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