Waves

What does T stand for and what does it mean?

Period, the time taken for one oscillation.

What is the wave speed equation?

v = fλ speed = frequency x wavelength

What are features of a longitudinal wave?

Oscillations of particles are parallel to the direction of energy transfer, has compressions and rarefactions

What are features of transverse waves?

Oscillations of particles are perpendicular to the direction of energy transfer.

What is a phase?

The position of a certain point on a wave cycle

What is phase difference?

How much a wave lags behind another wave

What is path difference?

The difference in distance travelled by 2 waves

What is superposition?

Where displacement of 2 waves is combined as they pass through each other.

What is a coherent light source?

One that has the same frequency, wavelength and a fixed phase difference.

When does constructive interference occur?

When 2 waves are in phase

When does destructive interference occur?

When 2 waves are out of phase

When are 2 waves in phase?

If they are at the same point in the wave cycle, meaning they have the same frequency and wavelength (not amplitude)

What are nodes?

Regions of no displacement

What are antinodes?

Regions of maximum displacement

Formula for wave speed on a string?

v = √T/u speed = √(tension of string/mass per unit length)

What is the equation for intensity?

I = P/A intensity = power/area

What is a refractive index?

A property which measures how much a material slows down light passing through it

What is the equation for refractive index?

n = c/v refractive index = speed of light in vacuum/speed of light in substance

What is Snell's law used for and what is it?

Calculations involving the refractions of light n1sinθ1 = n2sinθ2 n1 and n2 are refractive index 1 and 2 θ1 and θ2 are the angles of refraction in material 1 and 2

If n2 is more optically dense than n1, what happens to the light?

It slows down and bends towards the normal

What is the critical angle?

When the angle of refraction is 90°

How do you calculate the critical angle?

sinC = 1/n sin(critical angle) = refractive index 1 (usually air which is 1)/refractive index 2

When does total internal reflection occur?

When the angle of incidence is greater than the critical angle

What is focal length?

Distance from centre of lens to principal focus

What is power (lenses)?

The measure of a lens' ability to bend light (+ve in converging and -ve in diverging)

What is the equation for power of a lens?

P = 1/f Power = 1/focal length

What is the equation for power of several thin lenses?

P = P1 + P2 + P3 + ...

What is a real and virtual image?

A real image can be projected onto a screen, whereas virtual can't.

What is the equation for power of a lens (with v and u)?

1/v + 1/u = 1/f 1/right distance + 1/left distance = 1/focal length (power)

What is the equation for magnification of a lens?

m = v/u magnification = image height/object height

What is a polarised wave?

Wave that oscillates in only one plane (only transverse waves can be polarised)

What is diffraction?

The spreading out of waves as they pass through a gap

What is huygen's principle?

Each point of a wave front acts as a new wave source

What is a diffraction grating?

A slide containing many equally spaced slits close together

What is the diffraction grating equation?

dsinθ = nλ distance between slits x sin(angle to normal) = order x wavelength

What does an electron diffraction experiment produce?

A set of concentric rings, as they undergo diffraction in all directions, suggesting they move as waves

What is the de Broglie principle?

Suggests all particles have a wave and particle nature

What is de Broglie's equation?

λ=h/p wavelength of particle = Planck's constant/momentum of particle

What is the equation for photon energy and what is the significance of it?

E = hf photon energy = Planck's constant x frequency Since there is a constant, photon energy ∝ frequency

What is the photoelectric effect and threshold frequency?

Where photoelectrons are emitted from the surface of a metal after light of a certain frequency (threshold frequency) is shone on it

What is the photoelectric equation?

E = hf = Φ + Ek(max) Photon energy = hf = work function + max kinetic energy

How do you get a line spectrum?

By passing the light from a fluorescent tube through a diffraction grating

What do lines on a line spectrum represent?

Different wavelengths of light emitted

What is the emitted photon energy level equation?

ΔE = E1-E2 Photon energy = energy level 1 - energy level 2

Since E=hf, how can you rearrange with photon energy equation to find photon frequency?

f = (E1-E2)/h Photon frequency = (energy level 1 - energy level 2)/Planck's constant