12th of may learn em Flashcards
is magnetic flux density?
strength of a magnetic field
unit of magnetic flx density
tesla
tesla definition
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
what is the symbol for magnietic flux density
B
whats a couple
pair of forces that are equal, acting in opposite directions and parallel
whats a torque
the moment of a coupe
equation for torque
one of the forces X perpendicular distance between forces
equations for upthrust
upthrust =Axpg (Ax is volume of water displaced)
Archimedes principle
upthrust exerted on a body Immersed in fluid, partially or fully submerged, is equal to the weight of fluid displaced
whats the ultimate tensile strength
maximum stress a material can withstand before it breaks
whats a semiconductor
component with a negative temperature coefficient. resistance drops as temp increases
what is intensity proportional to
amplitude squared
whats the intensity of something with a radiant power spreading out in a sphere
P/4pi r^2
conditions for TiR
- 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
electronvolt definition
energy transferred to or from an electron when it is accelerate by a potential difference of 1 volt
equation to find plancks constant
use LEDs. plot graph of threshold voltage against 1/wavelength of light emitted. find gradient and do some maths
whats the work function
minimum energy required to emit an electron from the surface of a metal
how to find the threshold frequency
work function = hf0 because kinetic energy of emitted electron would be 0
specific heat capacity definition
energy required per unit mass to change the temperature of a substance by 1 kelvin
whats specific latent heat?
energy required to change the phase per unit mass whilst at a constant temperature
what is free oscillation
a system that is displaced and allowed to oscillate without any external force is free oscillation
what is natural frequency
the frequency of the free oscillations of the oscillator
what is driving frequency
the frequency an oscillator is made to oscillate at by a periodic driver
when will something resonate
when the driving frequency is equal to the natural frequency
what is resonance
where the amplitude of oscillations increase dramatically, without being damped the system will break
uses of resonance
musical instruments. MRI scans
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
boyles law
pressure is inversely proportional to volume
pressure law
pressure is proportional to temperature
whats an isochronus oscillator
an oscillator that has the same period regardless of amplitude
difference between displacement equations for shm
Acoswt is when the thing starts with a positive displacement
Asinwt is when it starts with zero displacement
keplers first law
orbit of planet is elliptical with the sun at one of two foci
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
what does this equation relate to? F=-GMm/r^2
force between two objects with masses M and m separated by distance r
keplers second law
line segment joining planet and sun will sweep out equal areas during equal intervals of time
keplers third law
Time period squared is proportional to r cubed. where r is average distance from sun
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
what is gravitational potential energy
the capacity for doing work as a result of an objects position in a gravitational field
what is considered a low mass star
0.5-1 solar masses
what is considered a high mass star
> 1 solar masses
what is considered very very high mass star
> 3 solar masses
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
how to work out a parsec
1AU/tan(1/3600)
whats the cosmological principle
assumes the universe is isotropic and homogenous and the laws of physics are universal
what does isotropic mean
looks the same in all directions
what does homogenous means
matter is distributed uniformly
