Explain how ultrasound builds up a picture of the inside of the body.

A pulse is partly reflected at each boundary between tissues, and the time each reflection takes to return gives the depth of that boundary.

What can infrared radiation reveal about the body?

It shows differences in surface temperature, so a thermal image can reveal inflammation or poor blood flow.

Explain how gamma rays are used to see inside the body.

A substance that emits gamma rays is given to the patient, and a camera outside the body detects the gamma rays that pass out, showing where the substance has collected.

OCR GCSE Physics A J249

Electricity

Topic overview Charge, and producing static electricity Transfer of electrons, and electric fields Current as a rate of flow of charge Charge, current and time Series and parallel circuits, and circuit symbols Current, potential difference and resistance Resistors whose resistance changes, and investigating them Linear and non-linear circuit elements from graphs Net resistance in series and parallel Circuits for measurement, and electrical power

Energy

Topic overview Conservation of energy, and energy stores Energy changes on heating, and calculating them Energy of a moving body, a spring and a raised object Dissipation, and energy transfer in domestic devices Power ratings, efficiency, and increasing it Reducing unwanted energy transfer, and the rate of cooling

Forces

Topic overview Measuring distance and time, and calculating speed Converting units, and rates Vectors and scalars in motion Distance-time and velocity-time graphs Average speed, and the equations of uniform motion How objects interact, and forces as vectors Newton's first law Resolving forces, and free body diagrams Resultant forces, and balanced forces Newton's second law, and inertia Momentum, and force as a change in momentum Work done, and stored energy Power, and Newton's third law Circular motion and changing velocity Stretching, bending and compressing; elastic and plastic Force and extension, linear and non-linear The spring constant, and work done in stretching Gravitational fields, weight and free fall Calculations with weight and gravitational field strength Turning forces and the moment of a force Levers and gears Pressure in fluids, and the force on a surface

Global Challenges

Topic overview Typical speeds and everyday accelerations Reaction time, stopping distance and the dangers of large decelerations Estimating stopping distances and the forces in a collision Energy resources, and trends in their use The national grid, and step-up and step-down transformers Why the national grid is efficient, and the transformer equation Mains electricity: a.c., d.c. and the domestic supply Live, neutral and earth wires, and electrical danger Red-shift and the Big Bang The formation of the Sun, and radiation from bodies The solar system Circular orbits and stable orbits Radiation and the temperature of a body, and seismic waves and sonar

Magnetism and Magnetic Fields

Topic overview Permanent and induced magnets, and magnetic poles Magnetic fields, and the dipping compass The magnetic effect of a current, and solenoids The motor effect and Fleming's left-hand rule The force on a conductor, and how a motor turns Induced potential, alternators and dynamos Transformers and the turns ratio The microphone

Matter

Topic overview How the atomic model changed, and the structure of the atom The size of atoms, and defining density Density of the states of matter, and density calculations Conservation of mass in changes of state Heating a system, and specific heat capacity Calculations with specific heat capacity and latent heat Gas molecules, temperature and pressure Compressing a gas, and changing its volume Doing work on a gas Atmospheric pressure and why it varies with height Floating, sinking and pressure in a liquid

Radioactivity

Topic overview Protons, neutrons and isotopes Unstable nuclei and the emissions they give out Balancing nuclear equations Electron energy levels, and radiation from atoms Half-life and the randomness of decay Penetration of alpha, beta and gamma Contamination and irradiation, and half-life as a hazard Uses of nuclear radiation Nuclear fission and fusion

Waves in Matter

Topic overview Amplitude, wavelength, frequency and period The wave equation Transverse and longitudinal waves Sound crossing a boundary; reflection, transmission and absorption Converting sound to vibrations, and the range of hearing Modelling waves with ripples and sound Electromagnetic waves as transverse, and energy transfer Frequency and wavelength across the spectrum What our eyes detect, and light as an electromagnetic wave Uses of electromagnetic waves Hazards of ultraviolet, X-rays and gamma rays Exploring structures with waves, and producing radio waves Absorption, transmission, refraction and reflection Ray diagrams for reflection and refraction How colour arises

Waves in Matter

Exploring structures with waves, and producing radio waves

3 things to know
Paper 4

Overview

How differences in absorption, reflection and speed let waves explore hidden structures, imaging the body with X-rays, ultrasound, infrared and gamma rays, why ultrasound suits an unborn baby but not the brain, and how radio waves are produced and received by oscillating charges in aerials and tuned circuits.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Explain why waves can be used to explore structures that cannot be seen directly.

Key term

Explain why bones appear pale on an X-ray image.

Key term

Explain why ultrasound rather than X-rays is used to scan an unborn baby.

Questions from this subtopic

Each one with the model answer underneath.

1
Explain why waves can be used to explore structures that cannot be seen directly.
Model answer
Different materials absorb, reflect and transmit waves by different amounts and the waves travel at different speeds in them, so the waves that come back reveal where the boundaries are.
2
Explain why bones appear pale on an X-ray image.
Model answer
Bone absorbs X-rays far more strongly than the soft tissue around it, so fewer X-rays reach the detector behind the bone.
3
Explain why ultrasound rather than X-rays is used to scan an unborn baby.
Model answer
Ultrasound is not ionising, so it does not risk damaging the cells of the baby as X-rays would.
4
Explain how ultrasound builds up a picture of the inside of the body.
Model answer
A pulse is partly reflected at each boundary between tissues, and the time each reflection takes to return gives the depth of that boundary.
5
What can infrared radiation reveal about the body?
Model answer
It shows differences in surface temperature, so a thermal image can reveal inflammation or poor blood flow.
6
Explain how gamma rays are used to see inside the body.
Model answer
A substance that emits gamma rays is given to the patient, and a camera outside the body detects the gamma rays that pass out, showing where the substance has collected.

See the rest and revise

Other ways to work this

The same content, four other ways.

What is inside Levo

Six ways to work the same material.

1Closed book

2Open book

3Closed book

The 3-step method, run for you

Answer cold, learn it, then prove it stuck. Levo tracks the jump between your first attempt and your last.

Electricity

Energy

Forces

Global Challenges

Cram a whole paper in one sitting

Sort every topic into what you know and what you do not, then drill only the weak ones.

Mass × .

velocityaccelerationweight

Blank Blitz makes facts automatic

Rapid timed gap-fills on the terms and numbers you need to recall without thinking.

AGamma radiation is the most penetrating.

BAlpha radiation is the least penetrating.

CAlpha radiation is the most strongly ionising.

Build It gets the exam shape right

Assemble a full-mark answer from its marking points, in the order an examiner wants them.

Current means the rate of flow of electric charge.

TrueFalse

Test It catches misconceptions

Spot the fault in a statement. The traps are the mistakes students actually make.

721941163128510

Brain Breaks between sessions

Short focus games to reset attention, so the next set lands better than the last.

Every question in Waves in Matter, on a schedule.

Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.

Start revising, £5 a month See how the method works

Or £46 a year, about £3.83 a month. Cancel anytime.