Physics unit 2- waves and astronomy

How do waves transfer energy but no matter?

Waves transfer energy through the oscillation of particles in a medium since as the wave travels, it causes the particles to move temporarily, which creates oscillations, but the overall matter does not travel with the wave; instead, it just vibrates around an equilibrium position.

Photons

discrete packets of EM radiation with energy proportional to their frequency or inversely proportional to their wavelength

• AKA particle of light

electromagnetic waves

consist of vibrating electric and magneti cfeilds and travel through empty space or matter at the constant speed of light and transfer energy through electromagnetic radiation.

Name the structures

1. Peak

2. Amplitude

3. Wavelength

4. Trough

5. Rest Position

λ

wavelength= distance between two peaks or troughs

f

frequency, the numebr of waves per unit time eg. per second is Hertz(Hz)

State that light travelis in …..

a straight line

wave vs. wave front

A wavefront is effectively a line connecting the same point on each wave and the distance between two wavefronts is the wavelength. A ray also represents a wave but it is a line perpendicular to the wave fronts.

How do the waves travel

When they travel through matter some energy is lost as they pass through but when they travel through space no energy is lost so the waves don’t get weaker as they travel but the energy is “diluted” as the wave goes further away from it’s source since the energy spreads out over a larger area.

How do the waves begin_

A charged particle vibrates which causes the electric feild around it to vibrate too, causing the magnetic feild to vibrate. The two vibrating fields then combine to make up an electromagnetic wave where the electric and magnetic feilds are perpendicular to each other.

Universal wave equation

V=fλ bc velocity is distance over time and 1/T is frequency.

V is the wave speed in ms^-1and only changed when medium is chnaged

f is the frequency in Hz

λ is the wavelength in metres

reflection

when light rays strike a reflective surface the angle of incidence is equal to the angle of reflection(both measured from the normal). If the reflecting surface is very smooth specular reflection occurs when rays are all reflected in the same direction making the object visible and identifiable in the reflection whilst if it occurs on a rough surface, diffuse reflection occurs.

refraction

Refraction is the bending of light as it passes from one medium to another at an angle, and it happens because light travels at different speeds in different materials. Light travels slower in more optically dense mediums so when light travels from a less dense to more dense, the ray bends towards the normal and when it travels from a dense to a less dense light bends away from the normal. THE FREQUENCY STAYS THE SAME SINCE IT’S ONLY AFFECTED BY THE SOURCE.

difraction

When waves spread out/bend and change direction as they pass through a gap or around an obstacle(edge), they are affected by the wavelengths of the waves and how wide the gap is. When there is a significant difference between the gap width and the wavelength, very little diffraction occurs so when they are equal the most diffraction occurs.

total internal reflection

Occurs when the incident angle excees the critical angle(incident angle at which angle of refraction is 90 degrees), and only occurs when light travels from a denser medium to a less dense medium.

optical fibres-how TI reflection is used

• optical fibres transport info over long distances through the use of light pulses

• made of thing glass or plastic(smooth so there is specular reflection) as light is reflected inside the tube everytime it hits the surface so it bounces back and fourth throughout the entire tube.

• Has a spectograph at the end where the reciever is which is a prism that splits the ray of light by wavelength/frequencey to show all colours of light.

refractive index

a measure of the speed of light as it passes through that material, compared to the speed of light as it passes through a vacuum, materials through which light travels more slowly have a higher refractive index.

what happens when 2 black holes merge

they spiral around eahc other until they evenutally collide and send out gravitational waves.

Gravitational Waves

What is the Doppler Effect

meteor/meteriorite/meteroid

universe

galaxy

A moon

Stars

Asteroids

comets

• Comets are icy objects that have very elliptical orbits around the Sun.

• Comet tails form as ice vaporizes and glows in the Sun's light.

• Short-period comets come from the Kuiper belt beyond Neptune, and long-period comets come from the Oort cloud far out away from the Sun.

electromagnetic spectrum

Red

Radio waves- metres 10²

Microwaves- centimetres 10^-2

Infrared- millimetres/micrometres 10^-4

Visible- 400-800 nanometres 10^-7

Ultraviolet- nanometres 10^-8

X-Ray- 10^-10

Gamma Ray- 10^{-12 or -14}

Violet

Radio waves

Longest wavelength and lowest frequency and lowest energy, used for radio, television braodcasts and cell phone transmissions and radar.

• eg. for AM(Amplitude modification) broadcasts where sound signals are encoded by changing the amplitude of radio waves and uses longer wavelngths so they can reach recivers far away.

Microwaves

Used for heating up food in microwave ovens becuase it heats up the water in the food, cell phone transmissions, and wifi and remotes.

Infrared

it’s emited by warm objects and can be used to detect living things. eg. for night vision goggles

Visible light

we see light of different wavelengths as different colors of light, from red light, which has the longest wavelength, to violet light, which has the shortest wavelength and when combined makes white light.

Ultraviolet

Is very useful for killing bacteria in food and to sterilise lab equiptment and our skin needs it to make vitamin D.

X-Ray

Has enough energy to pass through soft tissues like skin but not enough to pass through bones and teetch so used for scans medically and in the airport.

Gamma Ray

Has the shortest wavelength but highest frequency and most energy, used to destruy cancerous cells during treatment.

describe the two types of telescopes and how these are able to create images of stars