Fields Flashcards
Newton’s Law of Gravity
Every single particle in the universe is attracted to every other particle by a force that is directly proportional to the product of their masses and inversely proportional to the square distance between their centres
Weight
- The force of attraction acting on an object
- Vector quantity (specific direction)
- (N) unit is a Newton
- Varies depending on position
The gravitational force Earth exerts on any object near or on its surface.
Gravitational force
The force that attracts any two objects with mass
Mass
- The amount of matter in an object
- Scalar quantity (any direction)
- (Kg) unit is kilograms
- Constant throughout the universe
Gravitational field
(definition)
(
- The gravitational force acting per unit mass at a point
- g = F / m (N / Kg)
What are the two types of charge?
Positive (protons) and negative (electrons)
Friction to charge :
Perspex
PVC rods
(silk, wool or fur)
Perspex : Positive - silk
Glass : Positive - wool
Amber : Negative - fur
Rubber : Negative - fur
Polythene : Negative - wool
What is special about neutral objects?
They have an even amount of positive and negative charge
Electroscope
The electrons attracting the gold-leaf will more towards the positive rod and this leaving an excess of protons in the gold-leaf repelling it
How are objects charged by friction?
When two objects are rubbed together there is friction, this causes a certain amount of electrons to be transferred from the one substance to the other - all depending on the substances
How are objects charged by contact?
When two objects come into contact, their charges will combine to create a net charge of both of the objects
How are objects charged by induction?
When two objects are in contact and are neutral, then a charged rod is brought to the one side of the objects - it attracts the opposite charge, also repelling the same charge. This makes the charge different in both of the objects, if separated one will be positive and the other will be negative.
van de Graaf generator
The rubber band creates friction at the collecting comb whilst being moved by a motor, which will cause a gain of electrons - negatively charging the metal dome.
What happens to charge at the points of objects?
The charge will be more concentrated at the points
Spray - painters
Friction on the nozzle negatively charge paint particles. These are then sprayed onto the earthed car body. Since the car is earthed, the paint will attract to the cars surface and repel from each other - spreading out evenly and sticking to the surface.
Photocopying
A drum is charged positively. A piece of paper is scanned and the white areas on the paper will be scanned and let to emit intense light neutralising the same area on the drum. A negatively charged toner is then applied to the drum, which will be attracted to the positively charged area - where the intense light was not emitted. A piece of paper is then run over the drum - the toner is then transferred onto the paper by heating up the toner and fixing it onto the paper
Fly-ash removal
Waste gasses carry ash and dust up a chimney. There are negatively and positively charged rods in the centre with earthed plates on the walls of the chimney. The strong charge creates a strong electric field ionising the air molecules. This then charges the dust and ash which will be attracted to the earthed rods.
Crop spraying
(same as spray - painters)
what is a field?
A way of explaining non-contact forces
What are the similarities between gravitational and electrical fields?
The distance is directionally proportional to the product of their masses or charges and is inversely proportional to the square distance from their centres in order to find the force.
What are the differences between gravitational and electrical fields?
Mass vs charge
Gf is only attraction and Ef is both attraction and repulsion
How are objects charged by earthing?
If a charged rod is brought towards an object, it will draw the opposite charge to it and repel the same charge from it. If this object is now earthed whilst the rod is kept there, the charge that is repelled by the rod will leave the object. If the objet is no longer earthed, the object will remain charged as the charge that was attracted to the rod.
What is an electric field?
A region in which electric charge experiences a force
what is an electric field line?
The path a positive charge would take if it was free to move.
