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# Teacher's Notes

The Activities are designed for Key Stage 3 pupils. However, the Extension material is suitable for Key Stage 4.

### 1. Projecting the Light - Reflection

• A 12V lamp would be ideal but a small 1.5V lamp in a holder could be used.
• Pupils should try to vary the angle between the mirrors.
• A curved reflector can be made from a strip of cardboard about 30cm x 10cm covered with smoothed aluminium foil.
• Pupils may have realised that a 'catoptric' system would be best, i.e. the lamp placed at the focus of a parabolic reflector.
• The observations are subjective so results will vary.

Extension - Pupils could:
• use a light sensor to measure the light output for objective data
• measure the focal length for differently shaped reflectors and compare the brightness of the light for each. Is there a relation?

To find the focal point of a curved reflector, pupils need to:
• draw round the outline
• draw in at least 3 parallel lines
• mark in normals where each line touches the outline of the mirror
• measure the incident angle
• hence draw the reflected rays
• their intersection will be the focus.

### 2. Projecting the Light - Refraction

Experiment a)
• Pupils could also try the 'appearing coin' trick, i.e. pour water into the beaker so the coin appears.
• They will need a piece of card to hide the coin from view at first.
• Ray diagrams should be used to explain what is happening.
Extension - Pupils could:
• estimate the apparent depth of the coin, measure the real depth
• Real depth / Apparent depth = Refractive Index, i.e. amount of refraction (about 1.3 for water).
Experiment c)
• Probably best as a demonstration using flat sided prisms face down on the bench.
• Prisms should behave like a lens, i.e. should see light converging (Fresnel used a combination of prisms and a lens in his system).
Extension - Pupils could:
• measure focal length of differently shaped convex lenses by approximate method, i.e. hold up to light source with paper screen at the back Focal length = distance of lens to screen when a sharp image is obtained
• explain how a convex lens can correct long sight
• make a telescope using 2 convex lenses stuck with plasticine onto a metre rule and separated by distance f1 + f2 as shown.

### 3. Solar Power

If you haven't got a solar panel made up, it is not too difficult to construct one:
• Take a piece of hardboard about 50cm square.
• Line it with bubble-wrap or other insulation.
• Cover this with some black plastic.
• Get some rubber tubing (that can fit onto the cold water tap) - about 2m or 3m in length. Leaving about 30cm at either end, bend the tubing into S-shaped loops and use some string to keep the loops together.
• The tubing should be placed onto the black plastic and a sheet of perspex or glass also about 50cm square placed over this. Some parcel tape can be used to keep the assembly together.
• It only remains to connect one end of the tubing to a cold water supply and the other end into a beaker or bowl.

Extension - Pupils could:
• use the Internet to research solar power - find out where solar power is used and how a solar power station works.

### 4. Satellites

The answers to the questions are:
• Gravity or gravitational force
• The Moon
• Landsat (for survey and mapping) and Tiros or Meteosat (for weather monitoring) are well-known ones. There a number of sources that mention these, e.g. Starting Science Book 3 and Encarta.
• 300 million x 0.1 = 3 x 107 m = 3 x 104 km ยท GPS stands for Global Positioning System; GPS enables sailors and anyone on the ground to find their position within 100m - sailors can also compute their latitude, longitude, course and speed.
• Satellites have large solar panel "wings"; these transfer solar energy into electrical energy.

Solar energy is available all the time, it won't run out, it does not cause pollution, it doesn't use up valuable fossil fuels, and it's free.

Extension - Pupils could use the Internet to find out:
• the names of the major equatorial orbiting satellites, why they are said to be geosynchronous, and what they are used for
• what two frequencies the carrier signals of GPS satellites transmit on (they are 1575MHz and 1228MHz) and why it is strongly advised that DGPS should not be relied upon by itself for navigation (interference can cause loss of signal).