Course

AS Physics: Matter and Waves (9702)

Name: AS Physics: Matter and Waves (9702)
Price: 1999 BDT

9702 topics 6, 7 and 8. Stress, strain and the Young modulus, then waves: every interference pattern in the syllabus is superposition applied twice.

41 lessons4h 7mEnglish

What you'll learn

Read a stress-strain graph, and say what the gradient and the area under it each mean
Tell a material property from a sample property, which is the point of stress and strain
Use the wave equation, and describe a wave by phase rather than only by shape
Apply the principle of superposition to explain a stationary wave and an interference pattern
Use the double-slit and grating formulae, and say which one a given setup needs

Requirements

AS topic 5: work as the area under a force-extension graph, and the conservation of energy
AS topic 1: units and prefixes, since the Young modulus is quoted in GPa
Able to read a gradient and an area off a graph, and to say what each represents
Basic trigonometry, and comfort with angles in degrees and radians

Course content

41 lessons · 4h 7m

6.1-6.2 · Deformation of solids

What stretches, how far, and whether it comes back. The spring constant describes one wire; stress and strain describe the material, and their ratio is the Young modulus. Ends with the energy stored in a stretched wire and the experiment the exam asks you to describe.

0/12

Load and extension rise together

Double the load on a steel wire and predict what happens to the extension.

Preview5m 2.

k describes one wire, not the metal

Double the diameter and the gradient does not double. Find out what it does instead.

Preview6m

Where the straight line ends

Hooke law holds up to a point. Find the point, and separate two words the exam confuses.

Does it come back?

Take the load off and read the extension at zero. Sometimes it is not zero.

Stress is load shared over area

Two wires carry the same 60 N and only one is near snapping. Area is the reason.

Strain compares stretch with length

A 2 mm stretch means nothing until you know what it started as.

The graph that does not move

Change the wire as much as you like. One of the two graphs swings, and the other stays exactly where it is.

Preview7m

Two ways to fail

Glass gives no warning. Copper draws out first. The graph shows which is which.

Energy stored is the area, not F times x

The load grows from zero as you stretch, so the work done is a triangle.

10.

Measuring E, and the one reading to take care over

Four measurements give E. An error in one of them counts twice.

11.

One exam question, end to end

Eight marks, three parts, no options: stress, extension and stored energy for one loaded steel wire.

12.

Deformation: quick revision

Reconnect force, material properties and stored energy, then rehearse a safe Young modulus route.

7.1-7.5 · Waves

What a progressive wave carries and what it leaves behind. The two graphs and how to tell them apart, v = fλ, phase difference, transverse against longitudinal, intensity, polarisation, the Doppler shift of a moving source, and the electromagnetic spectrum.

0/13

A wave moves energy, not matter

A leaf on rippling water bobs and stays. Decide what actually travels before you look.

Preview6m 2.

One particle, one cycle

Ignore the whole wave and watch a single particle. Period and frequency come from that trace.

Preview6m

The snapshot graph and the history graph

Two graphs with the same shape and different horizontal axes. Only one of them shows wavelength.

Why v = fλ has to be true

Hold the speed fixed, double the frequency, and predict the wavelength before you move the slider.

Wavefronts and phase difference

Every point on one wavefront is in phase. Put a number on how far out of phase two points are.

Which way the particles oscillate

Across the direction of travel or along it. Sound and light answer that question differently.

Intensity depends on amplitude squared

Double the amplitude and the intensity does not double. Commit to a factor first.

Only a transverse wave can be polarised

A filter passes one component of the amplitude, and squaring that component gives Malus law.

Why the horn changes pitch as the bus passes

A highway bus horn is higher coming and lower going. Decide what the driver hears.

10.

Putting a number on the Doppler shift

Where the moving-source formula comes from, and which sign belongs to which direction.

11.

One family, all at the speed of light

Radio to gamma is one continuous range. Raise a tube voltage and watch the short edge move.

12.

One exam question, end to end

Six marks, three parts, no options: frequency, a phase difference, then what doubling the amplitude does.

13.

Rebuild AS waves in 7 minutes

Connect the wave relationships, repair a phase error, then review only weak ideas.

8.1-8.4 · Superposition

What happens where two waves meet. Displacements add, a reflected wave locks into nodes and antinodes, a gap spreads a wavefront, and coherent sources build fringes you can measure: λ = ax/D for two slits and d sin θ = nλ for a grating.

0/13

Displacements add, then the waves continue

A crest meets an equal trough. Decide what the string looks like at the instant of overlap.

Preview6m 2.

A wave meets its own reflection

Compare travelling and stationary waves, then use fixed nodes and moving antinodes to read wavelength.

Preview7m

Nodes sit half a wavelength apart

Some points never move. Measure between two of them and you have measured a wavelength.

Only certain frequencies fit

Both ends are nodes, so only whole half wavelengths fit. That gives λ = 2L/n.

The comparison the examiner asks for

Energy, amplitude and phase are the three lines that separate the two kinds of wave.

A wave spreads when it passes a gap

Sound turns a corner and light does not. The gap width compared with λ decides it.

Why two torches never make fringes

A steady pattern needs the same frequency and a constant phase difference between the sources.

Path difference decides bright or dark

Two waves arrive after unequal journeys. The difference in wavelengths settles what you see.

Young fringes and λ = ax / D

Move the slits closer and predict the fringe spacing before the readout tells you.

10.

Using the fringes to measure a wavelength

The same equation run backwards, and the measurement that carries most of the uncertainty.

11.

Many slits: d sin θ = nλ

The colours on a CD under a tube light, and why large angles need sin θ instead of x/D.

12.

One exam question, end to end

Eight marks, three parts, no options: a grating spacing, a first order angle, then a fringe spacing.

13.

Superposition: quick revision

Reconnect interference, stationary waves and diffraction, then repair the path-difference trap.

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