12th of may learn em Flashcards

(46 cards)

1
Q

is magnetic flux density?

A

strength of a magnetic field

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2
Q

unit of magnetic flx density

A

tesla

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3
Q

tesla definition

A

1 tesla is when a wire perpendicular to the field with a current of 1 amp experiences a force of 1 newton per metre of length

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4
Q

what is the symbol for magnietic flux density

A

B

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5
Q

whats a couple

A

pair of forces that are equal, acting in opposite directions and parallel

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6
Q

whats a torque

A

the moment of a coupe

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7
Q

equation for torque

A

one of the forces X perpendicular distance between forces

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8
Q

equations for upthrust

A

upthrust =Axpg (Ax is volume of water displaced)

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9
Q

Archimedes principle

A

upthrust exerted on a body Immersed in fluid, partially or fully submerged, is equal to the weight of fluid displaced

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10
Q

whats the ultimate tensile strength

A

maximum stress a material can withstand before it breaks

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11
Q

whats a semiconductor

A

component with a negative temperature coefficient. resistance drops as temp increases

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12
Q

what is intensity proportional to

A

amplitude squared

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13
Q

whats the intensity of something with a radiant power spreading out in a sphere

A

P/4pi r^2

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14
Q

conditions for TiR

A
  • light travelling in a medium with a higher refractive index and strike a boundary with a medium with a lower refractive index
  • angle it strikes at boundary must be bigger than the critical angle
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15
Q

electronvolt definition

A

energy transferred to or from an electron when it is accelerate by a potential difference of 1 volt

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16
Q

equation to find plancks constant

A

use LEDs. plot graph of threshold voltage against 1/wavelength of light emitted. find gradient and do some maths

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17
Q

whats the work function

A

minimum energy required to emit an electron from the surface of a metal

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18
Q

how to find the threshold frequency

A

work function = hf0 because kinetic energy of emitted electron would be 0

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19
Q

specific heat capacity definition

A

energy required per unit mass to change the temperature of a substance by 1 kelvin

20
Q

whats specific latent heat?

A

energy required to change the phase per unit mass whilst at a constant temperature

21
Q

what is free oscillation

A

a system that is displaced and allowed to oscillate without any external force is free oscillation

22
Q

what is natural frequency

A

the frequency of the free oscillations of the oscillator

23
Q

what is driving frequency

A

the frequency an oscillator is made to oscillate at by a periodic driver

24
Q

when will something resonate

A

when the driving frequency is equal to the natural frequency

25
what is resonance
where the amplitude of oscillations increase dramatically, without being damped the system will break
26
uses of resonance
musical instruments. MRI scans
27
what is newtons law of gravitation
the force between two point masses is directly proportional to the product of masses and inversely proportional to the square of their separation
28
boyles law
pressure is inversely proportional to volume
29
pressure law
pressure is proportional to temperature
30
whats an isochronus oscillator
an oscillator that has the same period regardless of amplitude
31
difference between displacement equations for shm
Acoswt is when the thing starts with a positive displacement Asinwt is when it starts with zero displacement
32
keplers first law
orbit of planet is elliptical with the sun at one of two foci
33
what does this equation relate to? g=-GM/r^2
for an object r distance away from the centre of an object with mass M
34
what does this equation relate to? F=-GMm/r^2
force between two objects with masses M and m separated by distance r
35
keplers second law
line segment joining planet and sun will sweep out equal areas during equal intervals of time
36
keplers third law
Time period squared is proportional to r cubed. where r is average distance from sun
37
what is gravitational potential
Vg at a point in a gravitational field is defined as the work done per unit mass to moved an object to that point from infinity
38
what is gravitational potential energy
the capacity for doing work as a result of an objects position in a gravitational field
39
what is considered a low mass star
0.5-1 solar masses
40
what is considered a high mass star
>1 solar masses
41
what is considered very very high mass star
>3 solar masses
42
what is the Chandrasekhar limit?
the mass of a stars core under which the electron degeneracy is sufficient to prevent collapsation due to gravity. value of 1.44 solar masses
43
how to work out a parsec
1AU/tan(1/3600)
44
whats the cosmological principle
assumes the universe is isotropic and homogenous and the laws of physics are universal
45
what does isotropic mean
looks the same in all directions
46
what does homogenous means
matter is distributed uniformly