Electric Currents Flashcards Preview

Electromagnetism > Electric Currents > Flashcards

Flashcards in Electric Currents Deck (44):
1

what are conductors

materials which electrons are free to wander
- electrons only loosely anchored to the atoms
- all metals

2

what are insulators

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)

3

What are semiconductors

neither good conductors nor good insulators
-can be used to control the flow of electrons

4

true or false; air is an insulator

true

5

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

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

6

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

- 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)

7

Define electric potential

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

8

Define electric potential energy (U)

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

9

What does the U depend on

charge

10

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

true

11

what does work equal?

the change in potential energy

12

What does electric potential energy describes

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

13

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

true

14

what is the unit of electric potential

V
volts

15

electric potential= electric potential energy/ charge

true

16

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?

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

17

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

true

18

direction of flow of electrons

low to high potential

19

define electric current

flow of electric charge through a conductive medium

20

what are the units of current

ampere (A)

21

equation of calculating electric current, given the charge and time

I = Q/t

22

direction of electron flow?

low to high potential

23

direction of current flow?

high to low potential

24

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

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

25

what is the direction of electric field?

same as the current

26

how is potential difference maintained?

by doing work

27

what must be maintained to keep the charge flowing?

potential difference

28

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

true

29

What do batteries do?

maintain a constant voltage (potential difference) between the terminals
- energy supplied by chemical reactions
- current flows when terminals are connected

30

what does the amount of current depend on?

voltage and resistance
- large voltage, large current

31

what does resistance do?

opposes the passage of current

32

what are the units of resistance?

ohms (Ω)

33

What does ohms law say?

I = V/R

34

What causes resistance

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

35

Electrons power (P)

rate of which electric energy is converted to another form
- energy lost by electrons on collisions is converted to eg. light

36

equation of power

P= I*V

37

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

true

38

What is an electric circuit

any path along which electrons can flow
- for continuous flow, there must be no gaps

39

What is a series circuit

all components are connected along a single path

40

What is a parallel circuit

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

41

Describe a parallel circuit

- 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

Describe a series circuit

- 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

Define direct current

charge flows continuously in one direction

44

define alternating current

direction of current alternates
- cheaper for long distance transport (less power loss)
- easier to make devices than for DC