1. Ultrasound and X rays- Imaging & Treating Ultrasound – longitudinal sound wave frequency above 20,000Hz. NON IONISING X ray – high frequency em wave with a wavelength about same size as diameter of atom. IONISING – this can cause damage to DNA in cells causing cancer/mutations Absorbed by metal and bone but transmitted by soft tissue, affect photographic film like light. Operators protect themselves behind screens that absorb x rays or limit exposure time. Ultrasound waves are partially reflected when they meet a boundary between two different media. The time taken for the reflections to reach a detector can be used to determine how far away such a boundary is.( Remember divide by 2 !) d = s x t Medical Applications Pre – natal scanning, removing kidney stones. CT Scans Adv – high resolution images image can be viewed from any direction (3D) Disad – mutate cells /kill cells Dental X rays Broken Bones – shadow pictures Killing Cancer Cells Film replaced by CCD’s means images can be transmitted electronically

2. Light – Structure and Function of the Eye Suspensory ligament Attach the cillary muscles to the lens RetinaLight sensitive cells – light to electricity IrisControls amount of light entering eye Cillary Muscles Focus light at different distances by changing the shape of the lens CorneaFocuses light LensFocus light from Diff distances onto retina Accomodation is the ability of the lens to change its shape to focus near and distant objects. The near point is approximately 25 cm and the far point is infinity. The film in a camera or the CCDs in a digital camera is the equivalent of the retina in the eye.

3. Lenses – The Refraction of Light A ray through the centre of the lens. A ray through the focal point. Put arrows on ! Is it real or virtual, magnified or smaller, upright or inverted ? P= power of the lens measured in dioptres (D) f is the focal length in metres Having materials with higher refractive indices means that lenses can be made thinner and lighter

4. Turning Forces – Balance and Stability Finding the Centre of Mass Pierce the card in at least two places. Suspend the card from one of these holes. Hang a plumb-line from the point of suspension. Using the plumb-line as a reference draw a vertical line on the card. Repeat for the other hole(s). The centre of gravity is where the lines cross on the card. The centre of mass of an object is that point at which the mass of the object may be thought to be concentrated. If freely suspended, an object will come to rest with its centre of mass directly below the point of suspension. If the line of action of the weight of an object lies outside the base of the object there will be a resultant moment and the body will tend to topple. T is in seconds f is in Hertz The time period just depends on the length not the mass Wider base & lower centre of mass means more stable ( less likely to topple if pushed)

5. Turning Forces – Moments The turning effect of a force is called the moment. M = moment in Nm or Ncm F is force in Newtons d is perpendicular distance in cm or m If balanced the sum of the clockwise moments = sum of anticlockwise moments Levers are force multipliers!

6. Forces – Hydraulics and Circular Motion Liquids are virtually incompressible, and the pressure in a liquid is transmitted equally in all directions. P = pressure in Nm -2 or Ncm -2 or Pa F is force in Newtons A is X sectional area in cm -2 or m -2 Pressure at A = 30/0.2 = 150 Nm -2 This is the same as the pressure at B So F = P x A = 150 x 1 = 150N It’s a force multiplier When an object moves in a circle it continuously accelerates towards the centre of the circle. This centripetal acceleration is because the objects velocity is changing because its direction is changing. Acceleration is the rate of change of velocity. The centripetal force ( resultant force) needed to make an object perform circular motion increases as: ■ the mass of the object increases ■ the speed of the object increases ■ the radius of the circle decreases. Centripetal force can be provided by: Friction Gravity Reaction force Tension

7. Motor Effect Creating a Force How it worksApplications Current through a wire Creates a magnetic field around it This interacts with the permanent magnetic field Producing a force A bigger force can be made by having: Stronger magnets Larger current When current changes direction…. the current (in the coil) creates a magnetic field (around the coil) so the magnetic field of the coil interacts with the (permanent) magnetic field of the magnets

8. The Transformer Inducing a Voltage How it worksCalculations a.c current in primary coil Causes a changing magnetic field in the core This induces an ac voltage in the secondary Coils made from copper because low resistance so does not get as hot. Coils are insulated to prevent short circuit. Soft iron magnetises and demagnetises easily Step up and step down ! Switch mode use higher frequency, less current when no load Put the numbers in first ! Power in = power out Assuming 100% efficient Only works with ac

9. Electromagnetism Applications The Relay – Used to switch on a more powerful circuit Current flows in the electromagnet and creates a magnetic field The electromagnet attracts the iron armature Which closes the switch gap The Loudspeaker – A changing force to create sound the current flowing through the coil) creates a magnetic field this magnetic field interacts with the perm mag field this produces a (resultant) force when the direction of the current changes, the direction of the force changes The Transformer– Changing voltage and current a.c current in primary coil Causes a changing magnetic field in the core This induces an ac voltage in the secondary

10. How Science Works Conclusions Write a statement that uses what’s written on the graph axes or At the top of a column in a table. The higher the altitude the longer the period of orbit. Look to see if you can comment on rate of change. How could the data/Experiment be Improved ? Increase range of …….. Use a smaller interval in the …….. Interpreting graphs To describe the graph write a statement that includes what is written on both the axes. Include any comments about rate of change. Identify any maximum or minimum and say what value on the x axis they are. If there are two lines then one mark will be for comparing what they show.

11. A student used the apparatus shown in the diagram to investigate how the weight supported by an electromagnet depends on: the current, I, flowing through the wire the number of turns of wire, n, wrapped around the iron core. How Science Works Conclusions for all values of n weight supported increases with increasing current but not linearly for a given current the weight supported increases with increase in n weight supported reaches a maximum with n = 30 turns