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Electromagnetism > Electric Currents > Flashcards

Electric Currents Flashcards

1
Q

what are conductors

A

materials which electrons are free to wander

  • electrons only loosely anchored to the atoms
  • all metals
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2
Q

what are insulators

A

materials in which electrons are not free to wander

  • electrons tightly bound and belong to particular atoms
  • rubber, glass, air plastics (which is why wires are covered with plastic)
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3
Q

What are semiconductors

A

neither good conductors nor good insulators

-can be used to control the flow of electrons

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4
Q

true or false; air is an insulator

A

true

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5
Q

During lightning millions of electrons move from a cloud to earth. How is this possible? describe 3 initial steps

A
  1. ) negative charge builds up on the bottom side of a cloud (through induction)
  2. ) electrons pulled away from the air molecules by the electric field
  3. ) if the electric field is sufficiently large the bond is broken and the electron is removed from the atom
    - insulator (air) is converted to conductor; as electrons are free to wander
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6
Q

What happens when the electric field between the ground and the cloud is strong enough?

A
  • air molecules are ionized (electrons kicked off)
  • a conductive plasma channel (gas of electrons and ionized molecules) form
  • electrons can move from the cloud to the ground via the plasma channel
  • cloud discharges (lightning)
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7
Q

Define electric potential

A

a charged object has the potential to do work by virtue of its location in an electric field

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8
Q

Define electric potential energy (U)

A

the energy a charged particle possesses by virtue of its location in an electric field

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9
Q

What does the U depend on

A

charge

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10
Q

true or false; the larger the charge the larges the potential to do work

A

true

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11
Q

what does work equal?

A

the change in potential energy

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12
Q

What does electric potential energy describes

A

how much a positive test charge wants to be at a given location

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13
Q

true or false; electric potential is independent of charge, dependent on location

A

true

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14
Q

what is the unit of electric potential

A

V

volts

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15
Q

electric potential= electric potential energy/ charge

A

true

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16
Q

For a positive test charge:
high potential: does not want to be there at all
low potential: wants to be there a lot
what about a negative test charge?

A

opposite
high potential: wants to be there
low potential: does not want to be there

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17
Q

true or false; electric potential decreases when moving away from positive charge and towards negative charge

A

true

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18
Q

direction of flow of electrons

A

low to high potential

19
Q

define electric current

A

flow of electric charge through a conductive medium

20
Q

what are the units of current

A

ampere (A)

21
Q

equation of calculating electric current, given the charge and time

A

I = Q/t

22
Q

direction of electron flow?

A

low to high potential

23
Q

direction of current flow?

A

high to low potential

24
Q

true or false; the electric field inside a current-carrying conductor is not zero

A

true

- electric field is only zero if there is no current (electric shielding)

25
Q

what is the direction of electric field?

A

same as the current

26
Q

how is potential difference maintained?

A

by doing work

27
Q

what must be maintained to keep the charge flowing?

A

potential difference

28
Q

true or false; eventually flow of charge will neutralize the potential difference

A

true

29
Q

What do batteries do?

A

maintain a constant voltage (potential difference) between the terminals

  • energy supplied by chemical reactions
  • current flows when terminals are connected
30
Q

what does the amount of current depend on?

A

voltage and resistance

- large voltage, large current

31
Q

what does resistance do?

A

opposes the passage of current

32
Q

what are the units of resistance?

A

ohms (Ω)

33
Q

What does ohms law say?

A

I = V/R

34
Q

What causes resistance

A

electric field accelerates electrons
electrons collide with positive ions and other electrons
- electrons have to be re-accelerated
- hinders their movement

35
Q

Electrons power (P)

A

rate of which electric energy is converted to another form

- energy lost by electrons on collisions is converted to eg. light

36
Q

equation of power

A

P= I*V

37
Q

true or false; electron energy at the positive terminal is zero (potential energy is zero and KE is negligible) so all energy is converted

A

true

38
Q

What is an electric circuit

A

any path along which electrons can flow

- for continuous flow, there must be no gaps

39
Q

What is a series circuit

A

all components are connected along a single path

40
Q

What is a parallel circuit

A

components form branches, each of which is a separate path for electrons

41
Q

Describe a parallel circuit

A
  • voltage remains the same in all components
  • current through each component obeys the Ohms law independently
  • total current equals the sum of currents through various components
    1/Rtot = 1/R1 + 1/R2 + 1/R3….
42
Q

Describe a series circuit

A
  • current flowing through each component is the same
  • voltage drops across each component
  • sum of voltages across each voltage equals the supply voltage
    Rtot = R1 + R2+ ….
43
Q

Define direct current

A

charge flows continuously in one direction

44
Q

define alternating current

A

direction of current alternates

  • cheaper for long distance transport (less power loss)
  • easier to make devices than for DC

Electromagnetism (3 decks)

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