Detailed Notes: 7. Fields and Their Consequences: Paper 2: Physics A Level AQA

Force field

A force field is an area in which an object experiences a non-contact force.

Different types of fields are formed depending on which interaction takes place.

1. Gravitational fields

2. Electric fields

Gravitational fields

Formed during the interaction of masses.

Electric fields

Formed during the interaction of charges

Gravity

Acts on any objects which have mass and is always attractive.

Gravitational field strength (g)

Gravitational field strength (g) is the force per unit mass exerted by a gravitational field on an object. This value is constant in a uniform field, but varies in a radial field.

Gravitational potential (V)

Gravitational potential (V) at a point is the work done per unit mass when moving an object from infinity to that point.

Gravitational potential difference

The gravitational potential difference (ΔV ) is the energy needed to move a unit mass between two points and therefore can be used to find the work done when moving an object in a gravitational field.

Equipotential surfaces

Equipotential surfaces are surfaces which are created through joining points of equal potential together, therefore the potential on an equipotential surface is constant everywhere.

Total energy

The total energy of an orbiting satellite is made up of its kinetic and potential energy, and is constant.

Total energy of a satellite = kinetic energy + potential energy

Geostationary satellites

Geostationary satellites follow a specific geosynchronous orbit, meaning their orbital period is 24 hours and they always stay above the same point on the Earth, because they orbit directly above the equator.

Low-orbit satellites

Low-orbit satellites have significantly lower orbits in comparison to geostationary satellites, therefore they travel much faster meaning their orbital periods are much smaller.

Coulomb’s law

Coulomb’s law states that the magnitude of the force between two point charges in a vacuum is directly proportional to the product of their charges, and inversely proportional to the square of the distance between the charges.

Electric field strength (E)

Electric field strength (E) is the force per unit charge experienced by an object in an electric field. This value is constant in a uniform field, but varies in a radial field.

Electric potential difference

Electric potential difference (ΔV) is the energy needed to move a unit charge between two points. Therefore, the work done (ΔW) in moving a charge across a potential difference is equal to the product of potential difference and charge.

ΔW = QΔV

Capacitance (C)

Capacitance (C) is the charge stored (Q) by a capacitor per unit potential difference (V).

C = Q/V

Capacitor

A capacitor is an electrical component which stores charge.

Two types of transformer.

1. Step-up transformer

2. Step-down transformer

Step-up transformer

Increases the input voltage by having more turns on the secondary coil than the primary.

Step-down transformer

Decreases the input voltage by having less turns on the secondary coil.