1. Applications
1.1. Photocopier
1.2. Ink jet printer
1.3. Laser Printer
1.4. Potential Hazards
1.4.1. Lightning
1.4.1.1. How it happens
1.4.1.1.1. Thunderclouds carry electric charges. If, say, a negatively charged thundercloud passes over a building, positive charges are induced on the roof, and the force of attraction between the opposites charges may be strong enough to attract the electrons and produce a sudden flow of electrons from cloud to roof. In other words, the roof may be struck by lightning.
1.4.1.1.2. Lightning is caused by the buildup of electrostatic charge in clouds. One region (the top) within the clouds the cloud builds up a positive charge and the other region (the bottom) builds up a negative charge.
1.4.1.2. The lightning conductor
1.4.1.2.1. A tall building is protected by a lightning conductor.
1.4.1.2.2. It consists of a thick copper strip. The lower end of the strip is attached to a metal plate in the ground; the upper end of the strip is attached to sharp spikes
1.4.1.2.3. The lightning conductor reduces the risk to the building in two ways:
1.4.1.3. The base of a storm cloud is negatively charged. The figure belows shows the cloud above flat ground. The cloud causes the ground beneath to become positively charged. Explain, in terms of the particles involved, how the ground becomes positively charged.
1.4.1.3.1. Like Charges repel so electrons in the ground repelled by cloud leaving grounds positively charged.
1.4.2. Fires and explosions
1.4.2.1. Pumping of oil into aircrafts
1.4.2.2. Truck Carrying flammable substances
1.5. State on example where static electricity is useful.
1.5.1. Photocopier
1.5.2. Inkjet Printer
1.5.3. Electrostatic precipitator to clean the air
2. Electric Field
2.1. Definition
2.1.1. A region in which charged particles experiences an electric force
2.2. Determine direction of field
2.2.1. Positive test charge used
2.2.2. Draw field lines represent electric field
2.2.3. Arrow
2.2.3.1. Direction movement positive test charge
2.3. Properties of electric field lines
2.3.1. 1. Field lines originate in and leave positive charges, and they enter and end in negative charges
2.3.2. 2. The number is proportional to the magnitude of the charge.
2.3.3. 3. Field lines are closer together where the electric field is largest/strongest.
2.3.4. 4. Where field lines are far apart, the electric field is smallest/weakest.
2.3.5. 5. The field lines of the like charges do not cross one another, which produces repulsive forces.
2.3.6. 6. The field lines of the unlike do not cross one another, which produces an attractive forces.
2.4. Strength
2.4.1. Closer
2.4.1.1. Stronger
2.4.2. Further
2.4.2.1. Weaker
2.5. A charged droplet held stationary by a vertical electric field.
2.5.1. The atomizer produced a fine spray of oil droplets. The droplets are negatively charged.
2.5.2. If the droplet is negatively charged, it can be held stationary by applying a voltage across the metal plates where the upper plate is positive. Explain Why
2.5.2.1. The electric force should be pointing up so the upper plate is positively charged
2.5.3. When the droplet was stationary, the electrostatic force pointing up is equal to the weight of the droplet pointing down so the net force acting on the droplet is zero
2.5.4. State and explain what would if the stationary oil droplets starts to evaporate.
2.5.4.1. The mass/weight of the oil droplet decreases.
2.5.4.2. The electrostatic force acting upwards becomes greater than weight of the drop.
2.5.4.3. The drop accelerates upwards.
2.5.5. If the droplet is positively charged, it can be held stationary by applying a voltage across the metal plates where the upper plate is negative. Explain Why.
2.5.5.1. The electric force should be pointing up so the upper plate is negatively charged.
3. Fibers
3.1. Synthetic
3.1.1. e.g. Nylon & Polyester
3.1.1.1. Loosely bound electrons
3.1.1.1.1. Small amount of heat
3.1.1.1.2. Energy is produced by friction during rubbing which is enough to remove the electrons
3.1.2. So easy to charge by rubbing
3.2. Natural
3.2.1. e.g. Cotton & Wool
3.2.1.1. tightly bound electrons
3.2.1.1.1. Large amount of heat energy is needed to remove the electrons
3.2.2. So difficult to charge by rubbing
4. Electric Charge
4.1. Atom
4.1.1. Electrically Neutral
4.1.2. Contains
4.1.2.1. Neutron
4.1.2.2. Proton (+)
4.1.2.3. Electron (-)
4.1.2.3.1. Gain
4.1.2.3.2. Lose
4.2. Charge
4.2.1. Unlike
4.2.1.1. Attracts
4.2.1.2. Example
4.2.1.2.1. Positive-negative
4.2.2. Like
4.2.2.1. Repels
4.2.2.2. Example
4.2.2.2.1. Negative-Negative
4.2.2.2.2. Positive-Positive
4.2.3. Measured in
4.2.3.1. Coulumbs
4.2.3.1.1. Positive Charge
4.2.3.1.2. Negative Charge
4.2.3.1.3. 1 microcoulomb=10^-6
4.3. Detecting Charge
4.3.1. You can detect electric charge using a leaf electroscope
4.4. Law of Conservation of Charge
4.4.1. Charge cannot be created or destroyed
4.4.2. Charge can be transferred from one object to another
5. Methods of Charging
5.1. Friction
5.1.1. Charging an insulator by friction
5.1.1.1. Friction
5.1.1.1.1. Rubbing
5.1.1.2. Insulator
5.1.1.2.1. Electrons are not able to flow within it
5.1.1.2.2. e.g. glass, dry wood, most plastics, cloth, and dry air
5.1.1.3. How does it work
5.1.1.3.1. Two objects rubbed together
5.1.1.4. Discharging charged insulators
5.1.1.4.1. Heating
5.1.1.4.2. Humid Conditions
5.1.2. Problems caused by friction or rubbing
5.1.2.1. Ribbon of cassette and head get charged and attract the dust particles
5.1.2.2. Body of the plane gets charged by friction with air
5.1.2.3. Belts moving on the wheels of machines get charged
5.1.2.4. Duster and board get charged while cleaning the board by the duster
5.1.2.5. Doctors in operation theatre do not wear nylon clothes but they wear cotton clothes because nylon can easily be charged unlike cotton.
5.1.2.6. Sometimes charges produced, collide with each other producing spark
5.1.3. As a boy slides down a plastic slide, he becomes charged and his hair stands on the end.
5.1.3.1. (i) Explain why the boy's hair stands on the end
5.1.3.1.1. The boy becomes charged because of friction between the slide and his clothes.
5.1.3.1.2. As the boy travels down the slide, the slide loses electrons and becomes positively charged. The hair gains electrons and becomes negatively charged
5.1.3.1.3. All the hairs have the same charge
5.1.3.1.4. Same charges repel.
5.1.3.2. (ii) The boy grabs hold of a metal post and his hair falls back down. Explain why his hair falls back down.
5.1.3.2.1. Metal post is conductor of electricity
5.1.3.2.2. Charge is earthed/charge flows to ground
5.1.3.2.3. Discharging hair
5.1.3.2.4. Hair falls down due to its weight
5.1.4. Electrostatic charges can be placed on objects by friction.
5.1.4.1. State the name of the charged particle that is transferred from one object to another in this process
5.1.4.1.1. Electrons
5.1.5. A cleaner is attempting to remove dust from some plastic-covered furniture, using a dry cloth. Unfortunately, this seems to make the dust cling more firmly to the plastic covering.
5.1.5.1. (i) Suggest why this happens.
5.1.5.1.1. Plastic/furniture becomes charged by friction
5.1.5.1.2. Electrons transfer from furniture to cloth (or cloth to furniture).
5.1.5.1.3. Plastic/furniture attractss dust/fluff
5.1.5.2. (ii) Suggest why this would be less likely to happen if the cleaner used a cloth which was very slightly damp.
5.1.5.2.1. Idea of charge leaking because water is a conductor
5.2. Induction
5.2.1. Charging a conductor by Induction
5.2.1.1. Charging without coming into direct contact
5.2.1.2. Conductor
5.2.1.2.1. Electrons free to move within it
5.2.1.2.2. Metals, plasma, and graphite
5.2.1.2.3. Connected to ground wires
5.2.1.3. Steps
5.2.1.3.1. 1. Take a neutral conducting sphere
5.2.1.3.2. 2. Bring a negatively charged rod near (but not touching) the sphere
5.2.1.3.3. 3. This creates a charge imbalance on the sphere, due to repulsion from the charged rod.
5.2.1.3.4. 4. Ground the opposite side of the sphere -some e- will flow to the ground!
5.2.1.3.5. 5. Disconnect the ground wire- this leaves a net + charge on sphere!
5.2.1.3.6. 6. Remove the charged rod, the net charge has to stay on sphere.
5.2.1.4. Explain why a stream of water bends towards a charged rod.
5.2.1.4.1. Negative charges on the stream of water are attracted to positive charges on the rod.
5.2.1.4.2. Forces of attraction between unlike charges is greater than force of repulsion between like charges (because positive charges are closer than the negative charges to the rod).
5.2.2. Induced Charge
5.2.2.1. Definition
5.2.2.1.1. A charge that "appears"on an uncharged object because of a charged object nearby.
5.2.2.1.2. e.g. if a positively charged rod is brought near a small piece of aluminum foil.
5.2.2.2. The Electroscope
5.2.2.2.1. A device that can be used for detecting charge.
5.2.2.2.2. An electroscope consists of a metal knob connected by a metal stem to two thin, lightweight pieces of metal foil, called leaves
5.2.2.2.3. How can the electroscope be used to determine the sign of charge?
5.2.3. Earthing/grounding
5.2.3.1. The process of connecting a body to earth to discharge it is called earthing
5.2.3.1.1. Earthing a negatively charged object means the flow of electrons from the object to earth.
5.2.3.1.2. Earthing a positively charged objects means the flow of electrons from earth to the object
5.2.4. Charging the electroscope by induction
5.2.4.1. Example 1
5.2.4.1.1. If a negatively charged rod is brought close to the knob of the electroscope
5.2.4.1.2. It will cause the free moving electrons in the electroscope to move down into the leaves, leaving the top positive.
5.2.4.1.3. Since the leaves both have negative charge they repel each other and move apart.
5.2.4.2. Example 2
5.2.4.2.1. If a positively charged rod is brought close to the knob of the electroscope.
5.2.4.2.2. The free electrons in the electroscope all start moving up towards the top.
5.2.4.2.3. This means the bottom has a net positive charge. The leaves will spread apart again