Physics Flashcards
Recall mean(s) to improve the efficiency of a transformer
The efficiency of a transformer can be improved through:
- Placing a soft iron core between the primary and secondary coil
- Soak in oils as oils have a high heat capacity and is an electrical insulator
- Laminate the core with layers of insulating material to reduce eddy currents
- Increase the cross-sectional area of wires; reduces ohmic resistance
Consider a non-ideal transformer. Identify what is conserved within the system and what is not.
Power and energy is lost through heat etc.
Voltage is conserved
Current is not conserved
Using Faraday’s Law, how does an AC Induction Motor function
Recall in a traditional motor, the armature rotates through the stationary magnetic field to induce an emf.
In an AC Induction Motor, the magnetic field rotates in a 3-phase nature around a stationary squirrel cage.
Slip speed –> the squirrel cage rotates to ‘chase’ the magnetic field
Recall James Clerk Maxwell’s contribution(s) to the properties of light
Maxwell:
- United the fields of electricity and magnetism
- Applied pre-existing scientific laws: a changing magnetic field induces an electric field and a changing electric field induces a magnetic field
- Proposed electromagnetic waves:
Self-propagating
Perpendicular oscillating magnetic field and electric field
Speed of 1/root(µ0ε0) –> predicted light was an electromagnetic wave as it was approximate to experimental observations - Predicted the existence of an electromagnetic spectrum
Recall Hertz’s experiment and relate to the photoelectric effect
Hertz’s experiment confirmed the existence of electromagnetic waves.
Hertz supplied AC voltage to a capacitor to induce a spark across a spark gap to a receiving loop. Although there was no electrical connection, a weaker spark was observed –> indicating energy was lost as electromagnetic radiation.
Using the frequency and forming standing waves, the speed of the radio waves could be calculated
When UV light was shone, the spark length increased
When glass [a dielectric material] was placed, the spark length decreased
The first recorded observation of the photoelectric effect
Recall the historical measurement(s) of the speed of light
Historical measurements of the speed of light:
- Roemer’s Measurement of Io’s orbit
- Fizeau’s Cogwheel
- Foucault’s Mirrors
Describe how Roemer measured the speed of light
Roemer observed the orbital period of Io was inconsistent due to the speed of light being finite and Earth’s relative velocity to Io’s orbit.
Receding velocity –> larger apparent period
Approaching velocity –> smaller apparent period
Time discrepancy = 22 minutes to cross the length of Earth’s orbit
Describe how Fizeau measured the speed of light
Fizeau passed a beam of light through a toothed cogwheel with slits and reflected back via a mirror. Based on the angular velocity of the cogwheel and the velocity of the speed of light, the speed may or may not pass back through a slit or get blocked.
Recall the contemporary measurement(s) of the speed of light
Essen Cavity Resonator
Last-Ditch: Rosa & Dorsey [Used Maxwell’s findings to calculate the speed of light, accuracy was inhibited by the definition of the standard unit of Ohms]
Describe how Essen measured the speed of light
Essen used a Microwave Cavity Resonator with microwaves of a known frequency. The resonator was of a variable length –> Essen found the exact lengths for which resonance occurred, which allowed him to find the wavelengths.
Explain how Planck accounted for the shape of the blackbody curve
Planck proposed that the absorption and emission of radiation are inherently quantised as discrete amounts, known as quanta.
At higher frequencies, a greater gap exists between energy levels and thus, there is a lesser likelihood that atomic oscillators exist in an excited state. Ultimately, a lower intensity at low wavelengths.
Recall the experimental evidence for Special Relativity
Rossi-Hall –> Mu-mesons
Experiment conducted on Mount Washington
A greater quantity of mu-mesons was detected on the surface of the Earth than predicted by its half-life.
Length contraction [mu-meson] + Time dilation [stationary observer]
Hafele-Keating experiment
Atomic clocks flown to the East and West; Earth rotation eastly
