physics revision for resit

Diffraction

Spreading of a wave as it passes through a gap or around an edge

What is the diffraction grating formula?

nλ = d sin(θ)

• d = slit spacing / distance between lines in metres (d = 1/N) • θ = angle between the central normal (zero-order) and the maximum

• n = order number (0, 1, 2, ...)

• λ = wavelength in metres

Nanometre (nm) to Metre (m)

1 nm = 1 × 10⁻⁹ m (multiply by 10⁻⁹)

Micrometre (μm) to Metre (m)

1 μm = 1 × 10⁻⁶ m (multiply by 10⁻⁶)

Millimetre (mm) to Metre (m)

1 mm = 1 × 10⁻³ m (multiply by 10⁻³)

Picometre (pm) to Metre (m)

1 pm = 1 × 10⁻¹² m (multiply by 10⁻¹²)

What is the definition of coherent waves?

Waves that have a constant phase difference (and the same frequency).

What is the double-slit interference formula for fringe separation?

x = (D λ ) / a

• λ = wavelength of light (m)

• a = slit separation / distance between the two slits (m)

• x = fringe separation / distance between adjacent bright (or dark) fringes (m)

• D = distance between the slits and the screen (m)

What is the principle of superposition?

When two waves meet , The resultant displacement is the sum of the individual displacements.

What is constructive interference?

When two coherent waves arrive in phase (0°, 360° or whole λ path difference), their displacements add together to create a maximum amplitude.

What is destructive interference?

When two coherent waves arrive in antiphase (180° or half λ path difference), their displacements subtract to create a minimum amplitude (zero if equal amplitudes).

What is path difference?

The difference in distance traveled by two waves from their coherent sources to a given point (measured in metres or fractions of λ).

What are the path difference and phase difference conditions for a maximum (constructive interference)?

Path difference = nλ (0, 1λ, 2λ...); Phase difference = 0°, 360°, 720° (in phase).

What is polarisation?

The restriction of wave oscillations to a single plane perpendicular to the direction of energy propagation (applies only to transverse waves).

State Malus's Law and define its variables.

I = I0 cos²(θ),

where I0 is incident intensity,

I is transmitted intensity,

θ is the angle between the plane of polarisation and the filter's transmission axis.

What are the path difference and phase difference conditions for a minimum (destructive interference)?

Path difference = (n + 0.5)λ (0.5λ, 1.5λ, 2.5λ...); Phase difference = 180°, 540° (antiphase).

How does wave intensity (I) relate mathematically to amplitude (A)?

Intensity is proportional to Amplitude²:

(I / I0) = (A / A0)².

Why can sound waves not be polarised?

Sound waves are longitudinal (oscillations are parallel to energy propagation); only transverse waves can be polarised.