5.D- Turning Points

Question 1

What were the 4 conclusions made about the charged particles moving in the discharge tube as a ‘cathode ray’

Answer 1

1. They were negatively charged
2. They had energy, momentum and mass
3. They are the same, no matter what gas is used or what the cathode is made of
4. They have a charge to mass ratio much higher than that of hydrogen ions (protons)

They would eventually be referred to as electrons.

Question 2

What was the significance of finding the specific charge of the electron

Answer 2

As this was now the highest specific charge ever recorded and was around 1800 times greater than the specific charge of H+ ions

Question 3

What is the significance of Millikan’s oil drop experiment

Answer 3

Millikan concluded that charge can never exist in smaller quantities than 1.6×10^-19C and that this is the charge carried by an electron (later experiments proved this to be true). Therefore charge is ‘Quantised’ in these packets.
Furthermore this allowed the mass of an electron to be calculated from it’s specific charge, making it the lightest particle ever discovered.

Question 4

Why was Huygen’s wave theory of light initially largely rejected?

Answer 4

1. They couldn’t measure the speed of light at the time so there was no way to tell who’s refraction model was correct
2. Newton had a much stronger reputation
3. Huygen’s wave theory considered it as longitudinal so couldn’t explain polarisation.

Question 5

What was the significance of Young’s double slit experiment

Answer 5

Young’s experiment was proof light could both diffract and interfere, strongly supporting Huygens’ wave theory.
Acceptance of Huygens’ theory however was still delayed due to Newton’s reputation and the issue of longitudinal waves not being able to be polarised. It wasn’t until The speed of light in water (the more optically dense medium) was proved to be slower than that in air, that people really started to believe Huygens.

Question 6

What are the five conclusions from the photoelectric effect

Answer 6

1. For a given metal, no photoelectrons are emitted below the threshold frequency.
2. The photoelectrons are admitted with a range of kinetic energy values, ranging from 0 to some maximum value. This max value increases with increasing frequency.
3. The intensity of the radiation has no affect on the Max KE value (intensity is the amount of energy hitting an area per second)
4. The higher the intensity of radiation, the more photoelectrons emitted per unit time
5. Emission of photoelectrons is instantaneous when the frequency is above the threshold frequency

Question 7

What are the two types of electron microscope

Answer 7

Transmission electron microscope and scanning tunnelling microscope

Question 8

What devices control the position of the probe in S.T.M.

Answer 8

Three piezoelectric transducers

Question 9

What piece of equipment was used my Michelson and Morley

Answer 9

An Interferometer

Question 10

What were the conclusions from the Michelson-Morley experiment

Answer 10

1. It’s impossible to measure absolute motion- thus the ‘ether’ doesn’t exist
2. The speed of light has the same value for all observers- this is invariant

Question 11

What are the two Postulates of Einstein’s theory of special relativity?

Answer 11

1. Physical laws have the same form in all inertial frames

2. The speed of light in free space is invariant