Quanta and Waves

Question 1

What is black body radiation?

Answer 1

a surface that absorbs all wavelengths of radiation and also emits all wavelengths of radiation eg the sun. This can be described as λmaxT=constant

Question 2

What is the photoelectric formula?

Answer 2

c=fλ and E=hf

E=hc/λ

The kinetic energy of an electron can be found with E=hf-hf0

Question 3

What is the de broglie wavelength formula and derivation?

Answer 3

E=mc^2 and E=hc/λ

mc^2=hc/λ
mc=h/λ
p=h/λ

This is evidence for wave particle duality as it links a property for waves with a property for particles

Question 4

What is the bhor model of hydrogen?

Answer 4

• electrons orbit the nucleus in discreet energy levels
• these orbits must exist as a multiple of h/2pi
• the angular momentum can be found using L=nh/2pi

Question 5

What will happen if the de broglie wavelength of a large mass is calculated?

Answer 5

the wavelength will be very small. the wavelength would be too small to exhibit diffraction so therefore the mass cannot be considered a wave as well as a particle

Question 6

What is the heisenburg uncertainty principle and the formulae?

Answer 6

you cannot know both the exact position and velocity of a mass with precise accuracy at the same time

ΔEΔt>h/4pi

ΔxΔp>h/4pi

Question 7

What is quantum tunneling?

Answer 7

an small object trapped on one side of a barrier can appear on the other side of the barrier due to the uncertainty principle eg an electron behind a nucleus.

this is evidence of wave particle duality

Question 8

What are cosmic rays?

Answer 8

high energy particles arriving at earth which have originated elsewhere. they mainly consist of protons

they originate from the sun if low energy
they originate from elsewhere in the milkyway if intermediate energy
their origin is still to be determined if it is an ultra high energy cosmic ray

Question 9

How are electron volts calculated?

Answer 9

Ew=QV

where the charge (Q) is 1 and voltage (V) is the amount of volts being used

Question 10

How are the northern lights created?

Answer 10

When charged particles enter the atmosphere, electrons become excited and enter a higher orbit due to colliding with cosmic rays. The electrons emit a photon when the elctrons goes back to the original orbit. The photon is the northern lights.

Question 11

How is the force experienced by a charged particle in a magnetic field calculated?

Answer 11

F=BQvsinθ

The direction of the force can be found with the right hand rule

Question 12

How is the radius of the orbit of a charged particle calculated?

Answer 12

F=mv^2/r and F=BQsinθ

mv^2/r = BQv

r=mv/BQ

Question 13

Why does a charged particle follow a helical path when in a magnetic field?

Answer 13

When the velocity is split up into its parallel and perpendicular vectors:

the perpendicular vector causes a central force and hence produces a circular orbit. v=vsinθ

the parallel vector causes no magnetic force, causing a constant velocity parallel to the field. v=vcosθ

Question 14

What is solar wind?

Answer 14

the sun produces a stream of charged particles due to high temperature

the heat energy provides kinetic energy to the particles which allows them to overcome the gravitational field of the sun

it is made up of protons and electrons

solar wind distorts earths magnetic field

earths magnetic field protects us from solar wind by directing it around earth

Question 15

What is simple harmonic motion?

Answer 15

where an object oscillates around an equilibrium position and its acceleration is proportional to the displacement.

energy continually changed from Ep to Ek until an equilibrium is reached

This can be stated with F=-ky

Question 16

What is the equation for simple harmonic motion?

Answer 16

a = -ω^2y

ω=2πf

y=Asin(ωt) which can be differentiated twice to get the first equation (when y=0 and t=0. if y=A and t=0 use cos)

v=±ω(A^2-y^2)^1/2

Question 17

What is damping?

Answer 17

damping is where in a shm system, friction will decrease the amplitude of the oscillations over time

Question 18

What is a travelling wave and its formula?

Answer 18

through a waves motion, energy is transferred from one position to another with no transfer of mass

y=Asin2π(ft-x/λ)

energy is proportional to kA^2

Question 19

What is the formula for phase difference?

Answer 19

ϕ=2πx/λ measured in radians

Question 20

What is a stationary wave?

Answer 20

a wave that is in a fixed position so oscillates in places and bounces back on itself. Constructive and destructive interference takes place. Constructive interference creates antinodes and destructive interference creates nodes.

Question 21

What are the requirements for waves to be coherent?

Answer 21

constant phase difference

come from same source