Below are some revision notes about the G492 paper for Physics A level. You may want to also look at Section C Revision Notes too. Feel free to skip to the parts most relevant to you.

### Displacement – Time Graphs

- The displacement is a distance is a
*specific*direction. - With these graphs, the gradient is the velocity.

### Velocity – Time Graphs

- A velocity is a speed is a
*specific*direction. - The gradient of these graphs is acceleration.
- The area under the line is the displacement.

### Superposition (and interference)

**Huygen’s construction**suggested that a wave front can be considered as a line of secondary sources of waves. Even though there wavelets (secondary waves) are not real, they give a way of constructing where the wave front will go and maybe even more.

### Reflection

*i*, equals the angle of reflection,

*r*. The rule of reflection is true at each reflected point. The trip time for every path to reach the focus,

*F*, should be in phase and the same.

### Light as a Wave or a Particle?

We can measure light as a wave. To do this, we use the Young’s Two Slit Experiment which proves light to be a wave. The light is shined in two slits producing a pattern of light fringes and dark fringes on a nearby screen. The central fringe has a wave difference of 0, the first dark fringe has a path difference of λ/2. The next bright fringe has a path difference of λ and so on.

We can measure the Two Slit Experiment through four variables:

- λ = wavelength of light.
*d*= separation of the two slits.*s*= separation of the fringes (bright fringe-bright fringe or dark fringe-dark fringe).*L*= distance between slits and screen.

**λ**

*L = d s*although it is just an approximation.

**Ultra-Violet – Highest Energy****Violet****Indigo****Blue****Green****Yellow****Orange****Red****Infra-Red – Lowest Energy**

The lower the the energy the light has, the lower the frequency it has. This means it will have a longer wavelength.

When using a diffraction grating, we can use the equation nλ = d sinX (where n is the number of fringes it is from the centre):

**Single Slit Experiment**

**Wavelength = wavelength****d = the width of the single slit****Feta (X) = angle to the the first dark fringe**

**Double Slit Experiment**

**Wavelength = wavelength****d = separation of the double slits****Feta (X) = angle to the first bright fringe.**

## λ = d sin X

- As λ increases, the angle will increase.
- As d increases, the angle will decrease.

### Photoelectric Effect

hF = eV + hf0

Where hF is the total amount of energy put into the electron, eV is the energy of the electron and hf0 is the energy required to move the electron (and escape the metal).

**Increasing the intensity of the frequency**will move more electrons from the surface of the metal.

**Increasing the frequency of the light**but keeping the intensity the same will increase the light energy to the electron making the electrons escape from the surface of the metal quicker. The number of electrons escaping the surface will be the same. The stopping potential is the voltage needed to make the electrons stationary.

### Electron Diffraction

Wavelength = Planck’s constant / mass of electron X velocity of electron (λ=h/p)

For which the mass of an electron is 9.1×10^-131kg. The electrons show particle and wave properties from the electron diffraction experiment. Electrons are fired in a vacuum from an electron gun (showing particle properties). They then go through a thin graphite screen causing them to diffract showing properties of waves.

For example, the diffraction grating of electrons at 3000V = 24 mm.**Energy of electrons at 3000V **= 3000eV = 1.6×10^-19 x 3000 = 4.8×10^-16**What is the frequency of the electrons? **E = hf. F = 7.2×1-^17.**What is their wavelength? **v = fλ. λ = 4.4×10-11m.

Another equation could be used to work out the wave length of electrons:

## λ= sxd / L

Where λ is the wavelength, d is the spacing between light fringes, s is the spacing between the graphite and L is the length between the graphite and tube screen.

Some more equations:

**p = h/****λ –**This can be used for high voltages.**p = square root of 2meV**– This cannot be used for high voltages.**h/****λ = square root of 2meV**– This clear that 1/λ is proportional to the square root of V.

λ = d sinX

If λ decreases, sinX will decrease.

If angle X decreases, the rings get smaller.

So, if we increase V, the rings should get smaller.

### Quantum Physics

- The trip time is the time any particle takes to on from one place to another.
- The path is the path the particle takes to on a trip from one place to another.
- The shorter the trip time, the smaller the phaser.
- The probability of a path is the resultant phaser value squared.
- If amplitude has decreases, it will not be as bright.