of a gold leaf electroscope.
It consists of a flat brass disc or cap
36
What is the purpose of the metal case surrounding the rod and leaf?
It insulates the brass rod and makes the setup draught-proof with glass sides for clear visibility of the leaf.
37
Why is the metal case normally connected to the earth?
To prevent the accumulation of charges due to external influence.
38
What are the two terminals of the gold leaf electroscope?
The flat brass disc and the earthed metal case.
39
What does the position of the leaf indicate?
The presence of charges in the disc and rod.
40
How can an electroscope be charged by contact?
By sliding a charged body on the brass disc of the instrument.
41
What happens to the leaf when an electroscope is charged by contact?
The leaf opens or diverges.
42
What does the degree of divergence of the leaf indicate?
The amount of charge acquired by the electroscope.
43
Does the leaf return to its original position after the charging body is removed when charging by contact?
No
44
What is the nature of the charge acquired by the electroscope when charged by contact?
The same as that of the charging body.
45
How can an electroscope be charged by electrostatic induction?
By bringing a charged rod near the cap of the electroscope without touching it.
46
What happens to the leaf when an electroscope is charged by induction?
The leaf diverges.
47
What are the four steps to charge an electroscope by induction with a negatively charged rod?
1) Bring the negatively charged rod near the cap. 2) Touch the cap with a finger. 3) Remove the finger. 4) Remove the rod.
48
What is the charge induced on the electroscope when charged by induction with a negatively charged rod?
A net positive charge.
49
What is the charge induced on the electroscope if a positive rod is used for charging by induction?
A net negative charge.
50
How are substances classified in static electricity?
According to the degree of resistance they offer to the passage of electrons.
51
What are the two groups of substances based on their ability to conduct electricity?
Conductors and Insulators.
52
Define conductors.
Materials that allow electrons to pass through them easily.
53
Give examples of conductors.
Almost all metals
54
Define insulators.
Materials that do not allow electrons to pass through them easily.
55
Give examples of insulators.
Plastic
56
What is the general rule regarding the conductivity of heat and electricity?
Good conductors of heat are also good conductors of electricity.
57
How should metals be supported when charged?
With insulating materials.
58
Why should metals be supported with insulating materials when charged?
To prevent the charges from flowing through the human body to the earth.
59
What are the three methods of producing electric charges?
Friction
60
Describe how charges are acquired by friction.
Charges are acquired by friction between two materials
61
What is the result of rubbing an ebonite rod with fur?
Negative charges are produced on the rod
62
What is one practical example of charges acquired by friction?
Moving vehicles becoming charged by passage through the air
63
Why do people sometimes experience a slight electric shock when stepping out of cars?
The friction between the air and the car's body causes electric charges to collect on the vehicle.
64
How can the accumulation of electrostatic charges be prevented in petrol tankers?
A chain or metal strip is often left hanging from the rear of petrol tankers to neutralize the charges by passing them to the earth.
65
Describe how an electroscope can be charged by contact.
An electroscope can be charged by touching its brass cap with a charged object
66
What type of charge does an electroscope acquire when charged by contact?
The same type of charge as the charging body.
67
Explain how two uncharged conductors (C and D) on insulating stands can be charged by contact.
By bringing a charged rod near one conductor (C) and then separating the conductors while the rod is still near
68
What is the disadvantage of charging by contact?
It is not a very efficient method.
69
Explain how a body can be charged by electrostatic induction.
By bringing a charged object near an uncharged conducting body
70
What happens when a negatively charged ebonite rod is brought near an uncharged conductor?
The end of the conductor near the rod becomes positively charged
71
How can the charge on a conductor be made permanent during electrostatic induction?
By touching the conductor with a finger to earth it while the inducing charge remains
72
What is an electroscope?
A simple apparatus for detecting the presence of electric charges and identifying their nature.
73
What is a simple electroscope?
A simple electroscope consists of a metal rod with a metal cap at the top and thin metal leaves at the bottom
74
What happens to the leaves of an electroscope when a charged object is brought near the cap?
The leaves diverge or separate.
75
What causes the divergence of the leaves of an electroscope?
Electrostatic induction.
76
How can an electroscope be charged by contact?
By touching the cap with a charged object.
77
What charge does an electroscope acquire when charged by contact?
The same charge as the charging body.
78
How can an electroscope be charged by induction?
By bringing a charged object near the cap and then grounding the electroscope.
79
What charge does an electroscope acquire when charged by induction?
The opposite charge to the charging body.
80
What is the focus of the chapter on electric charges?
Electrostatics or static electricity.
81
Describe electrostatics or static electricity.
A type of electricity that does not move from one point to another in the substance in which it is produced.
82
What is the study of electrostatics?
The study of charges at rest.
83
What are the main topics discussed in the chapter?
The ways of producing electric charges
84
What are the three methods to charge a body?
Friction
85
What are the two types of electric charges?
Positive and negative charges.
86
How is positive charge produced?
By rubbing a glass rod with silk.
87
How is negative charge obtained?
On an ebonite rod by rubbing it with fur.
88
What happens when a glass rod rubbed with silk is brought near another glass rod rubbed with silk?
Repulsion.
89
What happens when an ebonite rod rubbed with fur is brought near a glass rod rubbed with silk?
Attraction.
90
What is the charge acquired by an ebonite rod rubbed with fur?
Negative charge.
91
What is the charge acquired by a glass rod rubbed with silk?
Positive charge.
92
Name two materials that can be used to obtain a positive charge when rubbed with silk.
Cellulose acetate strip.
93
Name a material that can be used to obtain a negative charge when rubbed with fur.
Polythene rod.
94
What is the rule regarding the interaction between like charges?
Like charges repel each other.
95
What is the rule regarding the interaction between unlike charges?
Unlike charges attract each other.

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