Physics - Fields

What is the Electric Field Strength?

The force per unit charge acting on a positive test charge in an electric field

What is electric potential?

The work done per unit positive charge in moving a charge from infinity to a point r.

What is Coulomb’s Law?

The force F between 2 charged bodies is directly proportional to the product of their charges and inversely proportional to their separation squared.

If the electrostatic force is positive, how do the 2 charged behave?

They repel

If the electrostatic force is negative, how do the 2 charges behave?

They attract

In what type of field is the electric field strength constant? And what is the formula?

Uniform, E=V/D

In what type of field is the field strength varied? And what is the formula?

Radial, E=Q/4pieR²

What are electric field lines?

The direction a positive test charge will move in

What is the work done to move a charged particle q from A to B between 2 parallel plated of uniform field?

W = q x (change in) V

Explain the motion of a electron travelling at a constant speed through a vertical field.

The horizontal velocity component is unchanged but there is a vertical acceleration upwards from a constant force. Causing the electron to follow a parabolic path towards the positive plate.

How does potential change with increasing distance?

It decreases

How does potential change signs?

If the charge is positive, the potential is positive and the force of charge is repulsive. Vice versa for negative charge.

For a graph of Potential against distance, what does the gradient show?

The electric field strength at any point in that field

How much work is done to move across an equipotential surface?

none

What do the equipotential lines look like in a uniform field?

straight lines parallel to the plates

What do the equipotential lines look line in a radial field?

concentric circles which get further apart with increasing distance

For a graph of electric field strength against distance, what does the area under the graph represent?

the change in potential

How does the charge affect the parabolic shape of a charged particle in motion through a uniform field?

The greater the charge, the greater the deflection

How does the mass affect the parabolic shape of a charged particle in motion through a uniform field?

Increasing mass, decreases the amount of deflection it experiences

How does the speed affect the parabolic shape of a charged particle in motion through a uniform field?

Increasing speed decreases the deflection

What type of quantity is Electric field strength?

Vector

How does electric potential change with increasing distance from a negative charge?

It increases

In the work done equation, what does the q represent?

The charge that is being moved in the potential produced by Q.

How does a cyclotron work?

electron enters a magnetic field in which they experience a force perpendicular to the direction of velocity. This causes the electron to follow a circular path in which the velocity and radius increases for every semicircle (Dee) passed.

How are the electrons acelerated across the gap?

The alternating potential difference switches from positive to negative, the attraction between the negative electron and the positive terminal accelerates the electron towards the opposite plate.

How do the electrons continue to travel in a circular path after crossing the gap in the Dee?

Just before the electron reaches the plate, the pd switches, changing to negative so that the electron repels away at a higher velocity

What happens when the electron reaches a desired velocity in the cyclotron?

It leaves tangentially to the Dees.

What is a gravitaitonal field?

The region of space around an object with mass in which another object with mass will experience a force

What is the gravitational field strength?

The force per unit mass experienced by a 1kg mass at that point

What is the gravitational potential at a point (for a mass)?

The work done per unit mass in moving a test mass from infinity to that point.

Why does a rocket not need to achieve escape velocity to reach their orbit?

it is not leaving the gravitational field so less energy is needed, continuous thrust is provided over the journey so less energy would be needed to overcome gravitational forces further away from the earth.

What is Newton’s Law of Gravitation?

The attractive force between two point masses is proportional to the product of their masses and inversely proportional to their separation squared.

What is Keplers Third Law?

r³/T² is a constant in GM/4pi²

What is a geostationary satellite?

They orbit directly above the equator and have a time period of exactly 24 hours

What is the escape velocity?

The minimum velocity an object must be given to escape a planets gravitational pull when projected vertically from the planets surface.

What is the formula for escape velocity?

(root)2gr