Static Electricity and Magnetism Flashcards
When does an insulator become negatively charged?
When electrons move onto the insulator from a cloth or another object due to friction
When does an insulator become positively charged?
When insulators move off the insulator and onto the cloth due to friction
When do you get an electric shock?
When electrons are stay on your clothes and you touch a metal handle, you get an electric shock because the electrons can conduct to earth (this is an example of earthing)
Why do lightning strikes occur?
- Ice particles in clouds gain electrons from other ice particles due to friction as they rub against each other
- The bottom of the cloud gains electrons and a negative charge
- Electrons in the ground are repelled by the bottom of the cloud
- Lightning jumps to the earth as a spark of electrons
How does electrostatic induction occur when a balloon is near a wall?
The balloon has a negative charge and the wall has a neutral charge, the positive charge of the wall is induced by the balloon, the electrons in the wall are repelled and are moved away, this causes the balloon to be attracted to the wall
What are the main uses of electrostatics?
- Insecticide sprayers
- Paint sprayers
How do insecticide sprayers work?
- The nozzle of the sprayer is connected to an electricity supply
- This causes the droplets of spray all to have the same static charge meaning they repel each other so the spray spreads out evenly
How do paint sprayers work?
- The nozzle of the sprayer is connected to an electricity supply
- This causes the droplets of spray all to have the same static charge meaning they repel each other so the spray spreads out evenly
- The object being painted is given the opposite charge to the paint so the paint is attracted to the object being painted so less paint is wasted
What are the dangers of electrostatics?
- When vehicles move, friction occurs between the body of the vehicle and the air which results in electrons moving onto the vehicle and it becoming charged
- Friction between the fuel and the pipe its flowing through can also cause the transfer of electrons so that the fuel and pipe become charged
- If these charged aren’t removed then when the vehicle comes into contact with another insulator then a spark is caused which could cause an explosion
How can electrostatics be made safe?
- An earthing wire is connected between the vehicle and the ground to ensure the safe movement of electrons off the surface to avoid a dangerous build up of charge
- An earthing wire is connected between the vehicle and the ground
How is the strength of a field shown?
By the amount of field lines
In an electric field what type of charge is it when the arrows are pointing inwards?
Negative, when the arrows are pointing outwards it’s positive
Is electric field strength a scalar or a vector?
A vector because it has size and direction
In an electric field between parallel plates, what direction do the field lines go in?
From positive to negative
In a bar magnet which way do the field lines go?
From north to south, the lines come out of the north pole and flow into the south pole
In a uniform field, how is it shown that the field is constant?
By equally spaced out parallel lines
What is a temporary magnet?
Materials that can be magnetised by bringing a permanent magnet near to it, when the permanent magnet is removed, the temporary magnet loses its magnetism
How can you determine the direction of a magnetic field of a long straight conductor?
Point your thumb in the direction of the conventional current (from + to -) the direction that your fingers curl in is the direction of the magnetic field
What does the size of a magnetic field of a conductor depend on?
The size of the current of the conductor and the distance from the conductor, it is directly proportional to the size of the current and inversely proportional to the distance from the wire
What is the solenoid?
Many coils of wire, the magnetic field lines of each individual coil in the solenoid add together to give a very strong uniform field along the centre of the solenoid, however the field lines cancel to give a weaker field outside the solenoid
What happens if a wire is parallel to a magnetic field?
No force will be experienced
In Fleming’s left hand rule, what do the different fingers mean?
First finger = field
Second finger = current
Thumb = direction of force
How can the size of the force in the motor effect be increased?
By increasing the strength of the magnetic field or the strength of the current
