Week 1 biochem - Electromagnetic radiation

Question 1

what form is energy and where is it stored

Answer 1

energy is in waveform
the energy is stored in electric and magnetic fields

Question 2

what is wavelength and frequency measured in

Answer 2

wavelength is measured in meters
frequency is measured in waves/second

Question 3

what is the formula for energy

Answer 3

E= h x v
where h is planks constant

Question 4

how are wavelength, frequency and energy linked

Answer 4

Long wavelength =
low frequency =
low energy

short-wavelength =
high frequency =
high energy

Question 5

what is the energy associated with

Answer 5

• energy associated with electrons
• energy associated with vibrations between atoms
• energy associated with rotations of atoms relative to other electrons

Question 6

what are definite packets for energy levels called

Answer 6

energy levels are in definite packets called quanta
energy in electromagnetic radiation is also in definite packets called photons

Question 7

what happens when EM radiations strike a molecule changes its energy level

Answer 7

• electrons transition to a higher energy level - the level depends on the wavelength(s) of the absorbed EM
  -electron return to the ground state by emitting photos of EM radiation at lower energy, and hence longer wavelength(s)

Question 8

what is the difference between absorbed wavelength and emitted wavelength called

Answer 8

the strokes shift

Question 9

what causes the difference in energy

Answer 9

when heat emits

Question 10

what is the definition of an electron

Answer 10

the flow of electric charge

Question 11

what is the definition of energy current

Answer 11

the flow of electrons (negative) or rarely (positive) ions

Question 12

what is the definition of potential difference (PD) or voltage

Answer 12

it is work done per unit of charge when charge is moved between 2 points in an electric field. it is measured in volts
current will flow when there is a potential difference between 2 points in an electric field

Question 13

how is potential difference (PD) and power supply linked

Answer 13

when the power supply is disconnected, then there is no PD between the electrodes
when the power supply is connected, then PD is created between electrodes
when PD is present then charged particles will flow between electrodes

Question 14

what is the dual nature of light

Answer 14

everything in the universe from light to electrons to atoms behaves both like a particle and wave at the same time

Question 15

what was Plank’s idea and how did Einstien apply his idea to light

Answer 15

Plank explained objects made up of oscillators could only emit light in discrete chunk units of energy that depend on the frequency of light.
Einstein said that light, which everybody knew was a wave, is really a stream of photons, each with a discrete amount of energy. this explains the way light shining on metal surfaces knocks loose electrons

Question 16

who is Ernest Rutherford and what was his idea

Answer 16

in 1909 in England, Ernest Marsden and Hans Geiger working for Rutherford shot alpha particles at gold atoms and were stunned to find some bounced straight backwards.
this showed that most of the mass of the atom is concentrated in a tiny nucleus.

however the problem with the Rutherford atom is it can’t work,
classical physics tells us that an electron whipping around a circle emits light and we can use this to generate radio waves and x-rays.
Rutherford atom should spray x-rays in all directions for a brief instant before the electron spirals in, to crash into the nucleus.

Question 17

who is Niels Bohr and what was his idea

Answer 17

He is a Danish theoretical physicist
he proposed that electrons in certain special orbits don’t emit any light at all. Atoms absorb and emit light only when electrons change orbits and the frequency of light depends on the energy difference (in just the way Plank and Einstien introduced it).
Bohr’s atom fixes Rutherford’s atom and explains why atoms only emit specific colours of light.
each element has its own special orbit and thus its own unique set of frequencies. however, the problem with Bohr’s atom is there is no reason for those orbits to be special.

Question 18

Who is Louis de Broglie and what was his idea

Answer 18

He is a French PhD student
he pointed out that if the light which everyone knew was a wave behaves as a particle, maybe the electron which everyone knew is a particle behaves like a wave. (if electrons are waves, it’s easy to explain Bohr’s rule for picking out special orbits.)
nowadays there is a clear demonstration of this:
shooting single electrons at a barrier with slits cut into it.
each electron is detected at a specific place at a specific time like a particle.
but when you repeat the experiment many times all the individual electrons trace out a pattern of stripes characteristic of wave behaviour.

Question 19

what happens when to take a flashlight and shine it towards a prism and then put hydrogen in the pathway

Answer 19

if you take a flashlight and shine it towards a prism, the white light would split up into different colours, each colour is on a different beam.
if you put hydrogen in the pathway, the light passes through the hydrogen gas and when it splits up certain colours are missing.
some colours are missing because the hydrogen absorbs certain colours and the remaining colours shine through the pyramid.

Question 20

what is a photon and what is its energy

Answer 20

experiments have shown light sometimes acts as particles, so instead of continuous waves, light is composed of a tone of tiny little particles called photons.
the energy you see in a photon depends on the frequency of the light thus the energy depends on the colour of the light.
every single photon has an energy equal to Plank’s constant x the photon’s frequency.

Question 21

how are energy and frequency linked

Answer 21

when frequency decreases, the energy decreases as well.
this is because energy is equal to Plank’s constant x frequency.

Question 22

what is voltage

Answer 22

electricity is the flow of free electrons between atoms. voltage is what pushes electrons around a circuit, without voltage, electrons would move randomly in any direction.
thus only when we apply voltage to a circuit is when all the free electrons with move in the same direction causing current.

Question 23

how are voltage and current linked

Answer 23

the more voltage we have, the more current can flow

Question 24

how are voltage and potential difference linked

Answer 24

voltage can be referred to as potential difference, this means how much work can be potentially done by a circuit.
example
if we have a 1.5v battery, the battery has a potential difference of 1.5v between its negative and positive terminal.
if we connect a piece of wire to both terminals of the battery, then the pressure of a battery will force the electrons to flow all in the same direction along the same path.