Course

A2 Physics: Medical Physics, Astronomy and Cosmology (9702)

Name: A2 Physics: Medical Physics, Astronomy and Cosmology (9702)
Price: 1799 BDT

9702 topics 24 and 25. Medical diagnostic technologies (ultrasound reflection, X-ray attenuation, CT reconstruction, PET annihilation) and astronomical cosmology (standard candles, Stefan-Boltzmann, Wien, Hubble expansion and the Big Bang).

32 lessons3h 18mEnglish

What you'll learn

Calculate acoustic impedance Z = rho c and reflection coefficient alpha at tissue boundaries
Apply the X-ray exponential attenuation law I = I0 exp(-mu x) and half-value thickness
Explain 2D voxel matrix attenuation reconstruction in Computed Tomography (CT)
Describe electron-positron annihilation and 511 keV collinear photon coincidence detection in PET
Use radiant flux intensity F = L / (4 pi d^2) and standard candles to determine astronomical distances
Apply Stefan-Boltzmann law and Wien displacement law to calculate stellar surface temperature and radius
Determine galaxy recession velocities from spectral redshift and estimate universe age via Hubble constant

Requirements

AS Level waves, optics, and photon fundamentals (E = hf)
Comfortable with natural logarithms, exponentials, and inverse-square algebra
Familiar with Doppler effect and electromagnetic radiation spectrum

Course content

32 lessons · 3h 18m

24.1-24.3 · Medical physics

How an X-ray tube makes its spectrum, how CT restores depth, how ultrasound creates and times echoes, and how PET locates a tracer from paired photons.

0/17

A radiograph is a transmission image

A chest X-ray at a diagnostic centre records what got through, not what came back.

Preview6m 2.

Inside the X-ray tube

Guess what fraction of the electron energy leaves as X-rays before you check.

Preview7m

The sharp cut-off: hf = eV

The spectrum stops dead at one energy, and the tube voltage sets where.

The characteristic lines

Change the target metal and the spikes move, while the continuous background stays.

Attenuation: I = I₀ exp(−μx)

Each extra centimetre removes the same fraction, never the same number of photons.

The linear attenuation coefficient

Two curves, bone and tissue, and the gap between them is the whole reason X-rays work.

Half-value thickness

Work out the lead needed to cut a beam to one eighth, using halvings alone.

Contrast, and the price of getting it

Low photon energy gives the best contrast and the worst dose. Find the compromise.

Computed tomography in outline

One view flattens depth into a single number. Many views put the depth back.

10.

The piezoelectric transducer

One crystal sends the pulse and receives the echo, because the effect works both ways.

11.

Acoustic impedance and the echo

A pulse reflects where the medium changes. Z = ρc says how much of it comes back.

12.

Echo time becomes image depth

The timer measures a round trip. Halving ct places the reflecting boundary at the correct depth.

13.

Frequency: detail versus penetration

Higher frequency separates closer boundaries, but stronger attenuation makes deep echoes harder to detect.

14.

PET: the tracer and the annihilation

The source goes inside the patient this time, and one photon could not carry the energy away.

15.

Coincidence and the line of response

One line says almost nothing. Collect a thousand and the tracer appears where they cross.

16.

One exam question, end to end

Ten marks, four parts, no options: transmitted fraction, half-value thickness, impedance, then why gel is used.

17.

Medical physics: quick revision

Reconnect X-ray, CT, ultrasound and PET signal paths, then repair the acoustic-boundary trap.

25.1-25.3 · Astronomy and cosmology

How a distance is measured from a brightness, how a colour becomes a temperature, and how a shifted spectral line becomes a speed. Standard candles, the inverse square law, Stefan and Wien, redshift, Hubble law, and the Big Bang that follows from it.

0/13

Luminosity is not brightness

Two stars, one looks brighter. Decide whether it has to be the more powerful one.

Preview6m 2.

Where the 4πd² comes from

All the power crosses every sphere you draw. The sphere is what grows, not the power.

Preview6m

A known luminosity becomes a distance

Measure the flux, look up the luminosity, and the distance falls out of one equation.

Stefan law: how big and how hot

Double the surface temperature. Commit to a luminosity factor before you move the slider.

Determining the radius of a star

Show that Stefan law gives the Sun a radius of about 7 × 10⁸ m.

Wien law: the peak moves

A hotter star peaks at a shorter wavelength. Predict the direction before you slide.

Colour is a thermometer

Red Betelgeuse and blue-white Rigel sit in the same constellation. One is far hotter.

Light from a galaxy that is moving away

Decide whether the galaxy emits redder light, or whether the wavelength changes on the way.

Putting a number on the redshift

A hydrogen line arrives 14 nm late. Determine how fast the galaxy is receding.

10.

Hubble law and what its gradient means

Every galaxy recedes, and the far ones fastest. Decide whether that puts us at the centre.

11.

Running the expansion backwards

One line of algebra turns Hubble law into an age, and the speed cancels out of it.

12.

One exam question, end to end

Twelve marks, four parts, no options: luminosity, temperature, radius, then a distance from the redshift.

13.

Astronomy and cosmology: quick revision

Reconnect stellar radiation, distance measurement, redshift and the evidence for cosmic expansion.

About the creator

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