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physics > topic 7 > Flashcards

topic 7 Flashcards

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1
Q

what is an electric field

A

a region where a charged particle experiences a force

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2
Q

electric field strength formula

A

E = F / Q

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3
Q

define electric field strength

A

force per unit charge experienced by an object in an electric field

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4
Q

electric field strength in uniform and radial field

A
  • uniform - E is constant
  • radial - E varies
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5
Q

Coulomb’s law

A
  • the magnitude of the force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them
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6
Q

Coulomb’s law formula

A

F = Q1Q2 / 4πε0r^2

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7
Q

what makes the force repulsive?

A
  • if charges have the same sign
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8
Q

what makes a force attractive?

A
  • if charges are oppositely signed
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9
Q

what do point charges form

A

a radial field

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10
Q

electric field strength in a radial field formula

A

E = Q / 4πε0r^2

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11
Q

absolute potential energy

A
  • the potential energy per unit charge at a positive point charge at that point in the field
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12
Q

at which point is the absolute magnitude of electric potential the highest?

A
  • at the surface of the charge
  • as distance from charge increases, potential decreases
  • hence, electric potential at infinity is zero
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13
Q

positive charge - what is potential?

A
  • potential is positive
  • charge is repulsive
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14
Q

negative charge - what is potential?

A
  • potential is negative
  • charge is attractive
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15
Q

how can you form an electric field

A
  • two parallel plates
  • potential difference across them
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16
Q

how to calculate electric field strength formed between the plates

A

E = V / d
- V is the p.d. across the plates
- d is the distance between the two plates

17
Q

electric potential in a radial field

A

V = Q / 4πε0r^2

18
Q

what is electric potential difference

A
  • the energy needed to move a unit charge between two points
19
Q

what do the field lines show

A
  • the direction of force acting on a positive charge
20
Q

field lines - uniform vs radial

A
  • uniform - same electric force is exerted everywhere (equally spaced parallel lines)
  • radial - depends on the distance between the two charges
21
Q

what does the distance between the field lines represent

A

the magnitude of the force

22
Q

what surfaces to electric fields have

A

equipotential surfaces

23
Q

what happens when a charge moves along an equipotential surface

A
  • no work is done
  • this is because the potential on an equipotential surface is the same everywhere
24
Q

magnetic flux denisty

A

measure of the strength of the field

25
Q

magnetic flux linkage

A

magnetic flux multiplied by the number of turns in a coil

26
Q

Flehming’s left hand rule - charged particles

A
  • thumb - direction of motion/force
  • first finger - direction of field
  • second finger - direction of conventional current
27
Q

what direction is the force

A
  • force is always perpendicular to the motion of travel
  • hence charged particles travel in a circular motion in magnetic fields
28
Q

calculating force on a charged particle

A

F = Bqv sinθ

29
Q

Flehming’s left hand rule - current carrying conductors in a magnetic field

A
  • motion
  • field
  • current
30
Q

what happens when a current passes through a wire

A
  • a magnetic field is induced
  • field lines of induced magnetic field form concentric rings around the wire
31
Q

calculating magnitude of force on the wire

A

F = BIl sinθ

32
Q

how is an emf induced in a coil

A
  • conducting rod moves relative to magnetic field
  • electrons in rod experience a force
  • build up of electrons on one side of the rod
  • e.m.f. is induced
33
Q

when is a current induced

A
  • if the coil forms a complete circuit a current is induced
34
Q

Lenz’s law

A

direction of induced current is such as to oppose the motion causing it

35
Q

induction of emf in a coil through the change in current of another coil

A
  • magnetic field is induced around a coil current-carrying wire
  • if the current through the wire changes, magnetic field will also change
  • emf will be induced in a second coil
  • induced emf in the second coil is proportional to the change in current in the first coil
  • if second coil completes a full circuit, a current is also induced
36
Q

factors affecting the emf induced in the second

A
  • magnetic flux density
  • distance between the two coils
  • number of turns in the second coil
  • cross-sectional area of second coil
  • time taken for change in current

physics (9 decks)

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