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Electromagnetism Flashcards

(61 cards)

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1
Q

what are the four non-contact force

A

strong nuclear force

weak nuclear force

electromagnetic force

gravitational force

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2
Q

what is a non-contact force

A

a non-contact force that can exert a force on an object without making any physical contact with it.

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3
Q

Is an Electric field a vector quantity or scalar quantity

A

vector quantity

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4
Q

how are electric field lines are drawn

A

Electric field lines are drawn with arrowhead indicating the direction of the force

a single positive charge particles will have the arrowheads pointing away from the particle

a single negative charge particle will have the arrowheads pointing towards the particle

for two of the same charge particles the arrow lines will diverge between the two charges

for to opposite charge particles the arrows will connect to each other (the arrows will pointing towards the negative particle)

for parallel oppositely charged plates the arrows are drawn from the positive plate to the negative plate.

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5
Q

which direction will a proton experience a force in a electric field

A

it will experience a force in the same direction as the field (towards the negative plate)

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6
Q

which direction will a electron experience a force in a electric field

A

it will experience a force in the opposite direction to the electric field (towards the positive plate)

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7
Q

what is the Electric field strength

A

the Electric field strength is the force applied per coulomb of charge

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8
Q

what is the equation of the Force on a charged particle

A

F = qE

F is the force on the charged particle (N)

q is the charge of the object experience the force (C)

E is the strength of the electric field (NC^-1)

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9
Q

Does Newton’s second law of motion F(net) = ma relate to the formula to calculate the force on a charge particle

A

yes

F=ma is also equal to F = qe

ma = qE

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10
Q

What is the Electrical potential (V)

A

the Electric potetnial (also known Electrical potential energy) is defined as the work required per unit charge to move a positive point charge from infinity to a place in the electric field.

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11
Q

what is the formula for the work done in an electric field

A

W = qV

W is the work done on a positive point charge or on the field(J)

q is the charge of the point charge(C)

V is the electrical potential (JC^-1) or volts (V)

or

W = qED

E is the magnitude of the electrical field strength (Vm^-1 or NC^-1)

d is the distance between points, parallel to the field (m)

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12
Q

What is the electrical potential difference

A

the electrical potential difference is the difference in potential between the positive plate and the negative plate

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13
Q

What is the formula for the Electric field strength

A

E = V/D

E is the electric field strenght (Vm^-1)

V is the potential difference (V)

d is the distance (m)

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14
Q

is the change in Kinetic energy energy equal to the work

A

yes

K = W

1/2 m v^2 = q V

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15
Q

What is Lorentze Force

A

It is the magintude of the force proportional to the strength of the magnetic field (B), the velocity of the charge particle and the angle the object is moving with respect to the magnetic field. The force is at maxmium when the particle is moving at right angles to the field and has no force when the particle is travelling parallel to the magnetic field

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16
Q

What is the formula for Lorentz Force

A

F = qvB sin (angle)

F is the force (N)

q is the electric charge on the particle (C)

v is the instantaneous velocity of the particle(ms ^-1)

B is the strength of the magnetic field (T)

(angle) is the angle of the object moving at with respect to the magnetic field.

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17
Q

how do you use the right hand rule

A

the thumb is used to point in the direction of the velocity

the palm is the direction of the force

the fingers are the direction of the magnetic field.

if the force is on a negatively charged particle it will be in the opposite direction to that of an postively charged particle.

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18
Q

what do the dots depict in a field

A

dots are used to represent out of the page

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19
Q

what do the crosses describe in a field

A

the crosses are used to represent into the page

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20
Q

Is the magnitude of the net force F = ma equivalent to the magentic force on a charged particle F = qvB sin(angle)

A

yes

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21
Q

what is the formula for the force on a conductor

A

F = LIBsin (angle)

F is the force on the conductor (N)

L is the length of the conductor (m)

I is the current in the conductor (A)

B is the strength of the magnetic field (T)

(angle) is the angle between the magnetic field and the conductor.

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22
Q

what is the formula for the Magnetic Field strength

A

B = u(o)I/2(pi)r

B is the magnetic field strength (T)

u(o) is the magnetic permeability of free space

I is the current (A)

r is the radius from the current-carrying conductor to the location where the magnetic field is measured

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23
Q

is the force between two current-carrying conductors equal

A

Yes, this is beacuase of newton’s third law. The force between two parrallel conductors is equal and opposite.

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24
Q

what is the formula for the force per unit length between two current-carrying conductors

A

F/L = ( U(o) x I(1) x I(2) )/ 2(Pi)r

F/L is the force per unit length between conductors (Nm^-1)

U(o) is the magnetic permeability of free space

I(1) is the current conductor 1 (A)

I(2) is the current conductor 2 (A)

r is the distance between the two conductors (m)

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25
What is the Ampere (for a force between two current-carrying conductors)
The ampere is defined as being equal to the amount of current through two identical parrallel conductors of infinite length where they are 1m apart in order to produce a force unit length of 2 x 10^-7 Nm^-1 F/L = 2 x 10^-7 Nm^-1 r = 1m
26
can the equation for the forces between two parallel current-carrying conducts be used to derive the SI definition of the ampere
yes
27
If two parallel conductors carry current in the same direction is the force attractive or repulsive
attractive
28
if two parallel conductors carry current in the opposite direction is the force attractive or repulsive
repulsive.
29
what is an electromagnetic induction
it is the creation of an electric current in a conductor due to a change in the magnetic field acting on that conductor.
30
what is an emf
known as the electromotive force, it is a voltage or poetntial difference rather than a force.
31
what are the four types of changes in an electric field due to the induction of an emf
when the wire is moved down a current is induced that flows in the opposite direction of the magnetic field when the wire is held still there is no emf induction and no current when the wire is moved up a current is induced in the direction the same direction as the magnetic field when the wire is moved parallel to the field there is no current of emf incuded.
32
what is a magnetic flux.
The amount of the magnetic field is refered as the magentic flux, which is a scalar quantity. It can be interepeted as how many lines of force pass through a particular area
33
why is the magentic field strength also reffered to as the magnetic flux density
Because a strong magnetc field active over a small area can produce the same amount of magnetic flux as a weaker field acting over a larger area.
34
when is the magnetic flux at a maximum
it is a a maximum when the area vector is parallel to the magnetic field
35
when is the magnetic flux at zero
when the area vector is perpendicular to the magnetic field
36
what is the formula for the magentic flux
(0) = BA cos (angle) (o) is the magnetic flux. the unit for magnetic flux is the weber, abbreviated to Wb where 1 Wb = 1 Tm^-2 B is the strength of the magnetic field A is the area vector (m^2) (Angle) is the angle where the magnetic field is to the area vector
37
What Is Faraday's law of induction
The average emf induced in a conducting loop, in which there is a changing magnetic flux, is proportional to the rate of change of flux.
38
what is the formula for Farady's law of induction
E = -N (change in magnetic flux) / (Change in time) E is the induced emf (V) N is the number of turns or loops (change in magnetic flux): (WB) (change in time): (S) the negative sign in farady's law indicates the direction
39
what is Lenz's law
Lenz's law states that an induced emf always give rise to a current whose magnetic field will oppose the original change in flux.
40
Why is Lenz's law a necessary consequence of the law of conservation of energy
If lenz's law were not true then the new magnetic field created by a changing flux would encourage that change, which would have the effect of adding energy to the universe.
41
how to determine the induced current direction according to Lenz's law
what is the change that is happening? what will oppose the change and/or restore the original conditions what must be the current direction to match this opposition
42
What is a transformer
A transformer is a device for increasing and decreasing an alternating current (AC) voltage.
43
How does a Transformer work
A transformer works on the prinicple of a changing magnetic flux inducing an emf. A transformer consists of two coils known as primary and secondary coils. The changing flux originates with the alternating current supplied to the primary coil and the chaning magnetic flux is directed to the secondary coil where the changing flux will induce an emf in that coil.
43
Can Transformers work with with DC electrical supply
No
43
what is a DC voltage
also known as Direct current, a DC voltage has a constant unchanging current.
44
how to minimise eddy current losses
using insulated wires soft iron cores, laminiated.
44
what is an ideal transformer
an ideal transformer is the assumption that the transformer will be 100% efficient and energy losses can be ignored. However in a real transformer this assumption is a good approximation.
45
what is the transformer equation relating to the voltage and number of turns in each coil
Vp/Vs = Np/Ns or Vs/Vp = Ns/Np or Vp/Np = Vs/Ns Vp is primary coil voltage Vp is primary coil number of turns in each coil Vs is secondary coil voltage Vs is secondary coil number of turns in each coil
46
what is the difference between a step-up transformer and a step-down transformer
a step-up transformer increases the secondary voltage compared with the primary voltage. The secondary voltage is greater than the primary voltage and the number of turns in the secondary coil is higher than the number of turns in the primary coil. where as in a step-down transformer it decreases the secondary voltage with the primary voltage. the secondary voltage is less than the primary voltage and the number of turns in the secondary coil is less than the number of turns in the primary coil
47
what is the formula for power lost
P(loss) = (the change in)V x I or P(loss) = I^2 x R or P(loss) = (the change in) V^2 / R R is the resistance V is the voltage drop I is the current
47
what is the formula for the transformer equation in relation to the current and number of turns in each coil
Ip/Is = Ns/Np or Is/Ip = Np/Ns or Ip/Ns = Is/Np
48
what is the formula for torque in a motor
T = nIABsin(angle) T is the torque (N m) n is the number of coils I is the current(A) A is the area vector B is the strength of the magnetic Field (T) (angle) is the angle between the area vector and the magnetic field
49
what is a commutator usually made from
a split ring of coppper or another good conductor on which conducting brushes (ususually carbon blocks) rub.
50
what is an armature
the whole arrangement of the core and coils in a motor
51
what is a stator
are magnets in a motor that produce a magnetic field that are usually stationary, as distinct from the rotating rotor or aramarture.
52
How does an AC induction motor work
An Ac induction motor works by producing a rotating magnetic field.
53
what is eddy current breaking
also known as magnetic braking is where the electromagnetic force between a magnet and a conductor in motion is used to create the drag force.
54
what is an advantage of using an electromagnet for a braking system
the braking system can be turned on and off by adjusting the current in the electromagnet's windings.
55
what is an advantage and disadvantage of magnetic breaking
Advantage: Magnetic braking lacks the physical contact between components which makes for low maintenance and few replacement parts Disadvantage: when there is no motion between the magnet and conductor there is no static force to maintain the conduct at rest.
56
how does a coil in a simple DC motor rotate
it rotates because of the direction of the current, and hence the torque is reversed each half turn by the commutator.
57
what is a split ring commutator
a ring picking up the output from the coils has two breaks (or splits) in it at opposite sides of the ring. the direction of the output is changed by the commutator every half turn so that the output current is always in the same direction.

Physics (4 decks)

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