12th of may learn em

Question 1

is magnetic flux density?

Answer 1

strength of a magnetic field

Question 2

unit of magnetic flx density

Answer 2

tesla

Question 3

tesla definition

Answer 3

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

Question 4

what is the symbol for magnietic flux density

Answer 4

B

Question 5

whats a couple

Answer 5

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

Question 6

whats a torque

Answer 6

the moment of a coupe

Question 7

equation for torque

Answer 7

one of the forces X perpendicular distance between forces

Question 8

equations for upthrust

Answer 8

upthrust =Axpg (Ax is volume of water displaced)

Question 9

Archimedes principle

Answer 9

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

Question 10

whats the ultimate tensile strength

Answer 10

maximum stress a material can withstand before it breaks

Question 11

whats a semiconductor

Answer 11

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

Question 12

what is intensity proportional to

Answer 12

amplitude squared

Question 13

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

Answer 13

P/4pi r^2

Question 14

conditions for TiR

Answer 14

• 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

Question 15

electronvolt definition

Answer 15

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

Question 16

equation to find plancks constant

Answer 16

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

Question 17

whats the work function

Answer 17

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

Question 18

how to find the threshold frequency

Answer 18

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

Question 19

specific heat capacity definition

Answer 19

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

Question 20

whats specific latent heat?

Answer 20

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

Question 21

what is free oscillation

Answer 21

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

Question 22

what is natural frequency

Answer 22

the frequency of the free oscillations of the oscillator

Question 23

what is driving frequency

Answer 23

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

Question 24

when will something resonate

Answer 24

when the driving frequency is equal to the natural frequency

Question 25

what is resonance

Answer 25

where the amplitude of oscillations increase dramatically, without being damped the system will break

Question 26

uses of resonance

Answer 26

musical instruments. MRI scans

Question 27

what is newtons law of gravitation

Answer 27

the force between two point masses is directly proportional to the product of masses and inversely proportional to the square of their separation

Question 28

boyles law

Answer 28

pressure is inversely proportional to volume

Question 29

pressure law

Answer 29

pressure is proportional to temperature

Question 30

whats an isochronus oscillator

Answer 30

an oscillator that has the same period regardless of amplitude

Question 31

difference between displacement equations for shm

Answer 31

Acoswt is when the thing starts with a positive displacement
Asinwt is when it starts with zero displacement

Question 32

keplers first law

Answer 32

orbit of planet is elliptical with the sun at one of two foci

Question 33

what does this equation relate to? g=-GM/r^2

Answer 33

for an object r distance away from the centre of an object with mass M

Question 34

what does this equation relate to? F=-GMm/r^2

Answer 34

force between two objects with masses M and m separated by distance r

Question 35

keplers second law

Answer 35

line segment joining planet and sun will sweep out equal areas during equal intervals of time

Question 36

keplers third law

Answer 36

Time period squared is proportional to r cubed. where r is average distance from sun

Question 37

what is gravitational potential

Answer 37

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

Question 38

what is gravitational potential energy

Answer 38

the capacity for doing work as a result of an objects position in a gravitational field

Question 39

what is considered a low mass star

Answer 39

0.5-1 solar masses

Question 40

what is considered a high mass star

Answer 40

> 1 solar masses

Question 41

what is considered very very high mass star

Answer 41

> 3 solar masses

Question 42

what is the Chandrasekhar limit?

Answer 42

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

Question 43

how to work out a parsec

Answer 43

1AU/tan(1/3600)

Question 44

whats the cosmological principle

Answer 44

assumes the universe is isotropic and homogenous and the laws of physics are universal

Question 45

what does isotropic mean

Answer 45

looks the same in all directions

Question 46

what does homogenous means

Answer 46

matter is distributed uniformly