# 12th of may learn em Flashcards Preview

## Physics ALevel OCR > 12th of may learn em > Flashcards

Flashcards in 12th of may learn em Deck (46)
1
Q

is magnetic flux density?

A

strength of a magnetic field

2
Q

unit of magnetic flx density

A

tesla

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

4
Q

what is the symbol for magnietic flux density

A

B

5
Q

whats a couple

A

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

6
Q

whats a torque

A

the moment of a coupe

7
Q

equation for torque

A

one of the forces X perpendicular distance between forces

8
Q

equations for upthrust

A

upthrust =Axpg (Ax is volume of water displaced)

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

10
Q

whats the ultimate tensile strength

A

maximum stress a material can withstand before it breaks

11
Q

whats a semiconductor

A

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

12
Q

what is intensity proportional to

A

amplitude squared

13
Q

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

A

P/4pi r^2

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
15
Q

electronvolt definition

A

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

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

17
Q

whats the work function

A

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

18
Q

how to find the threshold frequency

A

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

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
Q

what is resonance

A

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

26
Q

uses of resonance

A

musical instruments. MRI scans

27
Q

what is newtons law of gravitation

A

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

28
Q

boyles law

A

pressure is inversely proportional to volume

29
Q

pressure law

A

pressure is proportional to temperature

30
Q

whats an isochronus oscillator

A

an oscillator that has the same period regardless of amplitude

31
Q

difference between displacement equations for shm

A

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

32
Q

keplers first law

A

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

33
Q

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

A

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

34
Q

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

A

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

35
Q

keplers second law

A

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

36
Q

keplers third law

A

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

37
Q

what is gravitational potential

A

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
Q

what is gravitational potential energy

A

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

39
Q

what is considered a low mass star

A

0.5-1 solar masses

40
Q

what is considered a high mass star

A

> 1 solar masses

41
Q

what is considered very very high mass star

A

> 3 solar masses

42
Q

what is the Chandrasekhar limit?

A

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
Q

how to work out a parsec

A

1AU/tan(1/3600)

44
Q

whats the cosmological principle

A

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

45
Q

what does isotropic mean

A

looks the same in all directions

46
Q

what does homogenous means

A

matter is distributed uniformly