physics unit 4 terms + theory

Wave

A transfer of energy in the form of a travelling disturbance, caused by a vibrating source. Can also be referred to as a series of pulses

Pulse

A single travelling disturbance caused by a vibrating source. Repeated of these compose a wave

Vibration

Repeated oscillation about some equilibrium point. Vibrating objects undergoing SHM can create waves.

Frequency

The number of complete cycles of a wave which pass a point in a given time. Measured in Hz. 1 hz = 1 cycle per second

Period

The amount of time for one complete wave (cycle) to pass. Measured in seconds

Describe the relationship between the frequency and period of a wave

Frequency and Period are reciprocals of each other, as one measures the time for a cycle to complete and the other measures the number of cycles pass in that time. When given one, the other can be found by putting the given to the power if negative 1.

Amplitude

The displacement of the particle from the rest position, measured in meters.

In -Phase

when two particles are at the same amplitude, moving in the same direction on a wave.

Wavelength

The distance from one point on a wave (in-phase) to another point (also in-phase). Measures in meters, but often given in nanometers

Conversion nm to m

To get meters from nanometers, multiply the nanometers by 10^-9

Cycle

One complete wave

Crest

The top of the wave

Trough

The bottom of the wave

Mechanical waves

Waves that need a medium to transfer energy and travel. The energy is transferred through particle motion and is not dependent on the wave’s frequency. Energy is proportional to the square of the amplitude (E=KA²)

Energy Waves

Waves that can travel and transfer energy without a medium. Energy is dependant on frequency, and the distance travelled is dependent on encountered damping. There are 2 types: Longitudinal and transverse

Longitudinal waves

Waves in which the particles/energy vibrate parrallel to the direction of the waves motion. This includes sound and slinky waves

Transverse waves

Waves in which the particles/energy vibrate perpendicular to the direction of the waves motion. This includes light and waves on a string

The wave equation

Used to find the speed of a wave. Speed(m/s)= wavelength(m)xfrequency(Hz)

The electromagnetic spectrum

A spectrum that classifies types of light. In order from lowest energy+frequency to highest energy+frequency: radio, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays

Light propagation

The travelling of light. Light can travel in no medium as it is made up of vibrating electric fields, which cause magnetic fields to vibrates at right angles to each other. This describes how light is an electromagnetic wave that can travel in a vacuum (no medium)

Rectilinear propagation

Describes how light travels in a straight line. Shadows are evidence of this

A ray of light

A path taken by light energy, represented with a singular arrow for a singular ray

A beam of light

A stream of light rays, represented using multiple arrows. Can be converging (ends at the same point), diverging (begins from the same point and spreads out), or parallel

The superposition principle

Two or more waves can move through eachother, and when they do, a net wave forms at the point of interference which has an amplitude that is the sum of the interfering waves amplitudes.

Interference

The result of two or more waves meeting at a particular point in space at the same time. 2 types; constructive and destructive

Constructive interference

Occurs when the overlap of pulses create a pulse of greater amplitude whilst they interfere. A result from waves moving in the same direction in phase

Destructive interference

Occurs when the overlap of pulses create a pulse of lesser amplitude. A result of two waves moving in opposition directions out of phase interfering

Total destructive interference

Occurs when two waves of the same amplitude interfere, but since they are out of phase moving in opposite directions, they totally cancel each other out.

What happens after 2 waves interfere?

Both waves continue travelling, returning to their original amplitude, moving in the direction as before. Even after total interference, waves return to normal.

Absorbed waves

When waves meet a different kind of matter (ie: wall), the energy can be dissipated or turned into other kinds of energy. Examples include sound waves in sound proof rooms and water waves and breakwaters

Transmitted waves

When waves meet a different kind of matter, the wave can travel through the substance. Examples include light waves through glass, microwaves through paper and x-rays through skin

Reflected waves

When waves meet a different kind of matter, they can rebound off the surface. Examples include light waves off a mirror and sound waves off a canyon wall. If a pulse meets a fixed end, it reflects back inverted, but if it hits a loose end it reflects on the same side.

Properties of light

Transmission, diffraction, reflection and refraction

Transmission

When light passes through a material, it may lose some energy and slow down, as well as heating up the medium

Diffraction

As a wave passes through a narrow slit (or an edge) around the same size as the wavelength, it will bend to fill the space behind it. Water waves are known to do this.

Reflection

Light will bounce off certain objects. Specular reflection occurs when the object is smooth, and you can see your reflection. Diffuse reflection occurs if an object is rough, and an image cant be seen.

Law of reflection

States that the angle of incidence must equal the angle of reflection, and the incident and reflected rays lie in the same plane.m

Images in plane mirrors

Images are upright, virtual and undergo lateral inversion (left and right are switched)

Refraction

The bending of light as it passes from one optical medium to another.

What happens when light moves into a less dense medium

The light speeds up and bends away from the normal line (angle of incidence<angle of refraction)

What happens when light moves into a more dense medium

The light slows and bends towards the normal line. ( angle of incidence>angle of refraction)

Index of refraction (n)

A measure of the speed of light in a medium when compared to air. Has no unit. Equal to the speed of light divided by the speed of light in the medium

Index of light in air

1.00, as air does not slow light down

Snells law

States that the ratio of the sines of the angles of incidence and refraction is equal to the ratio of the phase velocities of the 2 medium

Total internal reflection

Occurs when light is travelling from an optically dense medium to a less optically dense medium, as the angle of refraction is greater than incidence. At some particular angle of incidence, called the critical angle, the reflected rays move parallel to the boundary so the angle equals 90’. Once we surpass the critical angle, the light reflects inwards on itself as total internal reflection occurs.

How do diamonds sparkle?

This is due to the cut of the jewel and total internal reflection. As rays enter the top of the diamond, they will surpass the critical angle due to the diamonds shape and total internally reflect until they reach the top face of it and exit, creating the sparkle that we see.

Explain how mirages are seen

Warm air is less dense than cool air, so light travelling near a hot surface will totally internally reflect as it enters. This creates an inverted palm tree, and sand may look like water

maxima

Bright lines that appear when light waves constructively interfere with each other

Minima

Dark lines that appear when light waves destructively interfere with each other

Double slit interference

A way to cause light waves to interfere as they diffract through narrow slits. The slit size must be close to the wavelength of light. Result is many maxima, which is proof of light acting as a wave as the light will diffract around the slits rather than travel through in a parallel way (which would be expected if light acted only as a particle).

Doppler effect

The apparent shift in light from a moving source, resulting in a red or blue shift of the lights frequency.

Red shift

A result of the doppler effect the occurs when the source is moving away from the light. The waves spread out and frequency decreases, so light may appear towards the left side of the electromagnetic spectrum

Blue shift

A result pf the doppler effect that occurs when the source is moving towards the light. The waves appear closer, causing the frequency to increase, which causes light to appear towards the right of the electromagnetic spectrum.

How does sound travel

A vibrating source causes pressure fluctuations, causing neighbouring air pressure to change. These fluctuations allow sound to travel in areas of high pressure called compressions and low pressure called rarefactions through the air. It travels as a longitudinal wave through a medium (air particles)

What factors affect the speed of sound?

-medium; the stiffer and more compact particles=faster

-Density; denser medium=faster

-temperature; particles move faster due to heat= energy transmitted faster

What is the speed of sound regardless of temperature

332 m/s

Standing wave

Interférence that occurs when 2 waves of the same frequency, travelling in the same direction meet in the same medium. Typically occurs when a wave meets its reflection.

Nodes

Areas of total destructive interference on a standing wave. Appear to not move.

Antinodes

Areas of constructive interference in a standing wave. Represented using n. The number of harmonics on a closed or open standing wave is equal to the the number of this

Fundamental frequency

The lowest frequency at which a standing wave will occur, also known as the first resonance or harmonic

Inter nodal distance

Distance between nodes, equal to half of the wavelength

Resonance

The vibrating response of an object to a force from a source that has the same natural frequency of the object

Resonant lengths

For some musical instruments, the length of the air column of which the wave inhabits can affect the frequency and sound produced.

Doppler effect of sound

Occurs when the source of a sound is moving, causing an apparent shift of frequency. Equal to the change of frequency, meaning the frequency heard - the frequency of the source