Jasmine Flashcards
Describe the role of the following in a Cathode ray tube (CRT):
a. electron gun
b. deflecting plates or coils
c. fluorescent screen
a. consists of the cathode and anode. A heating circuit heats the cathode, giving it enough energy to release electrons. They are fired towards the anode which focus the ray, and it continues through it.
b. deflecting plates or coils change the direction of the cathode ray, bending it so it can e used practically such as in cathode ray TVs
c. the fluorescent screen shows where the rays are produced, lighting up when it is hit by the ray allowing us to visualise it.
Recall two uses of CRTs
Cathode Ray TV and Oscilloscope (CRO), electron microscope
Briefly describe the operation of a cathode ray oscilloscope
Enables the visualisation of AC and DC current by using an electron gun to fire a cathode ray. The type of current supplied to the cathode is reflected through the pattern on the screen.
It uses a pair electric plates to deflect the cathode ray and control it vertically and horitzonally along the screen
Describe Hertz’s experiment on the production and detection of electromagnetic waves
Hertz used a transponder and a receiver to look for other kinds of electromagnetic waves. He used an oscillating spark and was able to induce a spark in the receiver over up to several hundred metres.
Recall four properties of the electromagnetic waves which Hertz discovered
- could be reflected from a metal mirror
- could be refracted
- could be polarised
- speed was similar to that of light
Explain the significance of Hertz measuring the speed of his electromagnetic waves
Hertz discovered it was the same as the speed of light, as Maxwell’s equations had predicted.
It was the first EMW other than visable light to be detected.
Describe how you could use a radio to simulate Hertz’s experiment
Using an induction coil with an oscillating spark, a radio can be tuned in to pick up the radio waves produced.
The oscillating spark produces radio waves which the radio can be tuned into to detect.
Predict which radio frequencies pick up Hertz’s waves better, AM or FM
AM
Recall two features of the photoelectric effect and explain how Einstein’s use of the photon allowed an explanation of them.
- greater intensity of light = more photons (of the same energy) ; therefore more electrons (of the same energy) leaving the surface of the metal.
- greater frequency = same amount of elctrons but with greater kinetic energy. -
Einstein used the concept of a photon to describe to help expalin these observations.
Identify the essential components of a photocell.
A photocell consists of
- metal grids to collect photoelectron,
- a layer of n-type and a layer of p-type silicon.
- wires connect the top of the photocell to the load to the base of the photocell, forming a circuit.
Describe how the photoelectric effect is applied in photocells
The photoelectric effect is used in photocells to take advantage of energy from the sun. Sunlight liberates electrons from the metal grid, causing to flow around the circuit giving power to the load.
Recall two uses of photocells
- Solar cells/photoconductive cells,
- phototubes
Compare the views of Planck and Einstein on how science relates to society
Einstein: - pacifist and Jew who opposed German militarism - believed science was something all of society should benefit from - Swiss citizenship in 1901 to escape Germany - warned US of German potential for atomic bomb, sparking the Manhattan project - remarked it was one of the most difficult decisions of his life.
Planck: - Nationalist - signed his name to the ‘Manifesto of the Ninety-Three’, supporting the German cause, whilst Einstein signed a counter-proposal. - Planck did not see the same moral implications that Einstein saw in developing science for war, and saw no moral imperative to oppose the Nazi regime. - He did, however, speak to see the Jewish scientists spared.
Define superconductivity
Refers to the ability to conduct electricity without resistance, meaning no energy loss.
Explain the significance of the ‘critical temperature’ in superconductivity
The temperature at which the resistance drops off. When a substance is cooled enough, it can conduct electricity without resistance.
Briefly describe the BCS theory of superconductivity
- John Bardeen, Leon Cooper and J. Robert Schrieffer - Superconductivity occurred because of an interaction between electrons - the lattice bends and electrons form ‘Cooper pairs’ in order to move through the lattice without resistance.
