SP11: Static Electricity Flashcards
SP11a
1) Explain how rubbing an insulator transfers electrons. Explain why this may cause another object to move towards the insulator.
2) Recall the charged particles found in an atom.
3) Explain why, when certain materials are rubbed together, they end up with opposite charges.
1) When insulators are rubbed together, electrons are transferred from one object to another. The insulator that has lost electrons gains a positive static charge, and the insulator that has gained electrons has a negative static charge.
When a positively charged object is held near another object, it slightly repels the positive charges in the object. This induces a negative charge on the surface of the object, so the object is attracted towards the positively charged object, and ‘jumps’ towards it.
2) Two of the subatomic particles in an atom have electrical charges: protons have a positive charge while electrons have a negative charge.
3) Electrons, which are negatively charged, may be ‘rubbed off’ one material and on to the other. The material that gains electrons becomes negatively charged. The material that loses electrons is left with a positive charge.
SP11a
1) Recall the rules of attraction and repulsion between charges.
2) Explain how attraction by induction occurs.
3) Explain why a metal cannot induce a charge
1) The same charges repel each other; while opposite charges attract. Therefore, two negative charges repel one another, while a positive charge attracts a negative charge.
2) If the object is charged, there is a potential difference between two objects. When the potential difference is high enough, electrons jump across the gap to the second object, producing a spark. The object that the spark came from is negatively charged because only negative charges or electrons can move and they will move from an area of negative charge to an earthed area.
3) Metal is a conductor, so when it is rubbed with a cloth, electrons will just flow through it, so no static charge builds up on it and it stays neutral. Therefore, it can’t induce a charge in the paper.
SP11b
1) Describe what earthing is.
2) Explain how earthing works.
3) Explain how lightning occurs and why we sometimes get shocks from everyday objects.
1) Earthing is connecting to the ground directly or indirectly so that electric charge flows from an object, preventing a dangerous build-up of static electricity.
2) Earthing occurs when an object has an unbalanced electric charge. If the object then touches a conductor, such as a metal, electrons will flow between the object and the conductor. Sometimes there is a spark and an electric shock. The electrons will flow in whichever direction removes the excess charge and the object becomes discharged or earthed.
3) Ice and water droplets rub together and cause electrons to be moved between them. This causes a static charge to build up inside the cloud — the top of the cloud has the opposite charge to the bottom of the cloud. This creates a large potential difference which leads to a spark (lightning).
SP11b
1) Explain how electrostatic sprayers work.
2) Describe some hazards caused by charged objects discharging, and how earthing can be used to reduce risks.
1) Electrostatic sprayers work by electrically charging droplets of paint. The charge on each drop is the same as the charge on the other drops, so they repel each other. This means you get a very fine spray. The charge on the object being painted is opposite to the charge of the paint droplets, so it attracts them.
2) A charge can build up when fuel flows through a pipe. Static electricity is dangerous when filling up petrol tanks because if a large static charge builds up, it could cause a spark which could cause a fire or an explosion. One way of reducing this danger is connecting the car to the ground with an earth wire as this allows charge to flow towards or away from the vehicle and stop static electricity building up.
SP11c
1) Recall what an electric field is.
2) Recall how the direction of an electric field is defined.
3) Explain how field lines work
1) An electric field is a region where an electric charge experiences a force.
2) Field lines point away from positive charges and towards negative charges. With a radial field around a positive charge, other positive charges are repelled away. Therefore, the arrows are pointing away from the central positive charge.
3) The lines that represent electric fields are called field lines and they:
- never cross
- show where the field is strongest (which is where the field lines are closest together).
- show the direction of the force on a charge in the field
- start on a positively charged object, for example the point charge, and end on a negative charged object. If there is only one object they keep going, becoming more widely spaced
SP11c
1) Describe the shape and direction of the electric field around a point of charge and between charged electrical plates.
2) Explain how static electricity effects can be explained using the idea of an electric field.
1) In a point of charge, if the charges were free to move, then the charges would move towards each other. As you move away from the point of charge, the strength of the field decreases. The field lines would be around the point of charge, and pointing towards it if it is negative, or pointing away from it if it is positive.
The electric field between two parallel plates is uniform - it is the same in all places between the two points. The electric field lines are straight, with at least three arrows going from the positive plate to the negative plate.
2) The effects of static electricity can be explained using the concept of the electrical field that surrounds all charged particles. When lines of an electric field meet they produce a force. Like all forces this produces movement if the force is large enough to overcome the inertia of the charged particles. This may break the particles apart.
SP11a
1) How can you give an insulator (such as plastic) an overall electric charge?
2) What happens to electrons when the charged object has been earthed?
1) Use friction, and rub the insulator.
2) Connecting to the ground directly or indirectly so that electric charge flows from an object, preventing a dangerous build-up of static electricity. This will remove the excess charge as electrons will move to cancel out the charge, and the negatively charged object has been discharged.
