simple lenses

Let's make some simple lenses and see how they bend light.

Caution: This activity uses hot water and a knife. Have an adult assist you with this activity.

What you need

To do this activity you will need:

·         a torch

·         a comb

·         two packets of jelly crystals, both the same flavour and preferably a light colour or clear. In some parts of the world, jelly is called jello.

·         a rectangular plastic container, such as a lunch box, to use as a jelly mould

·         hot water

·         a spoon

·         a fridge

·         a dark room

·         a knife with a straight edge

·         a cutting board

·         a table

·         an adult.

What to do

1. Mix up your jelly, but only use half as much water as normal. You need to make very stiff jelly.
2. Pour the jelly into your mould and leave it to set overnight.
3. When the jelly has set, tip it out onto the cutting board. It is easier to tip out if you run a knife around the edge and then dip the outside of the mould into warm water for about ten seconds.
4. Use the knife to cut the jelly into the shape of some lenses such as:
   ·         wide in the middle and thin at the ends
   ·         thin in the middle and wide at the ends
   ·         semicircular.
5. Shine light from the torch through the lenses and look at how they bend the light. If you place a comb between the torch and the lenses, you will get lines of light, which can make it easier to see the light bending.
6. After you have finished, you can eat the jelly.

What's happening

When light hits a boundary between two substances, like the surface of the jelly, it often bends. This is called refraction. When light goes from air into the jelly, it bends away from the surface of the jelly. When it goes from jelly into the air, it bends towards the surface of the jelly. When the jelly surface is curved, rays of light hitting at different spots on the surface will either spread out or move together.

If the jelly makes a concave lens (thick on the ends, thin in the middle) the rays of light will be spread out.

If the jelly makes a convex lens (thin on the ends, thick in the middle) the rays of light will bend towards each other, until they cross over and then spread out again. If you are lucky and your lens is just the right shape, you may even find the rays of light all cross over at one spot.

The strength of a lens depends on its shape and the material it is made from. Different materials will bend light by different amounts.

The soap-propelled boat

Make a boat that uses detergent to move through the water and learn about surface tension.

What you need

To do this activity you will need the following:

• thick cardboard or thin plastic (like the lid of a margarine container)
• scissors
• a large shallow bowl or a baking dish full of water
• dishwashing liquid
• a toothpick, pencil or eye dropper.

What to do

1. Carefully cut out a boat shape from the cardboard (around 8 centimetres long by 6 centimetres wide).
2. Cut out a triangular notch at the back of the boat with the triangle pointing towards the back of the boat.
3. Gently place the boat on the water in the dish.
4. Using the pencil, toothpick or dropper, place a drop of detergent into the notch at the back of the boat.
5. Watch your boat zip across the water!

What's happening?

It looks like the boat is being pushed along by the detergent, but in fact it is being pulled by the water in front of it.

In many liquids, the molecules of the liquid are attracted to each other. This attraction makes the surface of the liquid act like a stretched-out balloon skin. Any point on the surface of a liquid is under tension. In water, the tension is only very slight and it is fairly easy to break through the surface, but if you have ever done a 'belly-flop' into a swimming pool, you have felt the effect of surface tension.

Different liquids have different amounts of surface tension. A mixture of water and detergent (or soap) has much less surface tension than water.

Normally, surface tension pulls the boat in every direction.

When you add the detergent, the surface tension at the back is reduced. The tension at the front pulls the boat forward. The triangular notch helps the boat drag a little bit of the detergent with it, so it travels further.

You may find the boat only works once or twice. This is just because the water mixes with the detergent you have dropped in, so the surface tension of the water in the container is reduced and it can't pull the boat as well.

Kaleidoscope

Follow these instructions to make your own kaleidoscope and have fun with reflections.

The word kaleidoscope means 'seeing beautiful shapes'. Images of the outside world pass through a kaleidoscope to your eye but they change on the way. Through lenses and mirrors, the kaleidoscope bends and distorts light waves.

What you need

To make your own kaleidoscope you will need to gather:

• three rectangular pieces of mirror or mirrored cardboard cut to the same size (about 15 cm long and 4 cm wide)
• some tape
• greaseproof, tracing or baking paper
• plastic kitchen film or an overhead transparency sheet
• scissors
• sequins, confetti or coloured paper.

What to do

1. Tape the mirrors together along the long sides to form a triangular tube with the mirrored surfaces on the inside. It's easiest if you leave a two millimetre gap between each mirror.
2. Cover one end of the tube with greaseproof, tracing or baking paper. Secure this with tape.
3. Place the confetti, sequins or very small pieces of coloured paper onto the outside of the paper.
4. Stick a piece of clear plastic film or transparency on the very outside over the small coloured pieces to ensure they will not escape.
5. Point the kaleidoscope down at a bright light source. While looking through the viewing hole, rotate the kaleidoscope so the confetti or sequins move about. You will see beautiful shapes that constantly change.
6. You can experiment with different coloured cellophane filters, or increase the number of mirrors used to build the tube.

What's happening

A kaleidoscope is made from mirrors placed at angles to each other. The viewer looks in one end and light enters the other end. This light is reflected again and again by the mirrors.

Light bounces off a surface at exactly the same angle at which it hits the surface. As the tube is rotated, the tumbling coloured objects present the viewer with varying colours and patterns. These show up as symmetrical patterns due to the reflections in the mirrors. When the mirrors are set at 60 degree angles, it creates six sets of reflected images.

Jelly optics

Follow these instructions to make your own jelly lenses and have fun with bending light.

Let's make some simple lenses and see how they bend light.

Caution: This activity uses hot water and a knife. Have an adult assist you with this activity.

What you need

To do this activity you will need:

• a torch
• a comb
• two packets of jelly crystals, both the same flavour and preferably a light colour or clear. In some parts of the world, jelly is called jello.
• a rectangular plastic container, such as a lunch box, to use as a jelly mould
• hot water
• a spoon
• a fridge
• a dark room
• a knife with a straight edge
• a cutting board
• a table
• an adult.

What to do

1. Mix up your jelly, but only use half as much water as normal. You need to make very stiff jelly.
2. Pour the jelly into your mould and leave it to set overnight.
3. When the jelly has set, tip it out onto the cutting board. It is easier to tip out if you run a knife around the edge and then dip the outside of the mould into warm water for about ten seconds.
4. Use the knife to cut the jelly into the shape of some lenses such as:
   • wide in the middle and thin at the ends
   • thin in the middle and wide at the ends
   • semicircular.
5. Shine light from the torch through the lenses and look at how they bend the light. If you place a comb between the torch and the lenses, you will get lines of light, which can make it easier to see the light bending.
6. After you have finished, you can eat the jelly.

What's happening

When light hits a boundary between two substances, like the surface of the jelly, it often bends. This is called refraction. When light goes from air into the jelly, it bends away from the surface of the jelly. When it goes from jelly into the air, it bends towards the surface of the jelly. When the jelly surface is curved, rays of light hitting at different spots on the surface will either spread out or move together.

If the jelly makes a concave lens (thick on the ends, thin in the middle) the rays of light will be spread out.

If the jelly makes a convex lens (thin on the ends, thick in the middle) the rays of light will bend towards each other, until they cross over and then spread out again. If you are lucky and your lens is just the right shape, you may even find the rays of light all cross over at one spot.

The strength of a lens depends on its shape and the material it is made from. Different materials will bend light by different amounts.

source: http://www.csiro.au/Portals/Education/Programs/Do-it-yourself-science/Physical-sciences-activities.aspx

Charge your light bulbs

Charge your light bulbs

Safety: Be careful with the fragile fluorescent lights bulbs or tubes in the dark. Make sure you have shoes on.

What you need

• Fluorescent light bulb or tube
• Balloon
• Full head of hair 

What to do

1. Darken the room.
2. Hold the fluorescent bulb in one hand and the balloon in the other. Rub the balloon vigorously on your hair.
3. Bring the balloon near the bulb and watch what happens.
4. Move the balloon up and down the bulb without touching the bulb.
5. Move the balloon slowly toward the glass until it almost touches and see if you can get a spark to jump.

What's happening?

An electron is a particle of an atom with a negative electrical charge.

Electrons orbit the nucleus of an atom. The flow of electrons produces electricity.

Electrons are relatively free to jump from one atom to the next, and they are attracted to some materials more than others.

A fluorescent bulb produces less heat, so it is much more efficient.

When you rub a balloon on your hair, electrons from your hair jump over to the balloon.

A fluorescent bulb is a type of light that uses electricity to excite mercury vapor contained inside the bulb. The result is short-wave ultraviolet light.

This light then causes the white coating on the inside of the light, which is made up of phosphors, to fluoresce producing visible light.

Phosphors are substances that give off visible light when exposed to light or radiation.

Bringing a negatively charged balloon near a fluorescent tube excites the electrons in the mercury vapour.

This also happens when you connect the bulb to an electrical current.

Electrons in the mercury move to higher energy orbits and when they drop back down to their normal orbit they give off energy.

This energy is in the form of ultraviolet light and cause the phosphors (white coating) to glow.

When a spark jumps, you get a big release of energy and a correspondingly brighter glow.

Applications

A fluorescent bulb is more efficient than a regular (incandescent) light bulb because they use less electricity to produce the same amount of light.

The basic idea behind regular light bulbs is simple:

• Electricity runs through the filament.
• The filament resists the electricity, and this resistance turns electrical energy into heat.
• The heat is enough to make the filament white hot, and the "white" part is light.
• The filament glows because of the heat. 

The problem is that heat wastes a lot of electricity. Heat is not light, and the purpose of the light bulb is light, so all of the energy spent creating heat is a waste.

A fluorescent bulb produces less heat, so it is much more efficient.

A fluorescent bulb is four to six times more efficient than incandescent bulbs.

It's a good idea to buy energy efficient light bulbs for your entire house.

They can save you money on your electricity bill, they produce just as much light as standard bulbs and they last longer and don't have to be replaced as often as standard bulbs.

Phosphors are used in many other items, including regular TVs and plasma screens.

TOP DIVER

What you need

• 1 L or 2 L plastic bottle
• Water
• Plastic pen top
• Piece of Blu Tack or similar
• Hook (optional)

What to do

1. Fill the plastic bottle to the brim with water.
2. Stick a small piece of Blu Tack onto one end of the pen top as in the diagram.
3. Put the pen top into the bottle. The Blu Tack weighs down one end so that the top stays upright with a bubble of air inside.
4. Seal the bottle tightly and squeeze the sides of the bottle.

If you squeeze hard enough, the pen top sinks. Stop squeezing and it rises. Squeeze just the right amount and you can get the top to hang in the middle of the bottle.

What's happening

This is a demonstration of buoyancy. The top floats because it, and the bubble of air trapped in it, displace a greater weight of water than it weighs itself.

When you squeeze the sides of the bottle, you put pressure on the air trapped in the top causing it to shrink in volume. The top and trapped air now displace less water and weigh more than the water.

Try adding a hook to the Blu Tack and use your top diver (also referred to as a cartesian diver) to lift objects off the bottom of the bottle.

SOURCE: http://www.csiro.au/Portals/Education/Programs/Do-it-yourself-science/Physical-sciences-activities/cartesian-diver-activity.aspx