Physics - Unit 4 AOS 1

Mechanical waves, light's wave-particle duality, Young's double split, photoelectric effect, special relativity, mass-energy equivalence

Wave

The transmission of energy via oscillations from one location to another without the net transfer of matter

Transverse wave

A wave with oscillations perpendicular to the direction of wave travel and energy transmission

Longitudinal wave

A wave with oscillations parallel to the direction of wave travel and energy transmission.

Superposition

The addition of overlapping waves in the same medium

Constructive interference

Superposition creating a larger resultant waveD

Destructive interference

Superposition resulting in a smaller or zero amplitude wave.

Coherent

Wave sources that create waves of the same frequency and constant phase difference in the same medium

Path difference

The difference in distance travelled by two waves from their sources to the same point

Antinode

A point where constructive interference consistently occurs

Node

A point in a standing wave where destructive interference consistently occurs.

Standing waves

Two waves of the same frequency and amplitude travelling in opposite directions superimpose to create stationary regions of max and min displacement.

Travelling wave

A wave that propogates through a medium, carrying energy from one location to another

Fundametal frequency

The lowest frequency of a standing wave that will form in a given medium.

Diffraction

The spread of a wave around an abostacle or through an aperture.

Aperture

The hole, gap, or s lit through which a wave travels

Limited diffraction

Occurs when λ/w ≤ 1

Significant diffraction

Occurs when λ/w ≥ 1

Electromagnetic wave

A transverse wave composed of a changing electric field perpendicular to a changing magetic field.

Speed of light in a vacuum

3.0 × 10⁸ ms^-1

Electron-volt (eV)

Equal to 1.6 × 10^-19 J

Photoelectrons

Electrons emitted in the photoelectric effect

Work function

The minimum energy of light required to release the most loosely bound electron from a particular metal surface

Stopping voltage

The voltage required to stop electrons with the highest kinetic energy and hence reduce photocurrent to zero.

Retarding voltage

The voltage required to slow electrons with the highest kinetic energy.

Changing intensity

Does not change stopping voltage, changes max photocurrent

Changing frequency

Does not change photocurrent, changes max kinetic energy and stopping voltage

De Broglie wavelength

De Broglie wavelength is associated with objects made of matter. De Broglie wavelength and wavelength of photon will be the same if they have the same momentum, p

Absorption spectrum

Specific set of frequencies or wavelengths of light that an element or compound absorbs due to electron energy transitions

Emission spectrium

Specific set of frequencies or wavelengths of light that an element or compound emits due to electron energy transitions

Einstein’s first postulate

The laws of physics are the same in all intertial (non-accelerated) frames of reference (agrees with classical relativity)

Einstein’s second postulate

The speed of light has a constant value for all observers regardless of their motion or the motion of the source (contradicts classical relativity)

Ether

The hypothetical massless medium for electromagnetic waves

Michelson-Morley Experiment

Aether does not exist, therefore light does not need a medium. Supports Einsteins’ theory of special relativity

Proper time

Time interval between two events measured in a reference fram where two events occur at the same point in space (Holding the clock)

Dilated time

Time Time interval between two events measured in a reference fram where two events occur at different points in space

Proper length

Length of an object measured in a fram of reference where the object is at rest

Contracted length

Length of an object measured in a reference fram where the object is moving

Muon example

In the frame of reference of the Muon, it will experience proper time but will experience contracted length that allows for it to travel further during its half-life and make it to the surface of Earth before decaying

Lorentz factor

A dimensionless number that quantifies the size of relativistic effects such as time dilation and length contraction

Mass-energy equivalence

Mass can be considered a form of energy; mass can be converted into energy and energy can be converted into mass

Total mass-energy

Sum of kinetic and rest energies of a mass or system