1
Q
what must be specified when describing a field
A
- the type of field
- the property the object must have in order to be influenced by the field
- the property which has given rise to the field
2
Q
what are the 3 types of fields
A
- gravitational fields
- electric fields
- magnetic fields
3
Q
what are the two main types of fields
A
- radial fields
- uniform fields
4
Q
what is a uniform field
A
a field where the field strength is the same at all points
5
Q
what is a gravitational field
A
the force between two object of mass
6
Q
what is newtons law of gravitation
A
the mutually attractive force experienced by two objects with mass is
- directly proportional to the product of their masses
- inversely proportional to the square of their separation
7
Q
what is gravitational field strength
A
the force per unit mass which will act on a point mass placed at that point
8
Q
what is the lagrange point
A
the exact point between 2 object where there is no resultant gravitational field.
9
Q
what is gravitational potential energy
A
the energy an object has when lifted off the ground
10
Q
what is GPE outside the earths surface
A
the energy an object possess due to its position in a gravitational field
11
Q
what is gravitational potential at a point in a gravitational field
A
the work which must be done per unit mass to move a point mass from infinity to that point
12
Q
what does gravitational potential depend on
A
- the mass of the object
- the distance the point is from that mass
13
Q
what does orbital velocity depend on
A
the mass of the sun and the mean radius of the planet
14
Q
what is Keplers third law
A
the square of the orbit at period of a planet is directly proportional to the cube of the planets distance from the sun
15
Q
what are the two types of satellites orbiting earth
A
geostationary satellites
polar satellites
16
Q
what is a geosynchronous orbit
A
an orbit which appears to be stationary
17
Q
characteristics of geostationary satellites
A
- have a geosynchronous orbit
- are always above the same position on the earths surface
- orbit in the same direction as the earths rotation
- are used for communication
18
Q
characteristics of polar satellites
A
- orbit perpendicular to the equatorial plane
- orbit earth at a much lower altitude
- used for weather monitoring and military applications
19
Q
what is the total energy required to place a satellite in orbit around the earth
A
gravitational potential energy to place the satellite in the position in the earths gravitational field
plus
the kinetic energy of the satellite once its orbiting
20
Q
what is an electric field
A
a region where a charged particle experiences a force
21
Q
what does coulomb’s law state
A
that the electrical force between two charged objects is directly proportional to the square of the separation
22
Q
what is electric field strength
A
the force per unit charge acting on a charge in an electric field
23
Q
what is the units of electric field strength
A
NC-1
24
Q
is electric field strength vector or scalar
A
vector
25
how do you calculate resultant E with opposite charges
you add the values
Et= E1 + E2
26
how do you calculate resultant E with like charges
you subtract the individual charges
Et= E1- E2
27
how are uniform electric fields created
created in between parallel plates
28
what does electric field strength depend on
- the p.d between the plates
- the distance between the 2 plates
29
what is the unit of field strength
Vm-1
30
what is field strength equation
E = V / d
31
what is the formula for work done in a uniform electric field
w = q △V
32
how do you calculate changes in Ep
1. calculate the values of F using coloumbs law equation in the range covering r1 and r2
2. plot a graph of F against r:
3. work out the area under the graph
33
what is electric potential
this is the work done per coulomb in moving a positive test charge from infinity to that point in the field
34
what is potential difference
this is the work done per coulomb from moving a positive test charge between 2 points in a field
35
what is potential at infinity
0
36
what happens to potential as you move a positive test charge away from a positive field
it decreases
37
what happens to potential as we move a positive test charge to a negative field
it decreases
38
what happens to potential as you move a positive test charge away from a positive field
it decreases
39
what happens to potential as we move a positive test charge towards a positive field or away from a negative field
it increases
40
what is potential gradient in unifrom fields
the change of potential per unit charge of distance in a given direction
41
why is it difficult to measure the value of alternating p.d or current
because its value changes from one instant to another
42
what is the definition of root mean square speed for alternating current
the value of an alternating current that is equal to the value of direct current that would give the same heating effect
43
what is the time base setting in an oscilloscope
a setting to vary the frequency of a wave/ period
44
what is the Y-gain on an oscilloscope
it is used to vary amplitude
45
how do you calculate peak p.d using an oscilloscope
* the y-gain gives the value of each vertical square on the screen
* to obtain the peak p.d, multiply the number of squares by the y-gain
46
how do you calculate the frequency using an oscilloscope
* the time base will give time per division
* to obtain the period, multiply the number of squares by the time base
47
what is a capacitor
an electrical component which can store and then release an electrical charge
48
what are capacitors used for
used to store energy in electronic circuits, commonly for a backup release of energy is the power fails
49
what is a dielectric
an insulating material placed between the two plates to increase capacitance
50
how does a dielectric increase capacitance
by ensuring charge does not freely flow between the plates
51
what is the symbol of a capacitor
——| |——
52
what is the definition of capacitance
the charge stored per unit potential difference between the plates
53
what is the total capacitance of capacitors in series
1/C = 1/C1 + 1/C2 + 1/C3
54
What is the total capacitance of of capacitors in parallel
C = C1 + C2 + C3
55
what factors affect capacitance
- plate separation - greater distance between plates the less effect they have on eachother, so the capacitance is reduced
- surface area - the greater the area of overlap of the plates the more charge that can be stored for a particular voltage
- permittivity - how easy it is to generate an electric field in a certain material
56
what is the relative permittivity of a dielectric
its the factor by which the electric field between the plates will decrease
57
58
what is a magnetic field
a region in which a moving charge, a current carrying conductor, a magnetic material and a magnet can all experience a force
59
in which direction do the magnetic lines of flux move
North to south
60
how do you work out the direction of a field in a straight current carrying wire
you use the right hand grip rule
61
what is a solenoid
a core wrapped by many could of wire
62
how do you increase the field strength of a solenoid
increasing the current
adding more turns of coil
decreasing the gaps between coils
using an iron core (strongest magnetic material)
63
what is the motor effect
the force experienced by a current carrying conductor placed in a magnetic field, caused by the wires own magnetic field and the external field, causing motion of deflection
64
what is magnetic flux density
a measure of the number of field lines per unit area
65
how do you determine direction of a force in a magnetic field
using flemings left had rule
66
in flemings left hand rule what is
-the thumb
- first finger
-second finger
thumb- direction of thrust (F)
first finger- direction of field
second finger- direction of current
67
what does a DC motor consist of
coils of wire which spins in between the poles of 2 magnets
68
how does a DC motor work
when a current is flowing through the wire a couple is created and the coil spins by half a turn. the split ring commutator reverses the current direction every half a turn, ensuring that the coils of wire continue to spin in the same direction
69
what is the equation for force on a moving charge
F= BQV
70
what is the equation for force on a moving charge if the particle is an electron or positron
F= BeV
71
what happens to a particle moving fast enough in a magnetic field
the particle would travel in circular motion within the field
72
what is the negation for a force due to a magnetic field which causes a centripetal force on the particle
r= mv/ BQ
73
What is a cyclotron
a particle accelerator
74
How does a cyclotron work
- a strong magnetic field is applied perpendicular to the D’s which forces charged particles to move in a circular path inside the D’s
- the particles gain EK when they travel across the gap and accelerate towards the next D
- the alternating P.D is timed to change direction every time the particles reach the gap between the D’s, so the particles will continuously accelerate
75
why is the speed in a cyclotron limited
due to special relativity
76
what is special relativity
as the particles approach c, they get progressively more massive and the time spent in each D increases, meaning that they start to get out of step with the alternating P.D.
77
how does a synchroton overcome the problem of special relativity
by increasing the flux density as the speed of the particles increases, : . keeping the radius constant
78
what is electromagnetic induction
when a wire is moved into a magnetic field, an e.m.f is produced which will lead to the flow of electrical current
79
what is Faradays law of induction
the magnitude of the induced e.m.f. is equal to the rate of change of flux linkage
80
how can you increase the induced e.m.f. in electromagnetic induction
- using a stronger magnet
- using a coil with a greater number of turns
- using a coil with a greater cross-sectional area
- increasing the relative velocity
81
what can we use Lenz’s law for
to determine the direction of an induced e.m.f
82
what is Lenz’s law
it states that the direction of the current induced in a conductor by a changing magnetic field is such that the magnetic field created by the induced current opposes the initial changing magnetic field
83
what happens when a wire cuts flux lines
it creates flux linkage
84
what happens when a coil rotates in a magnetic field
an alternating e.m.f is induced in the coil
85
what do you get when a coil rotates with constant angular velocity in a uniform magnetic field
you get a sinusoidal alternating e.m.f (sinusoidal graph)
86
when do the maximum/ minimum values of e.m.f occur with a coil rotating in a uniform magnetic field
maximum = when the coil is parallel to the field
minimum = when the coil is perpendicular to the field
87
What type of graph do you get with the equation of flux linkage
a cos graph
88
what do transformers do
they are used with alternating currents to change the size of their voltage
89
what is a transformer made of
a primary coil, attached to an input voltage and a secondary coils connected to the output voltage and an iron core
90
what can we deduce about transformers using Faradays law
that the ratio of their voltage in the primary coil to the secondary coild, is the same as the ratio of the number of turn on the primary coil to the secondary coil
91
what are the two types of transformers
- step-up transformers
- step down transformers
92
what do step-up transformers do
they increase the input voltage by having more turns on the secondary
93
what do step-down transformers do
they decrease the input voltage by having less turns on the secondary coil
94
what are the causes of energy loss in transformers
- Eddy currents
- resistance in the coils
- if the core is not easily magnetized
95
what is eddy currents and how can you reduce the effect
- they are induced by the alternating magnetic field in the primary coil and form a loop. this loop opposes the field that produced them, reducing the fields flux density and they generate heat. causing energy to be lost
- using a laminated iron core (prevents the eddy currents from passing through the insulation and so their amplitude is reduced)
96
how can you reduce resistance in the coils in transformers
use a thick wire/ low resistance wire
97
how do you prevent energy from being lost due to the core not being easily magnetised in transformers
- use a soft iron core
a-level physics
flashcards
Decks in class (14)
# Cards
-
3- quantum phenomena49
-
11- materials28
-
6+7 forces in equilibrium + on the move18
-
Waves and optics89
-
8- newtons laws of motion6
-
9- forces and momentum10
-
10- work, energy and power10
-
circular motion10
-
19- thermal physics19
-
18- simple harmonic motion27
-
fields97
-
20- gases22
-
nuclear physics31
-
turning points27
