# Chapter 9 Static electricity 9 1 static electricity

• Slides: 29

Chapter 9: Static electricity静电

9. 1 static electricity Static electricity is motionless charges that gathers on an object静电是聚集在物体上的静止电荷 9. 1. 1 electrification by friction The process of producing static electricity by rubbing is called electrification by friction 通过摩擦产生静电的过程称为摩擦带电

Fig 9. 4 the curving stream experiment The balloon rubbed with piece of fur cloth to the stream of water. The water stream is found curve away from its straight path. Why is so? The water stream and the balloon has opposite charges that attract each other

9. 1. 2 positive and negative charges Rub silk + Repel Rub silk + Rub fur -- Repel Rub silk + attract -- -- Rub fur 1. Ebonite硬木friction摩擦with fur毛皮produce negative charge 2. Glass玻璃friction摩擦with silk丝绸produce positive charge + & + (same charges)= repel击退 - & - (same charges) = repel击退 + & - (opposite charges) = attract吸引

Charges Action positive Repel Negative negative repel positive negative attract

Activity 3 Result: the strips spread out after rubbing Can you explain the phenomenon? The strips have same charges that make them repel from each other

Result: the hair will spread out and stand erect when the hand touches a metal body with static electricity. Discussion: Van de Graaff produce static electricity

9. 1. 3 Electroscope验电器 Is the device that is capable of detecting presence of charged object该设备是否能够 检测带电物体的存在

Metal plate

The gold leaf will diverge when charges flow in The gold leaf attach to metal when there is no charges flow in

• When a charged object touches the metal plate of or knob of electroscope, the charged conducted down to the needles or leaves. The needles or leaves will diverge发散 since they have the same charges that repel one another. • The diverge发散 is greater when the magnitude of charges is higher

9. 2 causes of electrification by friction • Electron= negative charge • Proton= positive charge • Neutron= no charge

Electricity is NOT created during rubbing • Electrons transferred from one object to another during rubbing/ friction

Triboelectric series is a lists that reflects the strength of substances to catch electron after they are rubbed against each other Can lose electron easily to become positive charged when rubbed with negative charged substance Stronger in capturing/gain electrons to become negative charged

9. 3 the applications and preventive measure for static electricity Static electricity is produced when we; - Stand - Walk - Put or take off clothes - Cutting - Stirring - Squeezing 9. 3. 1 the applications of static electricity静电的应用 1. The electrostatic air cleaner 2. The electrostatic spray painting 3. The electrostatic spraying of pesticides by crop duster

1. The electrostatic air cleaner can filter dust effectively a)Pre filter bigger dirt particles in air b) ionizer: charged dust particles c) Collector attract oppositely charged particles d) Charcoal absorb bad adour in air e) Clean air relased

2. The electrostatic spray painting (paint will evenly spread and reduce paint wastage) The surface is charged positive while the paint is charged negative The sprayed paint particles will then attracted by the positively charged surface and adhered胶合 on it surface Example: spray painting cars

3. The electrostatic spraying of pesticides 农药by crop duster作物喷粉(can increased even distribution 均匀 Jūnyún分布of the pesticide on the plants increase contact of the pesticide with the pest 害虫and inturn reduces the usage of pesticide 减少农药用量) ++ --

9. 3. 2 The Harm and precautions for static electricity静电的危害和注意事 项 1. Difficult to get rid of dirt on clothes made of blended fabrics as they are easily charged with static electricity混合面料制成的衣服容易带静电， 因此很难去除脏物 2. The standard purity of drugs in drugs manufacturing factories cannot be reached as static electricity attract dirt easily由于静电容易 吸引灰尘，因此无法达到药品制造厂中药品的 标准纯度 3. Sparks the static electricity can cause explosion of gas tank由于静电容易吸引灰尘，因此无法达到 药品制造厂中药品的标准纯度

4. Radio transmission may disturbed by static electricity resulted from friction between tyres abd the roads轮胎与道路之间的摩擦会导致静电干扰 无线电传输 5. In the process of weaving synthetic fibres, the friction between fibres and machine can result in loose weaving as the charged fibres repel each other在编织合成纤维的过程中，由于带电纤维 彼此排斥，因此纤维与机器之间的摩擦会导致编 织松散 6. Static electricity can be formed in the paper due to friction in the printing process. The pieces of paper cannot be arranged neatly and misprinting occurs由于打印过程中的摩擦力，纸张会形成静 电。纸张不能整齐地排列并且出现打印错误

To prevent harm caused by static electrictity防止静电造成伤害 1. Gas station attendant wearing pure cotton clothes加油站服务员穿着纯chún棉衣服 2. Computer maintenance technician wearing antistatic wrist straps电脑维修技术员穿着 防静电腕带

3. Plane tyres made of conducting rubber导电 橡胶制成的平面轮胎 4. Drag strips/metal chain金属链hanging at the back of road oil tanker悬挂在公路油轮背面的 拖条 To allow charges to flow into earth

conductor Insulator Electric charge move Electric charge can not freely move freely ( charges that can move freely in metals are the electron) Substance that can Substance do not conduct electricity easily Example: Metal, graphite, human Marble, rubber, glass, body, earth, acid, basic, plastic, alcohol, salt solution ceramic, pure water, oil

Van de Graaff Static electrical