5 SAFE EXPERIMENTS USING A VAN DE GRAAFF! INSPIRING TOMORROW S SCIENTISTS THROUGH PRACTICAL SCIENCE

Transcription

1 5 SAFE EXPERIMENTS USING A VAN DE GRAAFF! INSPIRING TOMORROW S SCIENTISTS THROUGH PRACTICAL SCIENCE

2 INTRODUCTION THE VAN DE GRAAFF GENERATOR IS AMONGST THE MOST RECOGNISABLE PIECES OF APPARATUS IN THE SCHOOL SCIENCE LABORATORY, AND IN SCHOOL IT IS USED FOR DRAMATIC, MEMORABLE DEMONSTRATIONS INVOLVING ELECTROSTATICS AND VERY HIGH VOLTAGES. EVERY SCHOOL SCIENCE DEPARTMENT WHICH TEACHES ABOUT STATIC ELECTRICITY SHOULD CONSIDER PURCHASING A VAN DE GRAAFF. THERE ARE SEVERAL EXCITING AND STIMULATING ELECTROSTATIC DEMONSTRATIONS THAT CAN BE CARRIED OUT WITH THE VAN DE GRAAFF GENERATOR, BUT BECAUSE OF THE HIGH VOLTAGES INVOLVED (UP TO 30 KV) THERE IS AN AMOUNT OF TREPIDATION AMONG THOSE UNFAMILIAR WITH THEM. THIS GUIDE AIMS TO HELP OVERCOME THIS BY PROVIDING 5 SAFE AND EASY EXPERIMENTS THAT CAN BE CARRIED OUT WITH A VAN DE GRAAFF GENERATOR. READ ON FOR 5 SAFE EXPERIMENTS USING A VAN DE GRAAFF

3 HOW DOES THE VAN DE GRAFF GENERATOR WORK? A Van de Graaff generator consists of an insulating belt, driven by a plastic pulley, with an arrangement of metal combs at either end of the belt, that transports electrical charge to the dome. The charge is separated on the bottom of the belt due to the triboelectric effect as the belt separates from the bottom roller, charge is transferred to the belt which is taken up to and deposited to the dome. Similarly, as the belt separates from the top roller, it acquires charge opposite from that which it brought up, which is carried down to earth. When using a Van de Graaff generator it is quite likely that the user will receive a short shock by accidental or intentional contact with the charged dome. *CLEAPSS has revealed no recorded incident of direct injury caused by shocks from the correct use of school Van de Graaff generators. However, some people will be more sensitive to these shocks than others and for that reason it is recommended that only volunteers should take direct part in the practical work. IMPORTANT REMINDER: The Van de Graff generates electromagnetic signals, which can disturb electrical equipment. Therefore, individuals with pacemakers; cochlea implants, or any other such electronic device must not be within 6m of the DVDG when it is functioning. *Information taken from: Practical Physics.

4 MAKE LIGHTENING You can create mini lightning bolts with a Van de Graaff generator using a discharge sphere, which will vary from white-hot and quite intense sparks to red-purple and less intense sparks, accompanied by a crackling sound. Simply, switch on the generator and let it run for 2 minutes so that there is a build-up of charge and when the grounded discharge wand is brought near to the dome, lightening discharges will occur. Try varying the distance between the wand and the dome to see the different types of sparks. Under the best circumstances and depending on humidity conditions, sparks can leap up to 30cm. This demonstration is most effective and more impressive in a dark room!

5 The classic hair-raising experiment with the Van de Graaff and a favourite with many students! HAIR-RAISING As the generator will apply charge to its dome, it will also apply a charge to anything else that comes into contact with it. Should that object be a person, they obtain a net surplus of charge (be it positive or negative). It is especially noticeable with hair, as each individual strand is repelled from every other and from the scalp. To carry out this experiment, thoroughly discharge the generator before beginning and ensure that the volunteer stands on an insulating stool (FU91980). The volunteer should then place both hands upon the Van de Graaff dome; the operator can then switch on the dome and wait Your volunteer s hair will begin to levitate by electrostatic repulsion. Before the volunteer steps down, allow the generator motor to stop, and discharge the dome with the earthed rod. This experiment is most effective with a volunteer who has long blonde, clean and un-moussed hair. Darker hair can be too heavy, and short hair doesn t give the same dramatic effect. OFFER: Stuck for volunteers? Alternatively, you can use the brush of hair accessory in the Van de Graaff accessories kit! Click here for more information, or visit: timstar.co/vdgaccessories.

6 Using a Van de Graaff you can generate an electrical wind that is powerful enough to deflect a candle s flame. ELECTRIC WIND To carry out this experiment, attach a conductor, (a darning needle, for example) on the body of the collector dome, radially outwards, using clay to attach. Positive ions will rush towards the collector dome and neutralise their charges, whereas, negative ions move away (due to electrostatic repulsion) from the generator and do not get neutralised. The running generator will supply, at fast speed: negative ions, the ions running away form a wind called electric wind which blows away from the generator. By attaching the conductor or needle, you have created an electric wind. Light your candle, and hold it in front of the point the flame should lean away from the generator. To see how far the effect of wind extends, slowly move the candle away from the generator until the flame is no longer deflected. When generating Electric Wind, you can also turn a vane; generate statics; spin a spinner or rotate a collector dome.

7 FLYING OBJECTS Another exciting experiment involves foil cases flying! The electrostatic charge created by the Van de Graff goes through the foil cases and they repel each other and fly off due to their minimal weight. When they settle on the ground they release any remaining charge. To carry out this experiment, ensure the Van de Graff is discharged; place the foil cases upside down on top of the dome and switch on the generator. As they acquire charge they will start to fly off one-by-one. This experiment is most effective and more dramatic if different sizes of foil cases are used. Click here for more information or visit: timstar.co/vdg-foilcases

8 KINETIC THEORY Using a Van de Graaff you can show random motion of metallic balls continuously affected by repulsion and loss of charge within a transparent vessel. To carry out this experiment attach a transparent tube (filled with aluminum foil balls) to the top of the dome, switch on the Van de Graaff and watch the balls randomly move around the cylinder. This is also useful model to teach the random motion of particles in a fluid. To carry out this experiment we recommends using the Dancing Balls accessory in the Van de Graaff accessories kit! Click here for more information or vists: timstar.co/vdg-accessories.

9 WHY CHOOSE TIMSTAR? Every year Timstar provide quality equipment and resources to 5,000 education establishments worldwide, including 1,250 UK academies and we help 2.5million students worldwide to improve attainment in science. Over 5,000 queries are effectively handled to a positive outcome yearly by our in-house technical experts and our responsive customer service team is always dedicated to your needs. Every school that teaches about static electricity should consider purchasing a Van de Graff generator as it forms the basis for several demonstrations using additional equipment as discussed throughout this guide. TIMSTAR LABORATORY SUPPLIERS LTD. UNIT 12, ION PATH, ROAD THREE, WINSFORD INDUSTRIAL ESTATE, WINSFORD, CHESHIRE, CW7 3BX Website: If you require more information please do not hesitate to get in contact via the details to the right or click the link below for more information on our range of Van de Graaff generators. sales@timstar.co.uk Tel: Fax: CLICK HERE FOR TIMSTAR S RANGE OF VAN DE GRAAFF GENERATORS AND USEFUL ACCESSORIES, OR VISIT: timstar.co/vdgaccessories Connect with us: