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Physics > Static electricity > Flashcards

Static electricity Flashcards

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1
Q

What is the SI unit of electric charge

A

coulomb (C)

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2
Q

Define an electric field

A

An electric field is a region in which an electric charge experiences an electric force

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2
Q

What is the charge of a proton

A

1.6x10^-19 C

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2
Q

What is the charge of an electron

A

-1.6x10^-19 C

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3
Q

What is the conversation of electric charge

A

Conservation of electric charge states that electric charge cannot be created nor destroyed, and can only be transferred from one object to another

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4
Q

Do electric field lines go towards or away from a positive charge

A

Away

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4
Q

How are insulators charged

A
  • Friction
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4
Q

How are conductors charged

A
  • Contact
  • Induction
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4
Q

Do electric field lines go towards or away from a negative charge

A

Towards

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5
Q

How are insulators charged by friction

A
  • Before rubbing, both insulators are electrically neutral
  • Less tightly held electrons from fur are removed from their atoms and transferred to the rod
  • Rod has excess electrons and becomes negatively charged
  • Fur has deficit of electrons and becomes positively charged
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6
Q

How are conductors charged by contact

A
  • Positively charged rod touches neutral metal sphere
  • Free moving electrons from sphere flow towards rod as unlike charges attract
  • Metal sphere has deficit of electrons and becomes positively charged
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7
Q

How are 2 conductors charged by induction

A
  • Place 2 neutral metal spheres touching each other and on insulating stands
  • Negatively charged rod brought close to the right one
  • Free moving electrons in both spheres are repelled to far left end as like charges repel
  • Separate both spheres while rod is still close
  • Remove charged rod
  • Both spheres have equal number of excess opposite charges
  • Free moving electrons in each sphere redistribute themselves on sphere surface
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8
Q

Why are neutral insulators attracted to a charged object

A
  • Within insulator, electrons are not free moving but can move slightly within their own atoms
  • Electrons in insulator are attracted/repelled by charged object
  • Unlike charges between charged object and insulator become closer than the like charges
  • Force of attraction between unlike charges is greater than force of repulsion between like charges
  • Insulator is attracted to charged object as a whole
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9
Q

How is 1 conductor charged by induction

A
  • Place a neutral metal sphere on an insulating stand
  • Positively charged rod brought close to the sphere
  • Free moving electrons attracted to side nearer to rod as unlike charges attract
  • Earth the sphere by touching it without removing the rod, so flow of electrons from earth neutralises excess positive charges on sphere
  • Remove finger without removing rod
  • Remove the rod
  • Free moving electrons redistribute themselves equally apart on sphere surface
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10
Q

How are insulators discharged

A
  • Heating
  • Humid environment
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11
Q

How are conductors discharged

A
  • Earthing
12
Q

How are insulators discharged by heating

A
  • Heating ionises air around charged insulator
  • If insulator is positively charged, negative ions will be attracted to insulator to neutralise positive charges and vice versa
13
Q

How are insulators discharged by humid environment

A
  • Moisture on surfaces of charged insulator and in the air can conduct, leading to loss of static charges
13
Q

How do tankers prevent ignition of flammable substances due to electrostatic charging

A

Dangle a metal chain at the vehicle rear to provide an earthing path

14
Q

How are conductors discharged by earthing

A
  • Earth readily accepts or gives up electrons, acting as a charge reservoir
  • When earthed, path is provided for electrons to flow to conductor to neutralise excess positive charges or for excess electrons to flow from conductor to earth
15
Q

When can electrostatic charging be a hazard

A
  • Ignition of flammable substances
  • Electronics
  • Lightning

Physics (19 decks)

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