gravitational field

negative electric potential

(starting at zero) when a positive charge is brought closer to a negative charge doing work with the field.

positive electric potential

(starting at zero) when a positive charge is brought closer to a positive charge doing work against the field.

Gravitational field lines

- Direction of arrows of field lines show the direction of the gravitational force on a mass placed in the field. -Spacing of field lines indicates strength of field. Closer = stronger.

Conductors

-Contain 'free' electrons which can move between atoms -Eg. Copper has one free electron per atom.

electric field line rules

-Electric field lines point from the positively charged body to the negatively charged body -The lines are drawn uniformly spaced entering or leaving an isolated point charge -The number of lines leaving or entering a charge is proportional to the magnitude of the charge -Field lines do not cross -The line approaches the conducting surface perpendicularly

Test charge

-Point charge used to test magnitude and direction of electric field around an electric charge -Charge: Positive -Mass, charge and size are all negligible - does not alter the electric field in any way

Test mass

-Point mass used to test magnitude and direction of gravitational field around a mass -Mass, charge and size are all negligible - does not alter the gravitational field in any way

potential (rules/things to remember)

-potential is zero at infinite (for both electric and gravitational) -potential is scalar -

gravitational force

-the force is directional proportional to the product of the masses -the bigger the mass the bigger the force of attraction -farther away with masses the smaller the force -- F is proportional to 1/r^2 (r=radius) -the force between two masses

What affects the size of the Earth's pull on you? Why would you weigh a different amount on the Moon?

-the force of the earths pull on you depends on the weight of an object -because the gravitational field strength is smaller the the field strength of the surface on the earth, this is because the mass of the moon is less then the earth

What happens to the strength of the pull of the Earth as you go further away from it?

-the higher you are from the center of the earth, the weaker the field strength (g), and the weaker the force the earth exerts on you.

gravitational potential

-the work done per unit mass on a point mass when it is moved from infinity to that position. -Energy stored by objects due to their position above Earth's surface. -it would take more work, and increase potential energy to moved two planets away form each other -if earth2 has a greater field strength, then when leaving earth you will at first do work against the gravitational field strength, and its at its highest gravitational potential right when you about to go from earths gravitational field to earth2s field. When you pass the maximum point then earth2s gravitational field is doing work, and you are going with the field. -to gain the same potential difference as you go further away from a source, the space between the equipotential lines gets larger in an inverse relationship. This shows how potential energy decrease going away from a source, so more distance to move away from the source is required to have successive changes in potential energy.

What causes the weight that you feel?

-whatever force the earth exerts on you is the same force you exert on the earth ---the earth wont move tho because it is a bigger mass than you are -the gravitational force from the earth because you are in the gravitational field

how does a gold leaf electroscope

-when touched with a positively charged object (polythene rod) , the electrons from the gold leaf electroscope will transfer to the positively charged object, which leaves the leafs positively charged due to the lack of electrons. Because the leafs are positively charged, they will repel one another. -when touched with a negatively charged object (balloon), the electrons from the negatively charged object will transfer to the electroscope, causing the leafs to be negatively charged and repel one another.

Two metal spheres of different size carry charges of −3.0μC and +4.8μC respectively. The two spheres are brought together and the charge distributes itself so that one sphere carries twice as much charge as the second sphere. Determine the charge on each sphere.

1.2 and 0.6

1. How much kinetic energy will an electron gain (in joules and eV) if it accelerates through a potential difference of 23,000 V in a TV picture tube?

23 KeV

Point charge

A point particle with a nonzero charge and no other properties or structure. (it takes up no space)

Point mass

A point particle with a nonzero mass and no other properties or structure. (it takes up no space)

coulombs law assumption

Assumptions: In a vacuum, no external forces

law of conservation of charge

Charge cannot be created or destroyed. It can only move from one place to another or from one object to another.

Insulators

Electrons are generally 'fixed' - they are not free to move between atoms

newtons law of universal gravitation

Every object attracts every other object with a force that is proportional to the product of the two masses and inversely proportional to the square of the distance between their centers.

Electric Field around a point charge OR conducting sphere

The field lines inside a closed and hollow conductor will equate to zero, because the electric field is a vector. Therefore no current in that conductor

Coulombs law

The force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between their centers. The direction of the force is along the line connecting the two charges.

electric field strength

The force per unit charge on a (positive) test charge.

potential gradient

The rate of change of potential with distance moved along a field line

Potential energy, EP

energy an object possesses because of its position in a field.

gravitational field strength equation

g=gravitational field strength F=force that the object will feel when placed at a point m=the mass of the object placed on the field

gravitational field strength equation

g=gravitational field strength G=gravitational constant M=the mass of the planet/object that creates the field R=radius -the bigger the planet, the less the gravitational field strength -the heavier the planet, the stronger the gravitational field strength

how is a balloon charged and why does it stick to the wall

if you rub a balloon against your sweater, the balloon will steal electrons from the sweater, which leaves the sweater positively charged and the balloon negatively charged. The balloon will most likely be attracted back to the sweater because opposite charges attract. The reason that the balloon will stick to the wall is because the negative charges in the balloon will make the electrons in the wall move to the other side of their atoms (like charges repel) and this leaves the surface of the wall positively charged. Because opposite charges attract, the negatively charged ballon will be attracted to the positively charged surface of the wall.

Gravitational field strength

is defined as the force per unit mass acting on a point mass in a gravitational field. -Gravitational field lines can be considered as parallel near Earth's surface. (Uniform field) No significant change in force over small changes in height. Distance from the Earth (r) Value of g R-->1 2R-->1/4 3R-->1/9 4R 5R 6R 7R

As the height of an object in a gravitational field increases,

its gravitational potential energy increases towards zero. It will be zero at infinity.

if field does work

potential decreases (from 0)

if work done against field

potential increases (from zero)

gravitational field

the area around a mass where a force exists if another mass enters the field.

electric field

the area around an electric charge where a force exists if another charge enters the field.

Electronvolt, eV

the energy gained by an electron accelerated through a potential difference of 1 Volt.

what effects the gravitational force on earth

the mass and the radius of the earth

electric potential difference

the work done per unit charge on a positive test charge when it is moved between two points

electric potential

the work done per unit charged on a positive test charge when it is moved from infinity to that position

gravitational potential difference

the work done per unit mass on a point mass when it is moved between two points.

How is a polythene rod charged?

when rubbed with a cloth, the electrons transfer to the cloth leaving the rod positively charged

If the Earth is pulling down on you, then what else must be occurring, by Newton's 3rd Law?

you must be pushing the earth up