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Physics > Electricity And Magnetism > Flashcards

Electricity And Magnetism Flashcards

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1
Q

We define Electric current (I) as the rate of flow of net charges through a selected area in a unit of time

A

I = Q / t

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2
Q

Electric current (I) is: a scalar or vector

A

scalar

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3
Q

SI unit (measurement) of Electric current (I) :

A

ampere

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4
Q

One ampere =

A

one coulomb per second

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5
Q

Electrons rapidly collide with ions, even with the absence of the Electric Field (E).

A

In metals and other conductors

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6
Q

In a conductor, an electron with a charge (q) acquiring extra kinetic energy due to work of the external force (F) of the electric field (E).

A

F = qE

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7
Q

Voltage (V) between two points is defined as electric field (E) times the displacement ( lower case L ) between these two points.

A

V = E l

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8
Q

Voltage is a: scalar or vector

A

Scalar

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9
Q

SI unit (measurement) of voltage:

A

Volt

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10
Q

Volt =

A

Walt over ampere (W/A)

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11
Q

Batteries are common sources of:

A

fixed voltage &

relatively constant voltage.

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12
Q

Power outlets are sources of:

A

oscillating voltage

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13
Q

The proportionality of the electric current inside a conductor to the electric field is expressed in Ohm’s Law:

A

V = I R

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14
Q

V = I R

A

(V) voltage applied to the piece of conductor (such as wire)
(I) electric current through the conductor
(R) electric resistance of the piece of material

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15
Q

Electric resistance (R) - being a ratio of two scalars- is :

A

scalar

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16
Q

The SI unit (measurement) of Electric resistance (R)

A

Ohm

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17
Q

Ohm =

A

Volt over ampere (V/A)

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18
Q

Kirchoff’s laws for electric circuits:

A

Loop rule: Voltage drop across a closed circuit loop is zero. ( V - IR = 0 )
Branch rule: Net current into a single circuit branch is zero. ( I = I1 + I2 )

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19
Q

Using Kirchoff’s law and Ohm’s law it is easy to derive total resistance of a circuit for resistors in series and resistors in parallel.

A

( R = R1 + R2 + R3 ) resistors in series

1/R = 1/R1 + 1/R2 + 1/R3

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20
Q

In many conductors, the current is proportional to:

A

The applied electric field (E) (and voltage)

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21
Q

A simple example of an electric current is:

A

an incandescent lamp

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22
Q

Measures resistance to the flow of electricity:

A

Ohm

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23
Q

Voltage source that converts chemical energy to electrical energy:

A

Battery

24
Q

The unit and symbol for current

A

Ampere, I

25
Q

Something that allows electricity to pass through it:

A

Electrical conductor

26
Q

Magnets exert magnet force on:

A

Iron objects

27
Q

Magnetic forces originate from:

A

moving electric charges

28
Q

Elementary particles like electrons:

A

behave like little magnets

29
Q

Prime examples of usefulness of magnetic force:

A

Electric power generators

Electric motors

30
Q

Strong magnetic fields are used in:

A

MRI’s

microwave ovens

31
Q

Earths magnetic field enabled:

A

The compass. (the needle always aligns itself with the magnetic field lines)

32
Q

Magnetic field lines:

A

don’t originate in a single point.

33
Q

The connection between electric and magnetic forces was first discovered by:

A

Oersted in 1819.

34
Q

Found that moving a magnet near a conducting loop induces electric current and likewise, changing current inside a conducting loop will induce electric current in a nearby conducting electic loop.

A

Faraday

35
Q

Magnetic field strength (B) is a: scalar or vector

A

vector

36
Q

SI unit (measurement) of magnetic field strength (B):

A

(N/Am) Newton per ampere meter

37
Q

(N/Am) =

A

(T) Tesla

38
Q

The magnetic force points in the direction perpendicular to the plane that is defined by:

A

the velocity vector and the magnetic field vector.

39
Q

The magnitude of the Lorentz force on a single particle where (q) is the charge of the particle, (v perpendicular) is the component of the particles velocity perpendicular to B, and (B) is the magnetic field strength.

A

F = q v perpendicular B

40
Q

Lorentz force on a wire:
(I) current through the wire
(L) length of wire
(B) magnetic field

A

F = I L B

41
Q

Paramagnetic materials that increase the magnetic field less than .1%

A

Uranium and platinum

42
Q
  • Diamagnetic materials

- decrease the magnetic field less than .1%

A

Bismuth, mercury, silver

43
Q

will align their electron loops with each other, even when no external magnetic field is present

A

ferromagnetic

ex: iron cobalt and nickel

44
Q

Amperes law for a long straight wire says the magnitude of the magnetic field strength produced by an infinitely long wire with current (I) inside is:

A

B = h I / r
(r) distance from the wire
(h) = 2x10^-7Tm/A
(I) current in wire.

45
Q

AC electric motors create:

A

a rotating magnetic field

46
Q

If a person winds a coil of wire around a steel rod, and then passes an electric current through the wire, then:

A

the steel rod becomes an electromagnet

47
Q

magnetic fields are generated by:

A

electrons at rest, permanent magnets, moving charges

48
Q

two wires with electric currents running parallel to each other experience:

A

a mutual attraction

49
Q

two wires running antiparallel to each other experience:

A

a mutual repulsion

50
Q

the force on a moving charge in the presence of a magnetic field is always

A

perpendicular to both the charges velocity and the magnetic field

51
Q

the force on a moving charge in the presence of a magnetic field is always proportional to:

A

the velocity of the charge

52
Q

the force on a moving charge parallel to a magnetic field is always

A

0

53
Q

the force on a charge (q) moving with velocity (v) perpendicular to a magnetic field (B) is given by:

A

F = q v = B

54
Q

two kinds of the same magnetic pole

A

repel each other

55
Q

two kinds of the opposite magnetic pole

A

attract each other

Physics (3 decks)

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