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P3 topic 1 (part i) Radiation in treatment and medicineThis topic looks at:•Radiation in medicine•How eyes work

Fill in how each type of radiation forms an image and where it is used.

Label the pupil, cornea, lens and retina of the eye on the diagram.

Intensity is the power of the incident radiation divided by the area over which it is spread. Intensity = power of incident radiation / area

I= P/A

Power is measured in watts, intensity in watts per square metre W/m2

1.Calculate the intensity of a 100W torch beam spread over an area of 20cm2.

2.Calculate the intensity of a laser pointer with 1.0 x 10 -3 W on an area of 5mm2.

3.If the intensity of a torch’s beam is 12W/m2 over an area of 4m2 what is the power output of the bulb?

Describe uses for ionising and non-ionising radiation.

Definitions

1)Define ‘far point’

2) Define ‘near point’

What is ‘ionising’ radiation?

Radiation detected

How it forms an image

Where it is used

Visible light

X-rays

Gamma rays

UltrasoundPeople can focus on images close to them and images far away. Explain the role of the ciliary muscles which enable them to do this.

Practice 6 mark question:Explain what happens to light when it enters the eye.

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P3 topic 1 part (ii) Radiation in treatment and medicineThis topic looks at:•Sight problems•Different lenses

Explain the process of laser correction.

6 mark practice. Describe how vision can be corrected by wearing glasses. Use diagrams.

Describe what is meant by ‘long sight’.

Describe what is meant by ‘short sight’.

The lens equation

1/f = 1/u + 1/v (f = focal length, u = object distance, v = image distance) all in metres.

1)If an object is 20cm away from a lens with a focal length of +5cm, where will the image be?

2)An object is 8 cm away from a converging lens with a focal length of #=20cm. Where will the image be? What tells us the image is virtual?

The power of a lens is measured in dioptres.Power of lens = 1/focal length (in metres)

1)What is the power of a lens with a focal length of (i)50cm (ii) 0.7m (iii) 4 cm2) If the power of the lens in a child’s eye is 15D, what is the focal length?3) Cormorants have a greater power of lens that any other bird with 50 dioptre. What is their focal length?

Explain what is meant by virtual image and real image.

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P3 topic 1 part (iii) Radiation in treatment and medicine

This topic looks at:•Reflection and refraction•Critical angle

Refraction

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Reflection

Describe the relationship between the angle of incidence and the angle of reflection when a light ray hits a mirror.

Refractive index – Snell’s lawThe speed of light is determined by the material (or medium) through which it travels. As it leaves one medium and enters another, it changes speed and so refracts. The refractive index is the extent to which light is refracted when it enters a medium. It is calculated as:

Where: n is the refractive index of the mediumi is the angle of incidencer is the angle of refractionA refractive index has no units. Air has an index of 1.0, water is 1.3 and many types of glass are around 1.5. This means that light travels 1.3 times as fast in air than it does in water, and 1.5 times as fast in air than in glass.

Explain what total internal reflection is.

A light ray travelling from water to air approaches the surface at an angle of 21 0 to the normal. If the refractive index of air is 1 and that of water is 1.3, what will the angle of refraction be?

What is meant by the critical angle?

Define refraction (use the key words medium and normal; and make sure you talk about the speed of the waves).

Explain, with diagrams, what happens when light crosses the interface from water to air.

On a separate piece of paper:

6 mark practice: Explain how automatic rain sensors on a car work, using the key terms ‘infrared sensor’ and ‘critical angle’

Longer answer practice: Explain how total internal reflection makes an instrument such as an endoscope possible

Extended writing practice: Explain how ultrasound waves can be used to break up a kidney stone, treat injured muscles and produce foetal scans. Include risks and benefits.